This podcast is part of a special report on Red Meat. To see the other articles in this series, click here.
I’m sure by now most of you have heard about the news reports about the Harvard study which claimed that red meat increases your risk of death. In this show I present 4 reasons why you shouldn’t take these claims seriously. I also discuss several reasons why eating red meat is beneficial to your health, as well as one little known reason that some people may need to limit red meat consumption (hint: it has nothing to do with saturated fat, cancer or heart disease).
In this episode, we cover:
2:40 Should you worry about the claims against red meat?
7:27 What the research does – and doesn’t tell us about red meat and mortality
38:41 The truth about red meat and colorectol cancer
46:18 Is processed meat bad?
58:08 Why red meat can be good for you
1:02:58 One reason you may need to limit red meat consumption
Links We Discuss:
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Full Text Transcript:
Steve Wright: Hi everyone, and welcome to the Revolution Health Radio Show. I’m Steve Wright from SCDlifestyle.com, and with me is Chris Kresser, health detective and creator of ChrisKresser.com. How are you doing today, Chris?
Chris Kresser: I’m doing pretty well, Steve. How are you?
Steve Wright: I’m doing well, as well. I don’t know if I can say that, but I just did. Yeah, it’s been, like, 85 in Michigan and it’s March, so that’s awesome.
Chris Kresser: Well, we’ve stolen the rain from you apparently. It’s actually sunny today, but it’s been raining cats and dogs here for a while.
Steve Wright: Well, keep it.
Chris Kresser: So, this is gonna be my first stand-up radio show here. I got a standing desk, which I’m really excited about, and so we’re gonna record this whole thing with me standing up for the first time ever.
Steve Wright: Do you normally work standing up for, like, an hour at a time?
Chris Kresser: Yeah, I do. I alternate. I still have a sitting desk and a standing desk, and I alternate between the two. But at my sitting desk I sit on a ball, you know, one of those yoga balls, and then I have a chair, and I have this little disk that you put on top of the chair that keeps you moving, keeps your muscles engaged so that I’m not sitting there on my butt all day. So, I’m rarely actually just sitting in my chair. I have a bunch of different stuff that I do throughout the day.
Well, I spend more time than I want to in front of a computer and on the phone, so I have to do something to keep my body active.
Steve Wright: OK, well, we’re gonna have to post some links for that, and I’m gonna have to buy some new products so I can be just like you.
Chris Kresser: Ha-ha, all right.
Steve Wright: OK, cool, so before we get going here, why don’t you grab a drink of water and do some stretches so you don’t hurt anything.
Chris Kresser: Ha-ha, OK.
Steve Wright: And I’m gonna tell the listeners that if you’re new to the Paleo Diet or you’re just interested in optimizing your health, check out Beyond Paleo. It’s a free 13-part email series on burning fat, boosting energy, and preventing and reversing disease without drugs. To sign up, go to ChrisKresser.com and look for the big red box.
And we’re back, Chris. Are you doing OK still?
Should you worry about the claims against red meat?
Chris Kresser: I’m here, and we’ve got a good show today. We’re gonna just take the red meat study that I’m sure everybody has heard about now that claims that red meat increases your risk of death, and we’re gonna just hopefully destroy it, take it to the curb, beat it down, whatever you want to call it. You know, it created such a stir in the blogosphere, and I got so many emails and comments on my blog and questions about it, and I know there has already been a lot written about it, some really great analyses by Denise Minger and Anthony Colpo. Robb Wolf had an article about it. You know, there has been plenty of stuff written, but I want to kind of pull material from a bunch of different sources and just put it all together in a way that’s hopefully very easy to understand. And part of the purpose of this is to educate people on how to critique a study like this on their own. And granted, you know, most people may not ever acquire the skills to do what Denise Minger is doing and some of the other people in the blogosphere and some of the types of critiques that I do, but you can pick up some of the basics pretty easily so that when you see a news report like this you’ll be able to look at it with a discerning eye and not just accept the interpretation of the clueless science reporters and media that just kinda parrot the party line or whatever the researchers claim that their data showed, which as we’re gonna see is often not what their data showed.
Steve Wright: Before we get started here, you got off on a really graphic start. Should we put in a “not safe for work” sign, or are we gonna be tame enough to —
Chris Kresser: Oh, we’re tame. Yeah. That’s gonna be the worst of it, ha-ha.
Steve Wright: All right, well, before we beat all over some scientists and throw all the red meat myths under the bus, how did PaleoFX go?
Chris Kresser: PaleoFX was a lot of fun. I didn’t get to go to AHS last year because Sylvie was born. I mean, so obviously I didn’t regret that, but I didn’t get to meet everybody that I’ve had so much contact with over the last few years via email or through my blog and on the phone, so I was really excited just to meet people and get a chance to hang out with them in person. Spent quite a bit of time with Robb Wolf and to meet Mark Sisson and Jimmy Moore, and of course, all the other folks that were there. And I really enjoyed my talk, the chance to get up in front of people and do my thing. It’s always fun for me. I didn’t really get a chance to see much of Austin. I basically would get to the conference at about 8 in the morning, and I was there both nights until about 9:30 or 10 at night, and so the only part of Austin I saw was my hotel and looking out the window of the shuttle from my hotel to the convention center, which was at the football stadium at the University of Texas. So, there were some great talks. There were a lot of panels that I participated in and some good time just connecting with people. I got to meet some of my long-distance patients, some of whom came from as far away as North Dakota, Maine, so yeah, it was a great trip.
Steve Wright: Awesome, well sounds like from what I read on the Internet, because I wasn’t there, that most everyone had a really good time.
Chris Kresser: Yeah, the organizers did a great job, especially since it was their first conference. I mean, it’s hard to even fathom how many details need to be pulled together to pull something like that off, and it went without a hitch, at least from my perspective, and it was really well done. They had a professional AV crew there the whole time, so I think they’re gonna be putting out a really high quality DVD or a conference package that people will be able to buy if they weren’t able to make it. Yeah, I think it’s a good start for that event. I think they’re already planning on doing it next year, and I’ll definitely go back if they invite me.
Steve Wright: Awesome. OK, well let’s get back to beating up red meat, or —
Chris Kresser: Or beating up the people who are beating up red meat.
Steve Wright: Yeah, that’s what I meant. So where do we start?
What the research does – and doesn’t tell us about red meat and mortality
Chris Kresser: Yeah, I mean, there are so many ways we can go with this, and I think I want to focus it in on four basic problems with the study and with epidemiology research. But first I want to just briefly talk about what the claims were from that study and also from all the media reports that were done afterward. So, there have been a lot of observational studies in the past that have claimed that red meat increases the risk of cancer, especially colon cancer, but this one went even further. It claimed that red meat makes you die of everything, so it increases the risk of total mortality, which is death from all causes. And they followed over 120,000 women from the Nurses’ Health Study and Health Professionals Follow-up Study over 28 and 22 years, respectively, and the data was published by a research group out of Harvard, which for better or worse — I think worse in this case — gives it some kind of instant credibility. You know, a lot of people when they hear Harvard, they think: Oh, it must be true. If it comes out of Harvard, it must be true. And they found that a single serving of unprocessed red meat is associated with 13% increased risk of death from all causes, while a single serving of processed red meat, like bacon or hot dogs, increased total mortality by 20%. And then they made the claim, though they didn’t even study this at all, so I have no idea how they can possibly make this claim, that replacing red meat with whole grains, nuts, and chicken would extend your lifespan. I mean, they didn’t even look at that in their study, so I’m not sure where that came from, but they said it in their report. And in fact, they suggested that 1 in 10 deaths could have been prevented if people limited their red meat intake to under a half a serving a day. So, let’s first talk about the problems with this study, and then we’ll look at other studies that I think are better designed that have examined red meat and particularly the relationship between red meat and cancer, and then we’ll look a little bit at the benefits of eating red meat and why you might want to eat red meat in spite of what this study says, and then we’ll talk about if there are any circumstances where someone might want to limit their red meat consumption and what those would be. So, jump in anytime, Steve, if you have questions so I’m not just sitting here doing a monologue the whole time.
Steve Wright: Got it. Yeah, I don’t have anything yet other than I can’t believe they actually stated that 1 in 10 deaths could have been prevented.
Chris Kresser: Yeah, it’s pure speculation. OK, so it’s hard to know where to start because there are so many things that are wrong with this study, but for the sake of this show, we’re gonna group it into four categories, and I’ll just briefly mention them now and we’ll talk about them each in a lot more detail. So, number one, and I think a lot of my listeners already know this by now, but we’re gonna talk about it in case you don’t, observational studies or epidemiological studies can never prove causality, and correlation is not causation. It’s one of the first things you learn if you study research methodology, and I’m gonna go into a lot more detail about it, but epidemiological studies can only show association. They can show the presence of two variables occurring together. So, for example, in this study the claim is that people who ate more red meat tended to have a higher risk of death, but it does not prove that red meat consumption caused those people to die more frequently than people who were not eating red meat. So, that’s number one. Number two is that the data collection methods that they used in this study were highly questionable, to say the least. Number three was that they didn’t adequately control for confounding variables, and this is related to number one, that it’s a problem with all epidemiological research because we don’t live in a vacuum, so if somebody is eating red meat but they’re also smoking more, exercising less, have higher rates of diabetes, higher body mass index, etc., then how do we know that it was the red meat that increased their risk of death versus all of those other factors? And you know, many of those things that I mentioned are known to affect total mortality. They’ve been shown to do that in other studies. So, that’s a major problem with this study and with epidemiological research in general. Number four, even if all of those weren’t true in number one through three, the data that these researchers presented don’t paint nearly as dire a picture of the increased risk that comes with eating red meat as they would like you to think they do, and we’ll get into that in more detail.
First let’s talk about correlation versus causation or the main problem with epidemiological research. As I said before, anybody who has taken a research methodology course, even at the undergrad level, this is sort of probably what they teach you on the first day. And observational studies where they take groups of people and then they observe them over a period of time — in this case it was over 20 years in both groups — they can’t prove causality. They can only be used to generate hypotheses that should then be studied with a clinical trial, also referred to as an experiment. We should always look at epidemiological or observational research as the first step, and it can be very useful for that. It’s a good way of generating ideas that we would then pursue further with clinical trials, but it’s never the last step. For that, we need to do an experiment, or a randomized clinical trial is kind of the gold standard now, double-blind placebo-controlled if we’re looking at a drug, and these experiments are designed to test the hypotheses that we come up with from epidemiological data. So, using the red meat study as an example, if observational research suggests that red meat increases the risk of death, to prove that that’s true, you’d have to take two groups, or randomize people into two groups, and then put them on two different diets, one that has a low amount of red meat and one that has a high amount of red meat, but then you’d also have to make sure that everything else they’re doing is identical. So, you’d have to make sure that they are all nonsmokers, for example, they’re getting an equivalent amount of exercise, that they have equal rates of diabetes and other conditions that are known to contribute to mortality, that they’re eating a roughly equal amount of fresh fruits and vegetables. You have to make sure that all of those other factors are consistent, which these are known as confounding factors, otherwise we have no way of knowing whether one of those things that changed might be the cause of the change in mortality versus the red meat itself.
So, just to illustrate why observational studies don’t prove anything, we can use some somewhat ridiculous examples. I posted a graphic on my Facebook page with some of these examples a couple of days after the red meat study was published. So, one is that from 2005 to 2011 the number of Facebook users climbed from zero to 750 million, and during that same period the yield on a 10-year Greek bond climbed from 3.6% to 16.8%. So, does this mean that Facebook is driving the Greek debt crisis? Probably not. I think that’s pretty clear to most people, right? We can think back. Another classic example is when you think back several decades ago when the whole “cholesterol causes heart disease” hypothesis was being formulated, there was a great study out of the UK by Professor John Yudkin, and I think his whole goal was to prove the ridiculousness of using epidemiological data to establish causality. And he did research to try to determine what the strongest predictors of heart disease were, and he found that television ownership and car ownership were, in fact, much more strongly correlated with heart disease than cholesterol levels. So, does this mean that owning a TV there’s some toxin in the TV that kind of emits from the screen and zaps your heart and causes you to have heart disease, or that sitting in a car or driving a car around gives you a greater risk of having a heart attack? No, that’s not what that means. It means that there is probably some other indirect factor, like people who own TVs perhaps are less likely to exercise, and low levels of physical activity, we know, is a risk factor for heart disease. So, that’s just another example of how dangerous it is and how silly it can be actually to use that epidemiological data for causality. Another fun one is in Florida ice cream sales and shark attacks are strongly correlated. So, you know, if these Harvard researchers got a hold of that data, they might publish a news story that says that shark attacks are more likely when ice cream sales are high or that eating more ice cream might cause you to be more likely to get attacked by a shark.
Steve Wright: Yeah, I’m not eating ice cream in Florida. Not at all.
Chris Kresser: Ha-ha!
Steve Wright: But, I mean, so with these epidemiological studies, Chris, like you said, they can teach us some things, but is it true that basically what’s happening here is in all of these or most of these epidemiological studies, especially this one, they’re literally, they just have a giant questionnaire, like, lots of questions about all kinds of things, not just diet, and they follow up with these people at random time intervals, and they get all these data points, you know, they said yes or no or 5 or 2, and then they just look at the numbers, you know, they remove everything else and they just look at the numbers, and they’re just hoping to find a couple links. Is that kinda how this works?
Chris Kresser: Yeah, basically. Or they may go into it with a particular idea or agenda or hypothesis, which is probably the case here. And that’s really dangerous, and that’s an important point to raise. Another issue with epidemiological data is, like, you think of the China Study, which has been thoroughly debunked by now, and Denise Minger did the best job of that. If anyone still believes that the China Study shows that red meat causes cancer and is harmful and that saturated fat is bad for you, you definitely have to go over and read her blog post on that. But T. Colin Campbell who put that together is a vegan and has an agenda, and he set out to prove that. And when you look at data and you have an agenda, it’s very easy to find connections and correlations where they don’t really exist and to ignore the things that don’t support your idea. And that’s a big risk that faces any researcher, and it happens in the Paleo/Primal community too, and it’s something I try to constantly be aware of. I’m human. I have the tendency just like everybody else. I think it’s a natural human tendency to want to find things that support our worldview and our way of looking at things, but I do my best to guard against that, and I think it’s really important to be aware of that because it’s one of the real risks of interpreting this kind of data.
I’m gonna talk a little bit more about the data collection methods in a second, but I just wanna make a couple more points about the danger of using epidemiological research to establish causality. So, a lot of people probably remember the whole hormone replacement or HRT fiasco a while back, and what happened there was that there were about 30 observational studies that suggested that women taking estrogen had a significant decrease in heart disease risk, so almost 50%, like 45% decrease in heart disease risk. So, there was this mad rush of women then to take estrogen in an attempt to lower their risk of heart disease. Unfortunately later clinical trials, which of course are what are needed to prove or disprove a hypothesis, found that hormone replacement therapy not only didn’t decrease the risk of heart disease, but it actually increased the risk of heart disease by 30%. So, these poor women who had listened to the mainstream media reports on these observational studies suggesting that estrogen would decrease their heart disease risk had actually increased it by 30%. So, this is real. I mean, it’s not just, like, an academic point we’re making here. There are real consequences, and I think it’s irresponsible and borderline unethical and almost criminal for a researcher to come out and say that their data proves something when it clearly doesn’t. There’s really no excuse for that at all, and I don’t understand how a Harvard researcher could say — I mean, this is what Frank Hu, the lead researcher, said: Our data “provides clear evidence that regular consumption of red meat, especially processed meat, contributes substantially to premature death.” That’s just false. There’s no way that statement can be supported, and it might seem like it’s relatively benign, like, if someone doesn’t eat red meat, is that going to kill them? Well, we don’t know what they might choose to replace red meat with and how that might affect their health down the line, and the HRT thing is a good example of how that can go really wrong. So, what happened there was that the observational data that suggested that estrogen was protective — And if you look closer at that data, the women who were taking the hormone therapy smoked less and exercised more and had better lifestyle habits than the women that weren’t taking the hormone therapy. So, those things, as it turned out, were probably what decreased the risk of heart disease, not the estrogen alone, as later clinical trials suggested. So, this is serious stuff, and it has real impact on people’s health and their lives, so I think it’s really crucial to get the word out.
Chris Kresser: OK, so let’s now talk about the data collection methods that were used in this study. But before we get into this, let’s do a little experiment of our own. So, everyone listening to this, take out a piece of paper. If you’re driving, you can skip this step; you can just think about it in your mind. But I want you to write down how many servings of red meat you had last Monday, whenever it is you’re listening to this.
Steve Wright: Ooo, that’s a good one.
Chris Kresser: And then write down exactly how much red meat you had. You know, how many grams of red meat did you have at that serving? OK, now I want you to do the same thing and tell me how much red meat you had on March 15, 2009. How many grams did you eat during that day? And then I want you to tell me how much red meat you had in March of 2008.
Steve Wright: Um, Chris, I don’t know where I was in 2008.
Chris Kresser: Ha-ha, so how’s your list looking right now? Do you feel confident that you can recall how much red meat you ate four years ago and how often you ate it and how many servings and what amount?
Steve Wright: Yeah, I don’t think so.
Chris Kresser: Yeah, I don’t think so either. I don’t think anybody could. And yet that’s the method that was used in this study. It’s called a food frequency questionnaire, and they ask you to write down, to estimate your food consumption, but they only were filled out once every four years.
Steve Wright: Really?
Chris Kresser: Yeah. Every four years.
Steve Wright: And you had to answer questions about the previous four years?
Chris Kresser: You had to answer questions about the previous four years, how many servings of red meat you had, how much you ate, how many servings of vegetables, fruits, dairy products, and other foods, and you know, most people hardly can remember what they ate yesterday, much less a year ago, much less four years ago. And what’s more important is that even if people could remember what they ate accurately, that’s not what they report on these food frequency questionnaires. Instead they report what they should have eaten. And this isn’t just my opinion. This has been scientifically documented over and over again. Researchers have compared the food frequency questionnaires with more accurate diet records where they take food and they meticulously weight it and measure it, and in fact, a validation report like this has been done for both the Health Professionals Follow-up Study and the Nurses’ Health Study, and I’m gonna read you a quote from each of these validation studies. So, from the Health Professionals Follow-up Study, which is one of the data sets that the researchers reported on, the researchers said: “Foods underestimated by the food frequency questionnaires compared with the diet records (i.e., the gold standard) included processed meats, eggs, butter, high-fat dairy products, mayonnaise, creamy salad dressing, refined grains, and sweets and desserts, whereas, most of the vegetable and fruit groups, nuts, high-energy and low-energy drinks, and condiments were overestimated by the food frequency questionnaires.” And then the validation report from the Nurses’ Health Study came to a similar conclusion and said: The “mean daily amounts of each food calculated by the questionnaire and by the dietary record were also compared; the observed differences suggested that responses to the questionnaire tended to overrepresent socially desirable foods.” In other words, this is just basic human psychology. Most people want to look good. We’re flooded with messages about how fat and red meat are bad and how veggies and whole grains are good, so when people come to fill out these questionnaires, they tend to overreport so-called “good for you” foods and underreport so-called “bad for you” foods.
And if you have any doubt that people misrepresent their food intake on these questionnaires, all you’d have to do is look at the average reported calorie intake for women. So, in this study, the red meat study, women in the first quintile of red meat intake, meaning the women who ate the lowest amount of red meat, reported that they ate only 1200 calories a day. So, you know, for most people, that’s a starvation diet. If they eat 1200 calories a day for 22 years, they would be dead. You know, they’d waste away to nothing. Women in the highest quintile of red meat consumption, on the other hand, reported 2000 calories a day, which is much more likely. So, that’s an 800-calorie gap between those two groups, and that makes it pretty obvious that the difference in their diet wasn’t just about the amount of red meat that they were eating.
Now, there’s been an argument that — You know, some people argue that food frequency questionnaires are accurate because everybody kind of under- or overreports their intake by the same amount, so it all kinda comes out in the wash. Right? However, that’s not actually true. There’s a big difference in the extent to which people under- or overreport their food intake, and some interesting studies out of Australia have shown that the degree to which people distort their food intake depends on their personality characteristics and other factors like gender, age, medical status, body mass index, occupation, how much education they’ve had, and then their use of dietary supplements. So, one study, for example, found that people who have a diagnosed medical condition like diabetes or coronary heart disease are much more likely to overreport their meat consumption, and this is kind of strange when you think about it at first, but it could have something to do with the fact that people who have lifestyle-related health conditions like diabetes or heart disease are less likely to pay attention to what they eat. So, if you’re following this, if people with diagnosed medical conditions that increase your risk of death have a tendency to overreport their meat consumption, then that would have profound effects on any associations you might find between meat intake and mortality, right? So, that’s how they got the data for this study, and I’m personally not at all confident that it’s reliable, and I’m sure most of you after hearing this aren’t either.
Steve Wright: And if you’re not, keep a food journal for, like, 30 days and then try to recall some of those foods, like, every Monday without looking at it and see how you do.
Chris Kresser: Ha-ha, yeah, I mean, this is the work I do, right? I pay a lot of attention to what I eat, compared to most people, I think, and I know a lot about the constituents of food and calories and grams of carbohydrates and fat and serving sizes and all of that, and I would be extremely hard pressed to tell you, you know, how many servings of red meat I had last week or the week before versus a year or two or three years ago. It’s just — It’s impossible.
Steve Wright: Yeah, I’m with you. I pretty much keep a really close eye on what goes into my body, and I don’t know whether I ate red meat last Monday, but I think I did, so I’m not sure. That was only seven days ago.
Chris Kresser: Yeah. So, the next thing we’re gonna talk about, and this is, of course, the problem with all epidemiological data, and it was a problem in this study as well, is that they didn’t adequately control for confounding factors. And I say “adequately” because they did attempt to control for confounding factors using what’s called a multivariate analysis, but as we’re gonna discuss, that’s very difficult to do with any kind of accuracy. So, with any observational data, there’s an almost infinite number of variables that could potentially affect the outcome, some of which we understand and some of which we might not understand very well. So, one example is stress. There’s an increasing amount of research that connects stress very directly as a causal factor to heart disease, and there’s never any mention of stress in any of these studies. They don’t even bother trying to control for it because it’s extremely difficult to control for because it’s so intangible. But there are other factors that are known risk factors for heart disease, like smoking or lack of physical activity or alcohol intake, things like that. So, the questionnaire in the study asked about red meat consumption, but it doesn’t track other things that could potentially be a risk factor that the researchers maybe don’t think is a risk factor or aren’t weighing as heavily as we might. For example, the questionnaire didn’t ask about refined grain intake. It had a question about whole grain intake but not refined grain intake. So, if somebody is eating a lot of burgers at a fast food restaurant, how do we know that it was the red meat that increased mortality rather than the hamburger bun or the hot dog bun that they ate with the meat or the polyunsaturated fat that it was fried in? We don’t.
And then it’s also worth pointing out, which the researchers actually did in their study, they didn’t mention this so much in their reports of the study, that people eating the most red meat were also the least physically active, the most likely to smoke, the least likely to take a multivitamin, which is kind of a proxy indicator for how much somebody is thinking about health in our culture. They had higher body mass index, higher alcohol intake, and a trend towards less healthy non-red meat food choices, so they were probably eating more packaged and processed junk. Also important to note that they had higher rates of diabetes, which is a disease of poor glycemic control that has really no plausible connection to red meat but does have strong links to excess calorie and refined carbohydrate consumption. So, again, if this group of people that was eating more red meat also had higher rates of diabetes, we might think they’re eating a lot more refined carbs and a lot more calories in general and that that was increasing their risk of death rather than the red meat itself. So, as I said, they did try to control for some of these factors with the multivariate analysis, but it’s extremely difficult to objectively and accurately put a value on all of these lifestyle and diet factors that we know contribute to disease, and then there are others like stress that weren’t even a part of the equation. Running a statistical model after the fact is a really poor substitute for a real clinical trial where participants are randomized into two groups and then given explicit instructions on what to eat and then objective measurements of their food intake and then controlling all of the variables so that there aren’t any confounding factors. And then, of course, this is not to mention the fact, as we discussed, that people have a tendency to underreport other unhealthy choices they are making and overreport the amount they exercise and perform other activities that they think are healthy.
Steve Wright: So, we got a plausibly flawed beginning based on just the type of study it was to the conclusion that was drawn, we have an inaccurate way to collect data regardless of what the conclusion would be just in the study design, and we have an inability to accurately discern any correlation because of known problems with what we’re looking at. What else is wrong with this study?
Chris Kresser: Well, one little interesting tidbit here in terms of confounding factors that wasn’t reported on, which I’m not surprised by but it’s pretty interesting: The people who ate the most red meat had the lowest cholesterol, and in fact, the more red meat people ate, the lower their cholesterol was. It was a linear relationship. So, the headline of this study could have just as easily been “Eating red meat lowers your cholesterol,” or even better, “Lower cholesterol associated with increased total mortality,” but of course, that wasn’t what they reported, but it does illustrate again the ridiculousness of using this epidemiological data, and it also shows how convenient it is for researchers to ignore parts of their data set that don’t support their agenda or their hypothesis. The last thing that we’re gonna talk about is the actual data in the study itself and whether the data, when you look at the raw data, is convincing that eating extra red meat is actually correlated even, not causally related but even correlated strongly with an increased risk of death. And if you look at this more closely, another way to summarize the data would be that 286 people would have to reduce their intake of red meat from two servings a day to about a half serving a day for 22 years to save one life, or that those same 286 people would need to eat about 3.2 million more pieces of meat between them to kill one more person over 22 years. And that’s assuming, of course, that this data was accurately reported, which it wasn’t, and that it controlled adequately for all of the confounding factors, which it didn’t. So, when you look at this way, even if all those other things were not true that we’ve already talked about, it doesn’t exactly sound like cause for alarm, does it?
Steve Wright: No, no, I’m not really concerned anymore.
Chris Kresser: Ha-ha, I don’t think you ever were, Steve, but —
Steve Wright: Yeah, you’re right. I’m eating a steak right now.
The truth about red meat and colorectal cancer
Chris Kresser: Ha-ha, OK, so let’s talk briefly about other studies that have been done on the association between red meat and health problems like cancer. That’s the most common thing is you see these correlations between red meat and particularly colorectal cancer, and to the point where a lot of people just take that as a given. There have been more than 50 epidemiological studies done on that association, and probably, like, in the last 20 years, I think 35 of those were prospective studies. There’s a really great paper that critically analyzes the claims that are made that show an association between red meat and colorectal cancer, and we’ll put that in the show notes. But basically these researchers did a meta-analysis of all of these studies, and they found that the associations were very weak in magnitude; the relative risks were below 50%; most of the studies weren’t statistically significant, which means we can’t be sure that the difference isn’t just due to chance; and there was a lack of a clear dose-response trend, so you didn’t see, like, a linear association where the more red meat they ate, the higher their risk of cancer was. The results also varied by anatomic tumor site, so there’s a stronger association between red meat intake and cancer of the rectum than there is in the proximal colon, and they also varied by gender, so there is no association at all with women and red meat consumption and cancer even though there is a weak association with men. So, the thing is there’s really no plausible explanation for why red meat would be more likely to cause cancer in the distal colon or the rectum than in the proximal colon, nor is there any plausible explanation for why red meat would cause cancer in men but not in women because we have the same basic physiology. And it’s worth noting that the studies on women had a much larger sample size, and there was no association at all in those studies.
And then, of course, there are confounding factors to consider. Red meat has been shown to correlate positively with several known dietary and lifestyle risk factors for cancer. For example, people who consume more red meat also tend to smoke more, consume more calories, exercise less, and eat less fresh fruit and vegetables, and have a higher body mass index. And the researchers in this paper, in contrast to the ones who published the red meat study, were well aware of this, and they said: “Colinearity between red meat intake and other dietary factors (e.g. Western lifestyle, high intake of refined sugars and alcohol, low intake of fruit, vegetables, and fiber) and behavioral factors (e.g. low physical activity, high smoking prevalence, high body mass index) limit the ability to analytically isolate the independent effects of red meat consumption. Because of these factors, the currently available epidemiological evidence is not sufficient to support an independent positive association between red meat consumption and colorectal cancer.” In other words, they said very succinctly what we’ve been talking about in this whole show. There are too many confounding factors to be able to isolate the independent effects of red meat on cancer, and the data of all of those 50 epidemiological and prospective studies that have been done that suggest that there might be an association are not sufficient to prove that. So, some people have argued that, OK, well maybe fresh red meat, unprocessed red meat is OK, but processed red meat is not. And I’ve been wanting to talk about this for some time. I think I did discuss it a while back on another show, but I’d like to cover it briefly again because I think there are a lot of misconceptions out there about processed meat, like bacon.
Steve Wright: Can we do one thing before we get into that?
Chris Kresser: Sure.
Steve Wright: Because I love bacon and I want to talk about bacon. But, say that I’m six months into the Paleo Diet or I’m just starting today, so I’m not, you know, one of us. Tell me, Chris, how you in Chris Kresser’s world who wants to prove or disprove this finally forever that red meat causes or doesn’t cause cancer, tell me how you would set up this study, because I would love to hear you articulate how difficult it would be, because I know how I would do it, and it’s actually not possible in this free society that we live in for this to actually work. So, can you do that real quick?
Chris Kresser: Yeah, well, you’d take a group of people, you’d randomize them into two groups, and then you would put them in a metabolic ward setting —
Steve Wright: So jail basically.
Chris Kresser: Right, basically, like in a hospital. They can’t leave. You would give them the same exact diet, meaning they eat the same amount of fresh fruit and vegetables, they eat the same amount of everything except for red meat, and then you’d give one group a low amount of red meat and the other group a high amount of red meat. Then you make sure they’re all doing the same amount of exercise. You make sure that they’re equivalent in terms of body mass index, they have equivalent rates of diabetes and other modern lifestyle type of diseases. If I were doing it, I would want to control for stress in some way if possible. You make sure that they are not smoking or that they have the same amount of smokers or nonsmokers in each group, and then you would have to follow them for about 25 years, because that’s how long it takes some cancers to develop. The cost of that study would be astronomical. There’s absolutely no way that that could happen, and so, yeah, I agree with you that in this world that we live in, that study’s just not going to happen.
Steve Wright: Yeah, we’re not gonna lock anybody away for 25 years and restrict who visits them and what those visitors have in their pockets and what they eat every day for 25 years. OK, I just wanted to hear that, because sometimes when you’re not too familiar with studies and how they have to be critically designed to control for things, you might not think about what it would actually take to plausibly prove these links, and that’s what it would take.
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Is processed meat bad?
Chris Kresser: Right, but I just want to say that there are other ways you can build a case that wouldn’t be 100% conclusive but that would be more convincing. For example, if we discovered a known carcinogen that’s been studied elsewhere that is in red meat and that red meat had a lot of that carcinogen and nothing else that would offset the effect of it, then that might be a more convincing argument, and that’s why I want to talk about the whole processed meat thing because that’s often an argument used against red meat or at least processed red meat. The idea there is that nitrates and nitrites and nitroso compounds are carcinogenic, as has been seen in some animal studies, but the problem with this is that exposure to these compounds isn’t specific to meat intake, and in fact, exposure to them is a lot higher from other sources. So, here’s another pop quiz: Which of these food sources will give you the most ingested nitrites: 467 hot dogs, one serving of arugula, two servings of butter lettuce, four servings of celery or beets, or your own saliva? What’s the answer, Steve?
Steve Wright: Oh man, you threw in a couple — I thought you were going to make it easy, like, you know, 401, 400, but I’m gonna go ahead and I’m gonna go with the number one, arugula.
Chris Kresser: OK. So, the answer is your saliva.
Steve Wright: Dang it!
Chris Kresser: Ha-ha, but you’re close. Nitrites are produced by your own body in greater amounts than we get from food, in general.
Steve Wright: Is it the same chemically?
Chris Kresser: We’ll get into that in a little more detail here. Salivary nitrites account for 70% to 90% of our total nitrite exposure on a daily basis, but if you consider food alone outside of that, vegetables are actually the primary source of nitrite, and on average, and it varies place to place, but on average we get about 93% of the nitrites we obtain from food from vegetables alone. And yes, nitrite is nitrite, nitrate is nitrate. It’s the same chemical formula, the same chemical composition. So, getting back to the quiz, you were right actually in your guess that a single serving of arugula is the highest dietary source of nitrite. But two servings of butter lettuce and four servings of celery and beets — they’re all equivalent, and they all have more nitrite than the 467 hot dogs. And your saliva has more than all of them. So, the other thing that’s important to understand is that nitrite has beneficial impacts on immune and cardiovascular function. In fact, it’s been studied recently as a potential treatment for hypertension, heart attacks, sickle cell disease, and some circulatory disorders. And besides that, there’s very little nitrite in cured meats, as our pop quiz illustrated. The USDA only allows about 120 parts per million of nitrite in hot dogs and bacon, but during the curing process most of that nitrite forms nitric oxide, which binds to iron and gives hot dogs and bacon that pink color that they have, and the amount of nitrite left after that is only about 10 parts per million. It’s also really important to understand that neither nitrate, nor nitrite really accumulate in the body in significant amounts. When we get nitrate from food, it’s converted into nitrite when it contacts the bacteria in our saliva, and then about 25% of the nitrate we eat is converted into salivary nitrite, and 20% is converted into nitrite in the gut. The rest is excreted in the urine within about 5 hours, and what nitrate is observed has a very short half life. It disappears from our blood stream in about 1 to 5 minutes. Some nitrite in the stomach reacts with the gastric contents and forms nitric oxide, which may have some beneficial effect. That’s been studied a lot lately. And you kind of alluded to this, Steve, but the so-called natural nitrite or nitrate, or nitrite- and nitrate-free hot dogs and bacon, they use naturals sources of the same chemical, like celery and beet juice and sea salt, but it’s still NO3, which is nitrate. And as Mat LaLonde is fond of reminding us, when it’s the same chemical structure, it’s the same chemical. They’re no more free from nitrates and nitrites than the standard hot dogs and bacon. They have the same chemical. It’s just a different source. So, I think the whole nitrite and nitrate things is overblown. The WHO, World Health Organization committee on food additives says that the safe range is about 0.1 mg/kg/day, and in order to exceed that, you’d have to eat about 2222 hot dogs every day.
Steve Wright: Whoa!
Chris Kresser: Good luck with that, ha-ha. Even the hot dog eating contest winners aren’t coming close to that.
Steve Wright: No, I think we might be OK in the hot dog realm. So, the big question is do you eat bacon, then, that has nitrites on the label?
Chris Kresser: Yeah, I mean, I would. We get our bacon from a local farmer, and I don’t think they, I mean, they use natural sources for curing, and you can still buy uncured bacon at the store, but if out somewhere, you know, like on a trip, traveling or something, I’ll eat whatever bacon is in front of me.
Steve Wright: Gotcha. OK. Yeah, and I’m glad you brought up the point about natural, basically it’s preservatives, natural preservatives on a label versus a chemical preservative, and that I think actually what most companies are starting to find is that it’s cheaper and more effective to use the natural than the synthetic forms, and I’m starting to see them all over labels now, the celery extract in the various ones, so I think that’s going to be a growing trend that everyone is going to continue to observe for the next 5 to 10 years.
Chris Kresser: Well, these methods have been used for a long time, right? I mean, curing of meats goes back a very long time, and so they were using these “natural” sources long before the synthetic ones. So, another theory of how red meat might be harmful is it’s not the red meat itself but cooking it at high temperatures, and that creates heterocyclic amines or polycyclic aromatic hydrocarbons, which may be carcinogenic, and I’m certainly open to this as a possibility. There is quite a bit of research that shows that cooking methods do alter the health benefits or effects of food that we eat. Stephan Guyenet has talked about this a few times, and someday I might write an article about it, and I imagine he might, as well, but the study results for the harmful or mutagenic activity of these compounds in relation to colon cancer have been pretty mixed. So, it’s difficult to draw any conclusion about cooking red meat at high temperatures and relationship to colon cancer based on the available data. And then lastly, of course, it’s been suggested that red meat might cause cancer because of its saturated fat content, but there have been good meta-analyses done of the prospective studies in this area that have shown no association at all between saturated fat intake and cancer. And in fact, a lot of recent evidence suggests that conjugated linoleic acid, which is a natural trans fat that’s found in beef, may have anticarcinogenic properties. So, if anything, red meat might be protective against cancer.
Steve Wright: Oh no! Did you just say trans fat in red meat protects against cancer?
Chris Kresser: I sure did!
Steve Wright: Oh man, the FDA’s gonna get us.
Chris Kresser: That’s crazy, huh? These studies are pretty interesting, and it’s one of the benefits of particularly pastured animal products.
Steve Wright: Gotcha. Can we back up one sec on a cooking topic? Did you say anything about advanced glycation end points or AGEs and ALEs? Is that what you were talking about?
Chris Kresser: Not exactly, but that’s another potential mechanism, and you know, I’m curious about this. I’m not sure. I’ve seen some evidence that is pretty convincing, and yet I also think about from an evolutionary perspective the history of how we cooked and consumed meat, you know, directly in a fire for a long period of time before we had slow cookers, and I wonder about that. But in general, I think there are a few reasons that it’s probably a good idea to eat meat, and food in general, that’s prepared with gentle cooking methods and particularly if you have a gut issue. I mean, the slow cooked foods or the braised foods, low temperature cooking methods can make these foods, especially when you’re using broth, a lot more assimilable. So, personally I don’t avoid high temperature meat all the time. We have a grill. I sometimes use it. I don’t really tend to fry things, but I will grill things occasionally. But I do favor stews or low temperature roasting or slow cooking or braising, things like that, because I just feel like it’s more nourishing, they’re easily to assimilate and digest, and I’m also kind of hedging my bets a little bit until I’m more clear on the effect of cooking temperatures.
Steve Wright: And the cooking temperature problem — correct me if I’m wrong — is because the protein structures at different temperatures will actually go from, say, a line to a ball and they’ll sort of get all crumpled up and then it becomes actually hard to break them back apart once it’s in the body?
Chris Kresser: Yeah, I mean, there are a lot of different theories. That’s one, and then we just talked about these heterocyclic and polycyclic compounds that may be carcinogenic, and AGEs, and there are really quite a few ideas about what could be a problem. So, as I said, I do favor the lower temperature cooking methods for a number of reasons, but I’m not afraid of having a grilled ribeye steak every now and then.
Steve Wright: Yeah, it seems like is part of the 0.5% that you need for your health.
Chris Kresser: Yeah, I mean, some people think it might be more significant than that, but I think that if you’re healthy and taking care of yourself in all of the other ways that we talk about, having a grilled steak once a week is unlikely to have a significant impact. That’s just my sense at this point.
Steve Wright: OK.
Why red meat can be good for you
Chris Kresser: Let’s very briefly, because I know we’re getting close to the end of the hour here, talk about some benefits of red meat, and then I want to end up by talking about who, if anyone, should limit their red meat consumption and why. So, red meat, I think, is one of the best meats from the perspective of the omega-6 to omega-3 fatty acid ratio, and that’s particularly true of pastured beef because — The main difference actually between pastured and grain-fed beef is not the omega-6 content, it turns out to be about the same in both, but the omega-3 content, which is about three times higher in pastured beef, and of course, it’s the ratio that we’re concerned with between omega-3’s and omega-6’s. So, pastured beef has three times more omega-3 than corn-fed beef or factory-raised beef, and so it’s gonna have a better ratio. That, in turn, has a beneficial impact on inflammatory loads, less likely to cause inflammation. Red meat is a good source of other fats like saturated fat and then the natural trans fat that we just talked about, conjugated linoleic acid, which may be anticarcinogenic. It’s particularly nutrient dense. It’s a great source of a lot of vitamins and minerals and actually a very absorbable form of these vitamins and minerals. So, for example, beef is a great source of heme iron. Heme iron is much easier to digest and absorb than the ferrous form or plant forms of iron. For example, when I have patients with iron deficiency, I’ll often recommend if they’re not already eating a lot of red meat, eating red meat or liver and oysters, and that can bring up their iron significantly. A lot of people who take iron supplements experience gastrointestinal discomfort, constipation, and things like that, and that’s because usually the form of iron in there is the ferrous form and it’s not well absorbed and it can be hard on the gut. Red meat, of course, is a great source of zinc, as well, and we talked about in a previous show the problems associated with zinc deficiency or excess copper, or elevated copper-to-zinc ratio. And then red meat is a really highly assimilable source of protein, easy for the body to break down. It’s a complete protein. So, there are a lot of reasons to eat red meat, especially pastured red meat.
Steve Wright: So, if you had to, like, if we wanted to rank meats, when maybe we actually don’t even want to, but if we had to rank meats just based on o6 and the ratio of omega-6 to omega-3, what would be the order of the meats that you would eat? If you were basing it just on the o6/o3, which is not the only consideration you should give or take.
Chris Kresser: Yeah, I mean, from the commonly consumed meats?
Steve Wright: Yeah.
Chris Kresser: Beef is number one. Lamb, I think, would be next.
Steve Wright: What about seafood?
Chris Kresser: Well, seafood is higher, I mean, like, salmon has significantly more omega-3 and not very much omega-6, so that would be the highest. Beef would be the number one for the commonly consumed meats, I think lamb would be next, pork would be after that, and then chicken comes up last actually, which most people are surprised by, especially the dark-meat chicken or chicken with skin. So, that’s kinda the hierarchy. If you throw game meats in there, wild game meats, it’s different, and I don’t know those off the top of my head, but in general, they tend to be lower in omega-6 especially because they’re not factory farmed, you know, so they’re all kind of pastured for the most part.
Steve Wright: Right, and then if you wanted to throw one more, like, you wanted to just put eat more red meat on there, I would say that polyunsaturated fats, which we’ve talked about before, oxidize quickly within heat, which is another problem that people talk about when they talk about what temperature are you cooking your meat. So, therefore, if you have a high load of omega-6 plus omega-3 fat in the type of meat, which is true in poultry versus red meat as much lower, you might consider red meat a better meat at that point too.
Chris Kresser: Yeah, fried chicken in corn oil, dark-meat chicken with skin on it, is probably not the best choice.
Steve Wright: No, ha-ha.
Chris Kresser: Sounds good, though, huh?
Steve Wright: Yeah?
Chris Kresser: No, doesn’t sound good.
Steve Wright: No, not really. It makes my stomach turn a little.
One reason you may need to limit red meat consumption
Chris Kresser: Minus the corn oil, ha-ha! OK, so the last point here, and this really short: There is one population of people that might want to limit their red meat consumption a little bit, and these are people with iron overload conditions like hereditary hemochromatosis, where they have a genetic predisposition to storing excess iron. So, I see a lot of these people in my practice, and my talk at the Ancestral Health Symposium this year is gonna be on iron overload and its consequences, so I’m gonna be talking and writing about it more, but there are different ways to manage it. The main way is phlebotomy or withdrawal of blood. Once you have an accumulation of iron, there are only two ways to get rid of it, and one is phlebotomy and the other is chelation. And chelation therapy has a lot of side effects and is pretty risky and is only indicated if somebody is simultaneously anemic and has iron overload, so they can’t withdraw blood because they’re anemic. But the other thing to do is you have to actually make some dietary and lifestyle modifications to do things to decrease iron absorption and decrease your intake of iron. So, in that situation, you might want to favor fish and pork and maybe light-meat chicken, eat less red meat, and take cod liver oil instead of eating organ meats because liver is a really high source of iron, oysters are pretty high in iron. So, those people would do better eating a little bit less red meat, and if they do eat red meat, there are some more advanced stuff they can do to limit the absorption of iron when you eat red meat that I don’t actually want to get into right now. But it’s a fairly common pattern, but it affects maybe 1 in 200 to 1 in 300 people, I would say. So, that’s pretty much it. I couldn’t really think about any other population of people that would have a reason to limit red meat aside from that.
Steve Wright: Well, that’s good to know because the people I talk with a lot, they have the gastrointestinal issues and they’re already at increased risk for cancer, so I’m glad that we were able to talk about, you know, colorectal cancer and all types of cancers in regard to red meat and the fact that everybody is gonna be just fine.
Chris Kresser: Everybody is gonna be just fine. Good words to live by.
Steve Wright: Yeah.
Chris Kresser: All right, so thanks, Steve, and we’ll see you all in a couple weeks.
Steve Wright: OK, sounds good, Chris. Well, Chris and I would like to thank you for listening today, and please keep sending us your questions at ChrisKresser.com using the podcast submission link. If you enjoyed listening to the show, please head over to iTunes and leave us a review.
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Thanks Guys! This answers a lot of questions – and especially interesting is what I learned about research methodology. One thing we didn’t cover though was why would vegans / raw foodies always seem to talk about the slow transit time / peutrification factor of eating meat – implying that its difficult to digest / breakdown compared to their veggie counterparts (mainly hard to digest legumes!).