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Is the Glycemic Index Useful?


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The idea behind the glycemic index is that we should focus on eating low glycemic index foods because they're not going to raise our blood sugar and that will lead to better metabolic health. Find out the problems with this theory and what the research says.

Revolution Health Radio podcast, Chris Kresser

The research is generally not supportive of either glycemic index or glycemic load for weight loss, insulin or glucose control, or anything else. There are a lot of studies about the glycemic index, but I’m going to talk about the largest, the longest running, and the best controlled trials, and then we’re going to talk about a large review that looked at many different studies.

In this episode, we cover:

2:40  What Chris ate today
9:25  Glycemic index and glycemic load
13:05  Problems with the glycemic index
17:18  What the research says

Links we discuss

Steve Wright: Good morning, good afternoon, good evening. You are listening to the Revolution Health Radio Show. I’m your host, Steve Wright, co-author at SCDlifestyle.com. This episode of RHR is brought to you by Chris Kresser’s course, 14Four.me14Four.me is where you can find his 14-day healthy lifestyle reset program. This is a program for you if you’re struggling to integrate things like diet, sleep, movement, and stress. For instance, maybe you still haven’t lost the pounds you’re looking to lose, still having some digestion discomfort, or maybe the skin issues are coming back now that we’re back into the New Year. If this is an issue for you, if you’re struggling to incorporate these, which is a problem for many of us, including Chris and I struggled with these early on in our journeys, I’d encourage you to check out 14Four.me. Chris has figured out how to make this sort of an easy on-ramp, and you can use it as a reset program that doesn’t even take up your whole month, so check it out at 14Four.me.

Now, with me is integrative medical practitioner, healthy skeptic, and New York Times bestseller, Chris Kresser. Chris, how are you doing?

Chris Kresser: I’m great. How are you, Steve?

Steve Wright: I’m doing pretty well. The weather in Boulder has been out of this world, so I’ve been getting outside and trying to get some sun.

Chris Kresser: Fantastic. That always helps.

Steve Wright: Yeah, 70 in February. That doesn’t suck.

Chris Kresser: Sucks if you’re a skier or a snowboarder.

Steve Wright: This is true.

Chris Kresser: Yeah. So did you get any skiing or snowboarding done last week?

Steve Wright: Not last week.

Chris Kresser: Or the week before, whenever that was, in Utah.

Steve Wright: I was up in Powder Mountain there and just did the Masterminding and the conference, but I was up there a month before that skiing. I’m currently rehabbing my other shoulder. I don’t know if the listeners will remember, but I did have labrum surgery on the left side, and I injured my right shoulder and my right knee playing some competitive pickup basketball.

Chris Kresser: Oh, right.

Steve Wright: Once you get your old coaches and your old teammates involved and your brother, things get a little heated, and I had an incident where I ran into a wall after I got fouled.

Chris Kresser: Uh-huh.

Steve Wright: So I’m on the DL for another week or two.

Chris Kresser: All right. Well, heal fast.

What Chris ate today

Steve Wright: Thanks, man. So before we get into today’s question, what have you been eating all day?

Chris Kresser: Let’s see. For breakfast I had eggs and sauerkraut and leftover Stokes sweet potato. They’re the purple-fleshed ones, which we really enjoy around here. And for lunch I had some local, pasture-raised chorizo and a big salad with avocado and red pepper and some leftover mashed white potatoes.

Steve Wright: Nice.

Chris Kresser: And I have some decaf coffee with full-fat cream here.

Steve Wright: All right. Well, I’m rocking my turmeric-yerba mate blend tea over here.

Chris Kresser: Awesome.

Steve Wright: Good deal. Should we get to this week’s question?

Chris Kresser: Yeah.

Steve Wright: Or do you have any updates before we get there?

Chris Kresser: No, let’s do this question. I do have an update in terms of the show, which is that the episodes might be a little less frequent than has been normal, at least since we switched to this new format where we’re doing weekly episodes, for the next maybe six months or so. On the last show, I talked about the clinician training program and gave you all an update on how that’s going, and I’m preparing to do the deep dive now into the content creation and development phase. I’ve finished the detailed outline and the weekly syllabus, and now all I have to do is fill in the blanks, so to speak, but it’s much like writing a book. It requires a lot of focus and sustained energy, and in keeping with my commitment to myself and to my family that I would not add anything without taking anything away, I’m not taking away the podcast, we’re still going to keep doing it, but I might not do it as frequently. It’s really important to me to maintain this work-life balance and have time with Sylvie and Elanne and time to take care of myself and just get out surfing and take walks in the woods and exercise and just have time to kind of contemplate the deep mystery of life, shall we say?!

Steve Wright: Yeah, just have some downtime.

Chris Kresser: Downtime, leisure time, time to just kind of daydream and not do much of anything. I feel like over the last few years I’ve made a lot of progress in that regard, and in the last four to five months I’ve finally arrived at what feels like — You know, the last few years were admittedly really hectic starting when Sylvie was born right around the time where I started my clinic and my online presence started to grow and things just were really crazy. I did a pretty good job, I think, of maintaining balance during that period, but over the last four or five months things have settled down quite a bit and I’ve really just enjoyed the extra time for all of what I just mentioned, and I don’t really want to give that up again. That’s a little update in terms of the show, so we’ll still be here as we always have been, but it might be a little less frequent than normal.

Steve Wright: Well, I commend you because you’re walking your talk and that’s not always seen in the world.

Chris Kresser: Yeah. I feel like it’s definitely my responsibility. If I’m out there telling people that this is healthy and necessary and if I’m not doing it myself because I can’t make the decisions or commitments necessary to do it, then I’m not being a very good teacher. So here we are. It’ll probably be every other week for a while, maybe a little more frequently when we can. It’s kind of been like that over the past several years, so it’s probably not a huge surprise, and it may be like that again in the future as new programs come and go, but we’ll keep it going.

Steve Wright: Right on. Well, before we get into this week’s question, continue to send us your questions at ChrisKresser.com/PodcastQuestion into your phone or mobile device. We’ll be there a little bit less frequently over the next few months, but we’ll still be archiving your questions and pulling the best ones we can up to the top of the list to help you all out.

Chris Kresser: All right. Well, let’s listen to this question from David. It’s a great question, and I’m sure a lot of people are going to be interested in the answer.

Question from David: Hey, Chris. Hey, Steve. I have a really long commute, and I spent most of the last two months on my commute listening to all of Chris’ podcasts, starting from Episode 1, and I really want to say thanks so much for all the generous and great free content that you guys have provided. Here’s my question: I think in all the podcasts that I heard I don’t remember once Chris mentioning the glycemic index, and this is something that a lot of other functional medical practitioners and people who seem reasonably knowledgeable — guys like Mark Hyman, maybe not fully paleo, but maybe the next best thing — talk about it a lot, and I wanted to see why. Is it that these other guys are on the wrong track thinking about it, or is it that you assume we already know about it? Or perhaps it’s not all that important for people otherwise eating a paleo, higher fat diet. Anyway, let us know what you think about the glycemic index.

Chris Kresser: OK. You know, it is interesting that in all the time I’ve been doing this and writing I don’t think I have written a single article specifically about the glycemic index, nor have we done a show that’s been dedicated exclusively to the glycemic index, so this is now officially going to be the first show or piece of content that’s dedicated exclusively to the glycemic index, so thank you, David, for prompting me to do this. We’re going to just talk. I’m going to give people a little intro into what glycemic index and glycemic load are for those who don’t know, and then we’re going to talk about what the sort of prevailing mainstream theory is about glycemic index. Then I’m going to mention what I think some of the problems are with it, and then we’re going to, of course, talk about what the research says about it, and then we’ll wrap it up.

Glycemic Index and Glycemic Load

Glycemic index is the measurement of a food’s carbohydrate content through its effect on post-meal blood sugar levels, and glycemic load is the number that estimates how much the food will raise a person’s blood glucose level after eating it. One unit of glycemic load is supposed to approximate the effect of consuming one gram of glucose, and glycemic load accounts for how much carbohydrate is in the food and how much each gram of carbohydrate in the food raises blood glucose levels. So glycemic load is based on the glycemic index, and it’s defined as the grams of available carbohydrate in a food multiplied by the food’s glycemic index.

If you’re confused right about now, the relationship between glycemic load and glycemic index can be a little confusing. The best way to think about it is that glycemic load is a weighted measure, a glycemic index-weighted measure of carbohydrate content, and it estimates the impact of carbohydrate consumption using the glycemic index while taking into account the amount of carbohydrate that’s consumed. The glycemic load was basically created to address the shortcomings of using glycemic index alone, and the easiest way of explaining that is probably to just give you an example. Watermelon is a food that is very high on the glycemic index, but a typical serving of watermelon contains very little carbohydrate overall, so the glycemic load of watermelon is very low. That is one illustration of the importance of the difference between glycemic index and glycemic load.

The idea is that we should focus on eating low glycemic index foods because they’re not going to raise our blood sugar and that will lead to better metabolic health. You can look online for lists of low glycemic foods. They’re non-starchy vegetables and certain kinds of fruits, like berries, and then, of course, protein and fat. Things that don’t contain a lot of glucose anyway are low on the glycemic index. And then foods that are high on the glycemic index would be highly processed and refined foods, flour, white sugar, etc., rice cakes, and even things like watermelon, like I said, which illustrates one of the shortcomings of glycemic index.

So that’s the basic theory. It’s been around for a long time. I’m sure everybody’s heard of it by now, and it’s just kind of accepted in the mainstream at this point. And when I say ‘mainstream’, I mean both the conventional mainstream diet approach or philosophy and also the mainstream kind of alternative approach to healthy diet.

Steve Wright: So, Chris, just to kind of recap really quick because I think some people might have gotten a little lost there, tell me if I have this right. Glycemic index is a rating of how much the food and the carbohydrate in the food is going to potentially raise our blood sugar levels.

Chris Kresser: After eating it. Yeah.

Steve Wright: After eating it. OK. And then the load is when we actually take into account how much carbohydrate is in the food rather than just analyzing the carbohydrate itself.

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Problems with the Glycemic Index

Chris Kresser: Thank God you’re here, Steve. You can explain it in layperson’s terms. Yeah, that’s a good description. And glycemic load was basically created to address one of the shortcomings of glycemic index, which is it doesn’t take serving size into account. So watermelon might be fairly high on the glycemic index, but the absolute number of carbohydrates in a general serving size of watermelon is pretty low. Or other foods, like carrots and bread, for example, might be similar in glycemic index, but you have to eat way more carrots to get the same absolute number of carbohydrates than you do bread. That’s one of the shortcomings of the glycemic index, and it can lead to avoiding foods unnecessarily because of their position on the glycemic index. I mean, there’s nothing wrong with eating watermelon for most people occasionally just because it’s high on the glycemic index. It doesn’t make sense.

Another problem with it is that glycemic index only reflects the food’s ability to raise glucose when it’s eaten in isolation. When they developed the index, they just tested it by eating that food alone, but in the vast majority of cases, we don’t eat foods in isolation. We eat them in combination with other foods. If you eat watermelon, you’re probably also eating burgers and hotdogs at a barbeque or something like that, foods with protein and fat that will affect — or if you’re having a salad too, a summer barbeque —

Steve Wright: Or potato vodka.

Chris Kresser: Right! Potato salad maybe, fiber, resistant starch, if it’s been cooked and cooled. All of these things will affect the absorption of the glucose from the watermelon, so it’s not really accurate to imagine that people are eating these foods in isolation.

A third shortcoming is that blood sugar responses to carbohydrate vary tremendously. We know this from studies and also clinically working with patients. I’ve measured my blood sugar extensively over periods of time, and even if I eat a very high carbohydrate meal, my blood sugar will only rise very modestly before returning to fasting level, usually about an hour after I eat. I’ve tried hard to spike my blood sugar, but I can’t, and that’s fairly typical for people who are active and have normal insulin sensitivity and glucose tolerance. Now, of course, somebody else who has glucose intolerance and insulin resistance might eat the same serving of carbohydrates that I eat and see a big spike, so obviously there’s a problem with an index that measures the effect of a food on post-meal blood sugar levels because all that could ever be would be an average because not everyone’s going to experience the same effect. That should be fairly obvious.

Steve Wright: Yeah. Also I’m just curious, I don’t know the answer to this, did the people who were sort of the test subjects that created the averages, is the average already skewed?

Chris Kresser: Well, I don’t know for sure, but I imagine they used a number of subjects to create the average, but even then, we’re not averages, right? It’s the problem with scientific research. We’ve talked about this before. It’s all geared toward averages, but in the clinic we treat patients, we treat individuals, and our recommendations need to be customized based on who we’re talking about.

Glycemic load addresses only one of those three shortcomings because it does take serving size into account, and so I think it’s a better measure than glycemic index, but there are still the same problems, which are that we don’t eat foods with glucose in isolation and also everybody has different responses to glucose based on their own individual circumstances.

What the Research Says

So let’s take a look at what the research says. I think a lot of people might be surprised by this. Generally it’s not supportive of either glycemic index or glycemic load for weight loss, insulin or glucose control, or anything else really that I could find. There are a lot of studies about the glycemic index, but I’m going to talk about the largest and the longest running and the best controlled trials, and then we’re going to talk about a large review that looked at many different studies.

The first was an 18-month randomized clinical trial of a low glycemic index diet for weight loss in Brazilian women, and we’ll put the links in the show notes. This trial found no significant differences in weight loss between low glycemic index and high glycemic index groups. That’s a pretty long trial, and it was a randomized controlled trial.

Then we have the second trial, which was six months and 720 participants and published in the American Journal of Clinical Nutrition, and this one was called The effect of changing the amount and type of fat and carbohydrate on insulin sensitivity and cardiovascular risk, so they were looking at not only GI, glycemic index, but they were also looking at fat. They assigned participants to one of the following five diets. The first was a high saturated fat, high glycemic index diet, which I think they thought would perform the worst. You know, it’s kind of, in the conventional view, the worst of both worlds. Number two was high monounsaturated fat and high glycemic index. Number three was high monounsaturated fat and low glycemic index. Number four was low fat, high glycemic, and number five was low fat, low glycemic. Compliance was good, and perhaps very surprisingly there were no differences in insulin sensitivity between these groups at six months. Now, the caveat here is that all of the groups were eating industrial food. In fact, I think the saturated fat they got through margarine.

Steve Wright: Yummy.

Chris Kresser: Yum. So it’s very likely that if one or more of these groups were eating a real-food diet, regardless of the macronutrient ratios, they would have seen a big difference, and of course, there have been studies done like that on a paleo type of diet, and we’re going to come back to this, so just file that away for now.

Then the third longest trial that I found was four months, and that was 34 subjects with impaired glucose tolerance, so these were people who already had pre-existing blood sugar issues, and they were divided into three groups. Number one was high carbohydrate, 60% of calories from carbohydrate, and high glycemic index, so not only was it high in carbs, it was high on the glycemic index. Number two was high carbohydrate, low glycemic index, and number three was a low carb diet, higher fat diet, mostly from monounsaturated fat. Again, perhaps surprisingly, diet number one, the high carb, high glycemic index, lost the most weight of all three of these, followed by diet number two, which was the high carb, low GI. While diet number three, which was the low carb, high monounsaturated fat, gained weight. The differences were small, but they were statistically significant. The insulin response to the test meal improved, though, in both the high carb, high glycemic index diet and the low carb diet, but not in the high carb, low glycemic index diet.

Steve Wright: Whoops.

Chris Kresser: Yeah, so I wouldn’t blame you for being confused at this point, but what we’re seeing is that there’s not a strong signal here that a low glycemic index diet provides any particular benefit for weight loss or insulin sensitivity or glucose tolerance.

Then there was the review that I mentioned in 2010 called The application of the glycemic index and glycemic load in weight loss: A review of the clinical evidence, and they said in conclusion, “While a few studies found significantly greater weight loss on low GI/GL diets, most of the other studies showed a nonsignificant trend that favored glycemic index and glycemic load diets; suggesting that factors other than GI/GL may play a role.” So there was some trend toward favoring the low glycemic index diet, but that that wasn’t statistically significant, so we can’t really rely on it.

Here’s my take on all of this: It’s not really glycemic index and glycemic load that we need to be concerned with. It’s eating real food. And I know, I feel like a broken record, we’re always coming back to this, but it’s what the research points to. Modern diet research and diet philosophies are so obsessed with macronutrient quantity. It’s all about low carb, low fat, how many grams of carbohydrates do you eat, what percentage of calories from carbohydrates, and that can be important for some people, there’s no doubt about that, but for most people, the quality of the macronutrients that they eat is far more important.

There’s a brilliant paper that I recently came across that looked at this, and it was called Comparison with ancestral diets suggests dense acellular carbohydrates promote an inflammatory microbiota and may be the primary dietary cause of leptin resistance and obesity. Basically the hypothesis in this paper was, it’s not the amount of carbs in the modern diet that’s contributing to obesity and diabetes and all other modern diseases. It’s the type of carbohydrates. And they pointed out that tubers and fruits or functional plant parts that our ancestors would’ve eaten stored their carbohydrates inside of fiber-walled, living cells, and these cells are thought to remain intact during cooking, and so the cellular storage of these carbohydrates makes it almost impossible for a real-food tuber or fruit to have a higher density of carbohydrate than about 25% by mass.

In nature, we just don’t see non-fibrous carbohydrate density exceeding 25%, which means that it’s hard to eat super, super carbohydrate-dense foods in nature, for the most part. But what they called ‘acellular carbohydrates’ in this paper, which are carbohydrates of flour and sugar and processed starch products, they don’t have those fibrous cells, and the carbohydrates are non-fibrous and they can be packed into a food in far greater density than they would typically be found in nature. Essentially what this allows for, according to this paper, is when you eat these types of carbohydrates that are super carbohydrate dense and don’t have the carbohydrates stored away in these living cells, it alters the gut microbiota in a way that promotes inflammation and causes insulin and leptin resistance and then causes eventually overweight and obesity.

I was really excited to come across this paper because it really closely matches my own theories about this and the conclusions I’ve come to from looking at all of the research, not just the modern clinical research, but the anthropological research, and it’s the only kind of theory that really makes sense of all of the different pieces that we have. As we’ve talked about a lot before, we know that cultures around the world, some traditional cultures have very high real-food carbohydrate intake, but they have no insulin resistance or diabetes or any of these problems, and if it really is all about the quantity of carbohydrates and not the quality, that wouldn’t make any sense. But if it’s about carbohydrate quality and not quantity, all of the evidence that we have fits into that description, and we can see that the problems really start not when people eat a high carbohydrate diet, but when they start eating processed and refined, industrial carbohydrates, and this is a very interesting theory for why that would be the case. But whether or not you’re as fascinated by the theory as I am, the end result is the same as it always is, which is that quality is more important than quantity in most cases, and you just have to focus on eating real food and real carbohydrates, starchy tubers, fruit, even legumes and dairy if you tolerate them, if you are a person who has relatively normal blood sugar regulation.

Now, if you have insulin resistance, leptin resistance, and blood sugar dysregulation, you may need to pay attention to the quantity of carbohydrates. Now, I say ‘may’ because when we look at the paleo studies that have shown such dramatic improvements in glucose tolerance and insulin sensitivity and liver fat storage and all of these things even in diabetics, they weren’t restricting carbohydrates. They were allowing people to choose at liberty from all the different types of paleo foods, and when you look at the carbohydrate intake, generally they weren’t low carb diets. They were moderate carbohydrate diets, and yet they were still helping people who were diabetic or prediabetic improve their glucose tolerance and insulin sensitivity and all these other things. So I don’t even necessarily buy the argument that someone who has insulin or leptin resistance has to really severely restrict their real-food carbohydrates because when we look at the research, that’s not necessarily true. It’s often not true when the intervention is using real foods rather than processed and refined foods.

Steve Wright: And as you mentioned earlier, everybody has a different insulin response, and that insulin response can change over time, depending on stress levels and sleep levels and movement levels and things like that.

Chris Kresser: That’s a great point. We’re talking here as if diet is the only thing that affects insulin sensitivity, which is, of course, ridiculous. As you just said, Steve, even just a single night of poor sleep can cause insulin resistance the next day, and physical inactivity, sitting too much, all of those things we’ve talked about before.

So I think the takeaway is there’s no need to really worry about glycemic index and glycemic load if you’re focused on a real-food diet. Most people, especially people with normal blood sugar, can eat starchy tubers and fruit — and not only low glycemic fruit, fruit that’s higher on the glycemic index — and things like legumes and dairy if they tolerate them well without much cause for concern from the perspective of carbohydrate content or quality.

Now, in my book, which is now called The Paleo Cure in paperback, I provide starting points for exploration for percentage of calories from carbohydrates for a lot of different people and different needs because sometimes when you’re just getting started it can be helpful to at least have a kind of idea in mind, and also I’ve worked with a lot of patients who have a really distorted idea of how much carbohydrate they’re eating. For example, somebody might come to me and I say, What’s your carbohydrate intake like? And they’ll say, Oh, it’s pretty moderate. And I’ll ask them what they’re eating, and they’ll say, Well, in the morning I have eggs and some bacon and some greens, and then at lunch I have a salad maybe with some salmon or chicken, and then at dinner I have meat or fish and some greens and half a sweet potato. And I’m like, You think that’s a moderate carbohydrate diet? And the person is, like, a guy who weighs 240 pounds and is doing CrossFit three or four times a week. I’m like, That’s probably less than 10% of calories from carbohydrates, and you’re on an extremely low carb diet, not a moderate carbohydrate diet. I think the fear of carbohydrates has been driven so deeply into people that many people do have a distorted view of how much carbohydrate they’re eating. Even a medium sweet potato is only about 35 grams of carbohydrate, so if that’s the only real significant carbohydrate you’re eating in a day, it’s going to be a really low carb diet unless you weigh about 80 pounds or something.

Steve Wright: And that’s if you have perfect digestion and you think you’re going to absorb every single one of those carbohydrates.

Chris Kresser: Mm-hmm.

Steve Wright: But we won’t open that box.

Chris Kresser: Yeah. So there is kind of an objective way of figuring this out, which is to use a device called a glucometer, and I’ve written an article about this. We’ll put it in the show notes. Basically it’s a device and you can use it to test your blood sugar at home. You prick your finger, get a little drop of blood and put it in the machine, and it gives you a readout. If you’re concerned about your post-meal blood sugar response to meals or you’d like to find out what it is and you’d like to find out what your carbohydrate tolerance is to different kinds of foods, then you can eat a food that you want to test out, like a sweet potato or yuca or taro or fruit. So you test your blood sugar right before that meal, and then you test it at one hour, two hours, and three hours after the meal. You want your blood sugar to be generally below 140 one hour after meals, generally below 120 two hours after meals, and generally back down to your fasted reading, like, where you were before you started the meal, at three hours. That’s general. If you go above those numbers once or twice, it’s not necessarily cause for concern. You’re looking for a pattern.

But many people, I bet, who are listening to this might be surprised to find that if you’re limiting yourself to real-food carbohydrates like all the starchy tubers, plantains, yuca, taro, sweet potatoes, yams, and even white potatoes, for a lot of people, and then fruits, no matter where they are on the glycemic index, you probably will find that your blood sugar stays in the normal range after those types of meals. You might find that if you have a donut or some other processed and refined carbohydrate that your numbers shoot up more. I encourage you to do those experiments, not necessarily eat the donut, but in the name of science, if you have to and you’re not gluten intolerant, I guess it would be OK. You might be interested by what you learn. At least, like I’ve said, from the perspective of the research, real-food carbs don’t have a negative impact on blood sugar for most people.

Steve Wright: Well, I know what I’m doing the rest of the day. It’s all for science!

Chris Kresser: Donuts! Steve’s there going, I wonder what two donuts do to my blood sugar… How ’bout three?! Yeah.

Steve Wright: Maybe some orange juice, too.

Chris Kresser: Right! Throw in some OJ, you’ll really get a look at your blood sugar spiking. No, I mean, I’ve tried. I’ve eaten all kinds of — I mean, I just don’t enjoy eating crap, but I’ve had substantial amounts of honey and juice and things like that, and yeah, the blood sugar will spike a little bit at 45 minutes. It won’t ever, for me, exceed 130, 140 maximum, and even that is rare. And then it goes right back down. This points out the whole importance of biochemical individuality, and we have the tools that we need now to figure out what each person’s optimal amount of carbohydrate is, but my guess is for many people listening, if they stick with the real-food carbs, they won’t even have to think about that very much. And my other guess is that, based on my patient population, most people who are listening who have been following a paleo type of diet and who have been influenced by the low carb ideology are eating fewer carbohydrates than they think they are and may feel better eating more real-food carbohydrates. That’s the trend that we see in our practice.

Steve Wright: Awesome. Well, thank you, Chris, for explaining the glycemic index and hopefully, for some listeners, removing sort of any worry about that index really meaning a whole lot.

Chris Kresser: Yeah. Thanks for listening, everyone. Keep the questions coming. I’m not sure when we’re going to go to the less frequent format, but we’ll either talk to you next week or the week after.

Steve Wright: Yeah, thanks for listening, everybody. Again, if you want to submit your question, we’d appreciate it. Go to ChrisKresser.com/PodcastQuestion. And in between episodes, if you’re not yet, make sure you follow Chris on social media, Facebook.com/ChrisKresserLAc and Twitter.com/ChrisKresser. Thanks for listening and we’ll see you on the next show.

Chris Kresser: Thanks, everyone.

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Join the conversation

  1. Hi Chris, the reason that fruit juice is less likely to spike your insulin and glucose levels is because fructose does not really trigger insulin release. However, there is substantial research, particularly in recent times, which conclusively shows that fructose is the main cause of leptin resistance, and hence metabolic syndrome in general. The liver can not cope with much more than 15g of fructose per day. Fructose is also the major driver of non alcoholic fatty liver disease, poly cystic ovarian syndrome, Alzheimers, depression, heart disease, varicose veins, gout and hypertension.

  2. Thank you Chris for all you are doing to help us! I have one question: throughout the podcast and often in other health articles people say to stay away from refined and processed foods including flour. BUT what about wheat and spelt and kamut that I get straight from a farmer and grind myself? Is that healthy or better in regards to the blood sugar levels?

    Thanks again!

    • Mark, great question!

      In addition to Chris’ presented research check out the work of Prof. Willett (Havard, database of 43,000+ cases), Prof. Lustig, Prof. Johnson (fructose!!) and others.

      A great video is this http://youtu.be/xaLbq1H958s where the importance of fermentation of grain and other foods is discussed, e.g. bread was originally only made after soaking and sourdough based (sourdough bacteria eating empty carbs and breaking down gluten).

      If you have direct access to farmer, great!! Try a yeast-free homemade sourdough bread made with sprouted flour (try spelt, rye) and you see it is simply a different food. Still a fair glycemic impact (don’t eat daily, a sandwich made with such bread is around GL 7-9, a single banana is GL14 to 16). A healthy gut can digest these breads with ease. Not for the daily paleo diet, but great for post-workout.
      It is the fructose (in almost every packaged food/juice and in super-sweet-bred fruits) and the processed, fast, yeast-based bread that’s killing us, not the gluten itself. However, the gluten panic is a topic on its own.

      Entire Universities have dedicated their work to the Glycemic Impact in humans, e.g. University of Sidney (they also host http://www.glycemicindex.com).
      BTW great folks, contact them if you want to dig deeper.


  3. Chris you mention 3 very valid shortcomings of Gi but miss 2 other ones I think equally important – low GI often can mean high fructose, because the glucose is reduced in favour of fructose, and this has a terrible effect on the liver and causes weight gain – and the second is that total carb is still relevant in that low GI may not spike your blood sugar as quickly, but you will keep your blood sugars at a higher level for a longer period of time, as your system converts the total amount of carb over a longer period of time.

  4. So we’re standing in the grocery store aisle, contemplating a package of something …

    GI and GL are not in general useful, unless they are the only numbers you have, and both are zero.

    Firstly, GI and GL are almost never found on the product package or in a recipe in the US, except possibly for some products explicitly sold as “dietetic” or “diabetic”, and those are often still junk for other reasons: too high in available carbs (GI/GL non-zero) and/or contaminated with gluten-bearing grains, soy or rice, or loaded with sugars that are arguably not as low GI/GL as claimed, like dextrose or fructose.

    Secondly, GI and GL don’t account for fructose at all. Fructose doesn’t immediately provoke BG, but rather has more sinister near-term effects.

    What is on the {US} product NF panel, and in any recipe worth contemplating, is “total carbs” and “fiber carbs”. Subtract FC from TC for “net carbs”, and you get a pretty useful number. If it’s less than 15 grams per serving (total for all you eat in the interval), it’s not going to budge BG much. “Carb” also covers fructose (and other ‘oses), so we won’t get blindsided by those.

    And yes, some brands game the fiber number, so we need to read the Ingredients too, but we need to do that anyway.

    The gold standard of BG is, of course, BG, which is easily measured with a glucometer, but for that we have to first buy the product or prepare the recipe.

    Frankly, my impression of GI and GL are that they are slightly-off-the-mark metrics founded with benign intent, that have been co-opted by Big Carb and PDAs (Perpetual Diabetes Associations). The outcome of relying on GI and GL is that people remain confused, fat and diabetic.

    If we don’t like Net Carb, then we might need to be actually measuring BG, and choose foods that keep it below 90 mg/dl fasting and less than 10 higher than that postprandial, out several hours (and yes, that BG target is well below what PDAs advise you – they want to stay in business, after all).

  5. As usual, you’ve confirmed something I’ve been wondering about myself due to my own experiments. Since your posts on people eating too low-carb and Stefani Ruper’s insistence that women eat more carbs I’ve increased my fruit and tuber intake and 7 stubborn pounds just fell off my body. This after 3 plus years of paleo and crossfitting 3 days per week. (Used to be 5 days a week). As a holistic nutritionist and weight loss coach the leading edge nutrition information you provide is absolutely invaluable to me. Thank-you ad infinitum.

    • Wow that’s incredible to hear, Ellie. I’m struggling to lose the last 5 lbs, and I’ve been trying to do keto with bulletproof IF for the past couple of weeks, so I’ve really dropped my carbs to less than 20 net carbs a day. I don’t exercise as much as I used to, but I still walk 30 minutes a day and/or do 10-15 minutes of strength/resistance exercises at home a few times a week. I’ve seen just about no difference but wanted to give myself time. It feels odd to eat so few carbs, not even tomatoes.

    • THANK YOU!
      Women ≠ Men.
      Women have different bone structure, different fat distribution, different musculature, different blood chemistry… women even look different from men, obviously. Why do so many (not all) health “experts” tell women to eat and exercise the same way as men?
      Chris is far closer to the mark with his individuality reminder!

  6. Chris,

    I’d love for a follow-up related to glycemic index and cancer/tumor growth, which is the only reason I pay any attention to it.

    (I’m one of those people you did a podcast for about how to *put on* weight, so that’s not the issue.)

  7. Fifteen years ago I did the doughnut test; 3-1/2 hours after eating a doughnut my blood sugar reading was 47. The highest blood sugar level I recorded was 128, 40 minutes after lunch (peanut butter and banana) while fish, salad and vegs with some pasta was 98. (The kit was acquired to test my dad who had undergone surgery and seemed to be having insulin problems).

  8. I think Chris did a great job here of qualifying when glycemic load may be important. I did not at all conclude that glycemic load is NOT important. I’ll explain.

    Chris qualified that when one eats “real-food”, with plant material still substantially encapsulated within cell walls, the assimilation is slowed to such a degree that we can more or less stop worrying about what it might do to our glucose levels.

    Now before I go on, I’ll say that is how I eat. Exclusively natural, organic, unrefined plants and animals, to the best of my abilities and budget. I eat a lot of plant fiber that is not even starch (because it’s leafy greens) and so releases even less soluble, or digestible carbs than some of the foods that Chris dwells on, such as tubers.

    The point I’d like to make available for some people to take away from this though is that a human can very well, right in their own kitchen, change a “real-food” suddenly into something where glycemic load again becomes very important. Chris reflected on this when he mentioned orange juice.

    People who juice are moving themselves into the arena where they might again have to consider glycemic load, especially if they already have problems with spiking glucose. Any kind of juicing or blending of plant material brings up this issue. So people making “green” smoothies with some kale, but adding a few fruits are, by definition no longer eating “real food” by Chris’ (and my) definition. And remember, that is precisely the caveat that allowed Chris to say that glycemic load may not be important.

    So I’m not changing what Chris says at all. I’m merely appealing to a specific audience to be aware that Chris has laid down a parameter which I consider valid, but which many of us “healthy” people may be violating when it comes to our eating habits. And those people might want to reflect on whether they still need to watch their glycemic load. I know if it were I, being offered a drink of someone’s smoothie, since I’m a recovering hypoglycemic, I would take only a small sip to taste the stuff, but not challenge myself with a great “load”.

  9. Chris, you say that if you try adding OJ to a meal that you will see a spike but I read about someone who made a study on adding OJ to a McDonalds. The OJ-group had a smaller rise in blood sugar as well as c-reactive protein than the groups that got soda and even compared to the group that had water.

    A few years before Super Size Me hit theaters in 2004, Dr. Paresh Dandona, a diabetes specialist in Buffalo, New York, set out to measure the body’s response to McDonald’s—specifically breakfast. Over several mornings, he fed nine normal-weight volunteers an egg sandwich with cheese and ham, a sausage muffin sandwich, and two hash brown patties.

    Levels of a C-reactive protein, an indicator of systemic inflammation, shot up “within literally minutes.” “I was shocked,” he recalls, that “a simple McDonald’s meal that seems harmless enough”—the sort of high-fat, high-carbohydrate meal that 1 in 4 Americans eats regularly—would have such a dramatic effect. And it lasted for hours.

    A breakthrough came in 2007 when he discovered that while sugar water, a stand-in for soda, caused inflammation, orange juice—even though it contains plenty of sugar—didn’t.

    This time, along with their two-sandwich, two-hash-brown, 910-calorie breakfast, one-third of his volunteers—10 in total—quaffed a glass of fresh OJ. The non-juice drinkers, half of whom drank sugar water, and the other half plain water, had the expected response—inflammation and elevated blood sugar. But the OJ drinkers had neither elevated blood sugar nor inflammation. The juice seemed to shield their metabolism. “It just switched off the whole damn thing,” Dandona says. Other scientists have since confirmed that OJ has a strong anti-inflammatory effect.


  10. Very enlightening information, Chris. In light of this, I’m wondering where you would come down on white rice? Would it still be okay to consume in moderation if one has no significant health issues? Thanks!

  11. Chris, great topic, although we think there is not enough research available to make such statements. If you do, the mentioned research would put Paleo in a darker lit: weight gain with low carb, high fat diet. A test with 35 people only, unknown activity level, unknown gut flora, unknown pancreas and health status etc. is useless, sorry. However, have a look at the pro athletes (we have gold medal winner within our contributors): carbo loading is history, high glycemic food is banned, EXCEPT right after workouts. Therefore the constant discussion about macro nutrients is not leading to results. The time when you eat carbs is much more important than any Paleo-Vegan discussion. In addition the calorie system we have created is not considering the actual absorption rate in the body. This is huge. We liked your advice to test glucose levels after eating carbs. Our test show that 90% of all individuals have a blood sugar level after eating a baked sweet potato which you can compare to eating white bread. These are the perfect ingredients to the 90% overweight and obesity epidemic. Eating potato will jepardize any weight loss attempt in non-active individuals. in addition all potatos are GMO (and yes there is a certain percentage aloud in organic as well). Potatos were bred since ever and got topped by the latest USDA approval of the Simplot potato. Conclusion: we have plenty of overweight Vegan and Paleo clients coming to us. They still stay Paleo, but they learn that cooking with too much honey, dates, bananas, potatos etc. will not solve their most important problem: losing weight.

  12. Chris, I am one of those low carbers you were talking about — always afraid of going over 5%-10% of carb intake 😛 THANK YOU SO MUCH for addressing the glycemic index. I’m going to have a guilt-free sweet potato tonight! We’re talking WHOLE FOOD FREEDOM!

  13. Thank you! I was on a low carb diet for a few years and found that I could eat things like potatoes and even bananas in moderation and stay in ketosis. After coming off the diet I was having some perceived blood sugar drop issues and found your article on testing this with a glucometer. Very helpful! The one food that spiked me really bad was gluten-free pancakes. This article explains that and confirms what I had thought–potatoes and bananas are not bad for you!

  14. Chris,

    I’ve only started to scratch the surface of insulin resistance and the unique differences that affect each of us.

    Like all things, not too much, not too little, but just the right amount of sugar can make all the difference. How do we know what the right amount is?

    I highly recommend everyone get a genetic test and start tweaking your diet to suit your ancestry and whatever genetic mutations you have. We usually “know” what our bodies need anyways, but there might be some great advice hidden in you genome you are unaware of.

    I tried getting all my carbs from low-glycemic veges for about a year. When I added potatoes, my health remarkably improved. I think it was beneficial because my ancestors ate a lot of carb, because I have Lyme Disease robbing me of my glucose, and because i do HIIT (anaerobic exercise uses glycogen, while endurance uses fat for fuel).

    BUT potatoes have a high glycemic index. Hmm.

    I’ve experimented with with his pro-fuctose anti-glucose methods, as well as your 30 day diet (which became a year long diet) and what works best for me so far is your diet + potatoes.

    Chris, what is your view on Ray Peats work?

  15. Research is always confusing. No wonder so many people get it wrong when it comes to nutrition. The article has opened my eyes in some things I have never thought of about GI. Thanks

  16. The use of monounsaturated fat in the studies. The only liquid oil I eat is macadamia oil, which per 100ml, has 5g polyunsaturated, 14g saturated and 73g monounsaturated fat. If i eat much of it I put on weight (say more than 250ml a week), where as I can eat several times the amount of butter and not put on weight (I eat about 800g a week). That’s not just adding the macadamia oil – if I eat half the amount of butter and 500ml of macadamia oil I’ll put on weight. So I’m wondering if their use of mono fat has skewed the results. In the second trial they should have done a high saturated fat, low glycemic index diet. The third trial should have ideally had groups with mostly saturated fat and mostly poly fat also.
    What margarine is high in saturated fat? Was it some concoction specially made for the first study?

    • Margarine is “artificially saturated” which is what the process of hydrogenation is, forcing non-saturated fats to become saturated.

  17. oh, and I really hope you approve/post my previous “beyond paleo” comment – I sincerely love kresser and appreciate his evolving views and ongoing research – so my previous comment was intended to be a dose of tough love provocation to Progressive Paleo’s thought leader (Kresser) and the community at large. That’s all. 😉

  18. I can’t wait until you lose the limiting paleo moniker and cease defining diet at all in terms of any carb concept, and no longer have to attach 547 caveats on how although low carb is not for everyone, there are some specific applications. Would save all the mental acrobatics. Save all the *situations for sidebars in all the real traditional / evolutionary blueprint books.

    Missed a big opportunity to rebrand the paperback “beyond paleo.” Perfect moneymaking paradigm shift enabling trick — you have the paleo marketing term for the publishers and faddists currently tuning into the already-antiquated paleo 1.0 of carb phobia – AND you get to redefine it and push it along so people get the cool “live in greater harmony with their ancestral heritage and habitat” meme but also appreciate the 10,000 year post agricultural evolutionary explosion and the beauty of Weston price’s real whole food health-conferring observations across peoples of the world — without dietary alarmism. With carbs and ferments and decidedly non caveman eats. Including hermetic junk some times. Rant over. Just eat the best forms of foods compatible for your present context and eliminate/repair/reintroduce what’s relevant to your physiology, not an arbitrary “paleo” list. Rant over.

    • Cool,
      No because the books focus is on the cure (as the title of the book says), and that cure is strict paleo, not beyond paleo.

      • David – Your comment is either a literal one, or a brilliant dry, sarcastic remark on the state of “paleo.” Not sure, but funny, either way.

        I feel “Beyond Paleo” can encompass Kresser’s version and vision of it — a mostly macronutrient agnostic one where the low carb treatments were the sidebar exception, and the emphasis was on the gut, the ferments, the balance, the lifestyle stuff that Kresser is doing a great job about emphasizing.

        Still doesn’t graduate to a truly post-paleo / blue zone / weston price progressive angle that I think/hope Chris wants to move to / is positioning himself closer to, but I do applaud Chris for moving things along. I guess I’m just embarrassed/afraid to forward otherwise good info on Kresser’s site (a good voice of reason to consider when researching any particular health topic), because I don’t want to appear to endorse that generic paleo template that people seem to be gravitating towards. We’ve been there, done that, the Taubesian Carbohydrate-Insulin hypothesis ought to be just as maligned as the Diet-Cholesterol hypothesis. It’s very easy to get sucked into this site and read a lot of old articles that focus on carbs, carbs, carbs, carbs, rigid “cavemen literally did/didn’t do THIS or THIS maxims and proclamations,” especially in the comments.

        • I find myself nodding in agreement with Cool’s analysis and astute observations. While in profound admiration for Mr. Kessler’s vast health and nutrition acumen…learning so much from his writings…appreciating his thorough research and unending intellectual curiosity…I actually agree that there should be a “Beyond Paleo” title envisioned. Simply love Cool’s term of “macronutrient agnostic”…THIS is the future dietary frame of mind we should seek to embrace for coming to peace with real food.

          • Thanks Donna. I’m hoping that Chris is silently nodding his head as he knows that he’s patiently and methodically positioning himself as a “beyond paleo” guy who utilizes a rough “paleo” framework, but….goes beyond! Seems like the best of both worlds from a marketing standpoint as well as an academic and philosophical and practical viewpoint.

            Because the framework of living in greater harmony with a species’ habitat is great — but the splitting hairs of what is or what isn’t “paleo” food or vilifying foods or classes of food or constituents of foods is NOT!

            Food, and the prep and rituals associated with it, ought to be celebratory, and information on it should be about how to fix your system so that you CAN tolerate more, not about recruiting you to a special club of people who wear their food intolerances like badges of honor.

            [Disclaimer: I don’t consume wheat myself, but I hope to one day be healthy enough to enjoy a quality properly prepared/fermented sourdough, to eat like the French – a little bit of everything, while enjoying robust health and the finest cuisine.] I find it funny how excited some people are to vilify wheat rather than promote the big tent idea that everyone should be eating the best form of any particular food over the idea that everyone should eat some precise perfect template of approved foods. So don’t villify wheat in and of itself, point out that society’s standards for it are terrible, that it’s problematic not just due to increased gluten amount, but because of what industry did to it, because of the additives, because of the roundup pesticide, because of the cutting of steps in the fermentation, because we were over-exposed to antibiotics. At some point, you have to step back and say “grandma lived till she was 90 eating a little bit of everything, bread included — I’m not buying that real food in and of itself is out to get me.” [Disclaimer 2: remember, I said I don’t eat wheat myself; I get it. :)]

            So yeah, getting the industrial crap out of food, that should be the single biggest unifying goal. After that, personal elimination diet testing and experimenting and customization for one’s particular health/fitness goals make sense. Constantly writing articles about how there are misconceptions about the amount of carbs allowed on “paleo” when the diet VERY MUCH was defined by being low carb and low fun (don’t eat this, don’t eat this, don’t eat this, don’t eat this, this food is out to get you), is tedious for everyone involved. If real-foodness of a food determines the level of healthfulness, then keep repeating THAT meme, and don’t use that four letter word (c-rb) at all! Treat exceptions as exceptions. Treat exceptions as exceptions.

            With how many times those of us on a path to recovering health switch beliefs / modify our diets, why would we EVER definitively rule out a food or macronutrient? Sign petitions and get involved with activism to prevent the Organic food label from being rendered meaningless, to keep the legal definition strict and devoid of detrimental stuff, fight monsanto, fight GMOs — don’t split hairs over factions of Christianity — unite over an all-welcoming whole/real food god, and you will have less industrialized food freedom whatever your particular regimen at the time. Sorry for the religious analogy, but hopefully some out there appreciate where I’m coming from and what I’m trying to say.

            • Experiencing major “wavelength” synchronicity here. In my mind, you need not apologize for “the religious analogy”…because promises of the one true path to dietary redemption…via conduits of various dietary saviors are rife in today’s culture. What I find disturbing is the uneasy “sinner” tag this can instill in the unquestioning follower or “disciple”…if their personally chosen macronutrient category or specific food does not align with the guru/priest/priestess’ vision of what is pure…clean…saintly…allowed.

              “Food, and the prep and rituals associated with it, ought to be celebratory, and information on it should be about how to fix your system so that you CAN tolerate more, not about recruiting you to a special club of people who wear their food intolerances like badges of honor.”

              THIS…I concur to the tenth power. Food “intolerances” can be created in macronutrient banishment and used as shields. In the depths of an eleven year waged with anorexia nervosa…I found myself grappling with rules…and kept adding them until I had excluded entire groups of macronutrients…Presently into six months of eating real food from all groups…I find I not only feel better…alive for the first time in years…but I have much improved in the compassion department for difference in others…and not just dietary.

              I agree that eating real food…from every macronutrient group… IS what is contributing to my recovery reclaiming a sense of being a part of humanity in general. “One Way Only” diets…as “One Way Only” religions…are isolating, divisive and judgmental.

              After banning bread for years…(and this living in FRANCE!)…re-introducing my long forgotten pain au levain et seigle (sourdough and rye) has brought great gustatory joy…if not digestive bliss. I seem to have lost my capacities to digest certain grains with any dexterity…but hopefully I will not have to eradicate some of the lovely ones…a work in progress.
              I too, hope to blend into my surroundings… “to eat like the French – a little bit of everything, while enjoying robust health and the finest cuisine.”

              This is how it is and always has been here…and how I used to be, and I look forward to feeling that kind of relaxed normalcy again.


              “So yeah, getting the industrial crap out of food, that should be the single biggest unifying goal. After that, personal elimination diet testing and experimenting and customization for one’s particular health/fitness goals make sense”…

              So refreshing to hear the word “unifying” instead of “vilifying”…this would breed dietary compassion at the very least and why not compassion for our fellow man to boot?

              “Cool”…most definitively…and wise as well.

              • Amen, Donna! Lol

                Glad someone appreciates my rants.

                I’m gonna use this as an opportunity to throw out some heatlh topics I’d love for Kresser to put his research spin on:

                -buteyko breathing
                -oxygen therapies (ozone, h202, hyperbaric chamber)
                -cannabis / endogenous endocannabanoid system

                Whadayasay, Chris?

                Team Kresser: pitch it to Chris!

                Thank you for all you all do, Chris and his entire staff!

  19. Great in depth review Chris. No doubt, the advice the average person receives about nutrition is confusing. I can only imagine what it must be like waking up, with no experience eating healthy, and trying to get answers through Google. We have people with major health issues, unrelated to blood sugar, who are laboring the sugar in their milk while they drink coffee with butter in it.

  20. Perfect timing.

    Was just putting the finishing touches on a chapter about blood sugar in an ebook I’m writing (“12 Ageproof Biohacks”), and this info helped me put the gylcemic load/index in context (real vs fake food).

    Learn a lot here… thanks.