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Do Carbs Kill Your Brain?


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carbs brain fog, carbs and the brain
Could the carbs in that banana be contributing to brain fog? iStock.com/IgorDutina

Recently, I’ve been hearing from many patients who have read Dr. Perlmutter’s new book, Grain Brain, and are now concerned about their carb intake. In his book, Dr. Perlmutter suggests that dietary carbohydrates cause high blood sugar, inflammation, and other effects that lead to a “toxic brain,” which can then develop into neurological conditions such as Alzheimer’s, Parkinson’s, depression, and others. Based on this line of causality, he recommends that everyone consume a very low carb diet (<60g per day) in order to prevent neurological disease.

First of all, I’d like to point out that very low carb (VLC) and ketogenic diets can be effective therapeutic tools for treating many neurological disorders. I touched on this briefly a while back in my podcast with Emily Deans, and initial studies on low-carb diets and mental health have shown promise. (1, 2, 3, 4) Because Dr. Perlmutter is a neurologist, it makes sense that he would be a proponent of low-carb diets for his patients based on these therapeutic effects.

Does eating carbs destroy your brain and lead to neurological disease?

However, recommending a low-carb diet as an intervention for sick people is very different from promoting it as a preventative measure for the entire population, which is what Dr. Perlmutter does in Grain Brain. His approach would be somewhat akin to recommending that everyone go on the Autoimmune Protocol to prevent autoimmune disease, which would be unnecessarily restrictive and unhelpful. It’s important to realize that just because a low-carb diet can help treat neurological disorders, doesn’t mean the carbs caused the disorder in the first place. While I don’t argue with the idea that refined and processed carbs like flour and sugar contribute to modern disease, there’s no evidence to suggest that unrefined, whole-food carbohydrates do. In fact, there are three compelling reasons why this is not the case.

#1 – We Evolved Eating Whole-Food Carbohydrates

The first reason it doesn’t make sense that carbohydrates cause neurological disorders is that we’ve been eating carbs for a very long time, and we’re well adapted to digesting and metabolizing them. For instance, fruit has been part of the human diet for longer than we’ve been recognizably human, and while starch hasn’t been part of the human diet for quite as long, it’s clear that we’ve evolved mechanisms to digest and utilize it efficiently.

Compared with most primates, humans have many more copies of the gene AMY1, which is essential for breaking down starches. (5) This gene is unusual in that the number of copies varies greatly between populations, with more copies present in populations that consume more starch. This indicates that starch played a significant role in our evolution, and some scientists have even argued that consumption of starch was partially responsible for the increase in our brain size.

In addition to possessing the ability to break down complex carbohydrates, our bodies require glucose to function properly and maintain homeostasis. The fact that humans can produce glucose from protein is often used as an argument that we don’t need to eat glucose, but rather than viewing this as evidence that that glucose isn’t important, we might view it as evidence that glucose is so metabolically essential that we evolved a mechanism to produce it even when it’s absent from the diet.

#2 – There Are Many Traditional Cultures with High Carb Intake and Low or Nonexistent Rates of Neurological Disease

If carbohydrates cause neurological disorders, one would expect to see high rates of dementia and similar diseases in populations where carbs constitute a significant portion of the diet. But as it turns out, many of the cultures that maintain the lowest rates of neurological and other inflammatory disease rely heavily on carbohydrate-dense dietary staples. For example, the Hadza of north-central Tanzania and the Kuna of Panama obtain a high percentage of their total calories from foods that are high in natural sugars, such as fruit, starchy tubers and honey, yet they are remarkably lean, fit and free of modern disease. (6, 7)

Other examples include the Kitava in the Pacific Islands, Tukisenta in the Papa New Guinea Highlands, and the Okinawans in Japan. The Kitavan diet is 69% carb, with a high reliance on starchy tubers such as yams, and sugary tropical fruits such as banana and papaya. (8) The Okinawan diet is even more carb-heavy at 85% carbohydrate, mostly from sweet potato. (9) Finally, the Tukisenta diet is astonishingly high in carbohydrate at over 90%. (10) All of these cultures are fit and lean with practically non-existent rates of neurological disorders and other modern chronic disease. (11)

#3 – Modern Research Does Not Support the Notion That ‘Safe’ Carbs Are Harmful

The claim that carbohydrates from whole-food sources cause neurological disorders is not supported by anthropological evidence. In addition, modern studies on the health effects of carb-dense foods such as fruit also fail to support Perlmutter’s hypothesis. In fact, studies overall suggest that eating whole, fresh fruit may actually decrease the risk of health issues such as obesity and diabetes, and that limiting fruit intake has no effect on blood sugar, weight loss or waist circumference. (12, 13)

As you may know if you’ve been following my website, there is plenty of modern research demonstrating that diets rich in refined and processed carbohydrates are harmful. However, this is not due to carb content alone, and there’s no evidence that whole-food carbs have the same effect. When an author or expert recommends excluding or severely limiting one of three macronutrients that humans consume, the evidence demonstrating harm should be strong—not only because of the inconvenience of following such a restricted diet, but because extreme diets (ketogenic or VLC diets in this case) are not always harmless. In my practice I’ve seen many patients who’ve worsened on long-term VLC diets, including those with adrenal issues and poor thyroid function. Long-term VLC diets can also lead to imbalances in gut bacteria due to a lack of prebiotic fiber, which can result in digestive issues.

As I’ve always maintained, you need to find out what works for you and tailor your diet to your specific health goals, rather than follow a canned approach. This is exactly what I’ll teach you to do in my book, Your Personal Paleo Code (published in paperback as The Paleo Cure in December 2014), which is coming out at the end of December.

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  1. I read Grain Brain because I was hoping it would be a good book to give my 75 y/o mother for Christmas. Her own mother had Alzheimer’s and she’s beginning to show minor signs of cognitive decline. IMO, her diet relies too heavily on fruit juice, pasta and whole wheat bread, and I’d love to see her switch to whole fruits, starchy veggies and more healthy fats, eliminating gluten entirely. She doesn’t listen much to what I tell her about diet so I’m looking for a source of information that she’ll respect. I thought Dr. Perlmutter did a great job indicting gluten as harmful to brain health. However, because of his frequent recommendation to dramatically reduce carbs, I decided this isn’t the book for my Mom. Maybe “Your Personal Paleo Code” will be the right book to convince her to get off gluten. What d’ya think, Chris?

    • Wow, someone who has Alzheimer’s in the family, high carb consumption and signs of cognitive decline and a compelling, research-based book by a practicing neurologist is not the right book because his recommendation goes contrary to what one would prefer to eat. Honestly, your mother is the one possibly facing imminent Alzheimer’s. Give her the book written by the neurologist and the Personal Paleo Code, and let her decide which is more compelling and how far she is willing to cut carbs, if at all, to reduce her risk of Alzheimer’s.

  2. So glad you wrote this, Chris. I’m often amazed at the popularity of books that take somewhat extreme viewpoints, but then, I suppose this appeals to many perhaps because it seems to simplify matters. Like so many others, I did VLC for a couple of years and then did not feel well so added in rice and sweet potatoes, cyclically, and many things improved, not the least of which was severe dry eye. I average 100-125 carbs a day and it seems to work very well for me. I very much appreciate your well-thought out approach to diet and health and tend to favor it over a dogmatic approach.

  3. There is a Lysosomal Storage Disorder called Fabry’s disease that our geneticists say only occurs in 1 out of 40 to 60 thousand newborns. They are born either with too little or none at all of the enzyme alpha-galactosidase. This leads to lysosome storage of glucose and glcolipids in the lysosome of the vascular endothelial lining ior smooth muscle. Taiwan in 2009 screened over 177,000 consecutive births and found it in 1 out of 1,250 newborns. This is a very big example of why low-carb, low-fat with “Beano” support can save lives. We do not screen for this in the US. Are you aware of this inherited disorder Chris?

  4. Chris,

    I do plan on getting your book in december, but I am just starting to do a Paleo derived nutrition. I have had digestive issues for over a year and after speaking with my Gastroentologist, he is recommending trying Paleo, he did recommend Ron Wolf’s book in particular cutting out grains/gluten. Digestion is slow, bloating, and so on. But all tests show negative thru colonscopy/upper endoscopy/cat scan/ultrasound, but they did remove gallbladder earlier this summer. Do you have any recommendations in how I should approach it or a book you might recommend?

    Keep in mind, I am very active exercise five days a week, worry about if cutting my carbs too much, will get weak and hurt my workouts and weight loss, what is an acceptable number in terms of carbs per day for someone active?

    • Chris,

      I’ll second Michael. A series on care and feeding of a person, post gall bladder surgery, would be wonderful! (in your spare time.)

  5. I have neurological and mood disorders that can get severe, and restricting carbs has helped a lot. I’m doing the Paleo Autoimmune Protocol and am starting to have some days where I’ve felt better than ever and I’m 33. So your take on this seems more reasonable to me because it is individual.

    Sweet potatoes/yams, winter squash, carob, and coconut work for me, but if I eat fruit… even lower glycemic stuff like berries/apples/pears I want to eat the whole bush/tree and I always find myself wanting to go off on a binder after I have the first piece. I don’t have this so much with the sweet potatoes/winter squash/carob/coconut, but I still have to watch how much I eat of those… especially with the carob/coconut.

  6. Chris, do you think this is a smart approach: reduce your carb intake as much as possible whether you are an athlete or a desk-slave, as long as you don’t notice any obvious and negative effects discernible directly from your level of dietary carbohydrate intake….of course, do this while continuing to vary your diet (eschewing the large majority of grains, legumes and all non-raw dairy)?

  7. Hi Chris,

    Thanks for posting this article.

    I’m interested if you can comment on the transition from a VLC diet to a more regular carb intake. As you have pointed out in this article and many times before the VLC can be a great tool for therapeutic purposes.

    For myself I have had great success with a VLC diet in getting my weight under control. How is it that one can transition back to a higher intake? And, in the case of someone using a VLC to combat Alzheimers would they ever get to a point where it would make sense to reintroduce more whole food carbs.

  8. I have read the Grain Brain, and to be honest it did scare me as my father died this year from Lewy Body Disease, and my grandmother and great-aunt both died from Alzheimers. However your article gives me hope, because whilst I have tried very low carb for several months in order to improve my health, (and this has certainly helped stabilise my blood sugars), I didn’t feel that I could maintain this long term because I didn’t have enough energy. I have been reintroducing fruit to my diet quite successfully along with small amounts of starchy vegetables and rice. So thank you for your balanced opinion which reinforces what I’ve been feeling.

    • So sorry to be blunt, but I think this is a really good example of the danger of such a simplistic critique of Dr. Perlmutter’s recommendations. You have severe neurogenerative disease in your family and a problem with blood sugar control, yet you feel OK adding in plenty of starches because Chris says Paleo carbs are good to go? I really hope you will reread Perlmutter’s book, look at the guest post on Robb’s site and get tested to make sure you are insulin sensitive before you add in lots of Paleo carbs because it’s easier than low carb. There are ways to tweak low carb to increase energy for people that need to remain low carb to prevent neurodegeneration. Of course, you could also wait until you are diagnosed with Alzheimer’s before doing anything, which seems to be what Chris is suggesting–your call!

  9. Thank you Chris for writing this post. It is also in line with what Robb Wolf was saying about Grain Brain, and a post on his site a couple weeks back. Basically, just because a VLC diet is (at least temporarily) therapeutic for metabolically broken individuals (whether it’s in the brain or otherwise), is not a sufficient reason to extrapolate that to the generally healthy (paleo/ancestral) population.

    However, having read the book, I am fully on board with how he has debunked, if you will, a number of conventional wisdom theories. Specificall, that saturated fat is bad and cholesterol is bad. I am also glad that not only did he say the above were not bad for us, he actually provides valid arguments that they are, in fact, absolutely required to maintain our bodies homeostasis. Not to mention the added ammunition this book brings to the war on gluten. I also think the way he has presented this information is straight forward enough for the general public who have limited knowledge in this area and care not for the science. I know all of us in this discussion are well aware of the above facts, but a book like this that is getting a solid level of publicity is just one step in the right direction on the sat fat, cholesterol, and gluten front. Hopefully it will simply lead people to begin their own search for nutrition knowledge, and ultimately end up on this site 🙂

    As always Chris, your insights on topics like this never disappoint, keep up the great work.

    • Hey Andy,

      I’m sure Dr. Perlmutter and I agree on far more than we disagree on. Thanks for your feedback and sharing you experience.

    • Andy, I think you might be referring to the post I wrote for Robb Wolf’s site. Here’s the link, in case anyone wants to check it out: http://robbwolf.com/2013/10/16/carbohydrates-missing-forest-trees/

      I have to say, I wrote my graduate thesis on Alzheimer’s as “type 3 diabetes,” so I’m pretty firmly in the camp that supports low-carb diets for neurological health (and a multitude of other conditions), but I understand and agree with the notion that just because it’s therapeutic for severely damaged people doesn’t automatically mean it’s required for everyone else across the board. More detailed thoughts are in the guest post.

      • Hi Amy,

        Yes, this was the post I was speaking about.

        Thanks for your input on this topic also. It was greatly appreciated also.

      • Wow, this guest post on Robb’s site is excellent. Very thoughtful and nuanced view on the limitations of Perlmutter’s recommendations with reference to individual differences in the ability to regulate glucose adequately based on a variety of different factors. Highly recommended for anyone who is worried about the implications of Perlmutter’s recommendations or who wants to know about the different factors that affect carb tolerance.

  10. Thank you for the common sense perspective. I am reading Grain Brain and have read numerous
    paleo and low carb books over the last few months. I got to the point where I was
    afraid to eat a small organic apple! Too many carbs! I am presently not really eating
    low carb, but I do think I need to reduce my carbs a little, especially the gluten free bread.
    I love a couple of servings of fresh fruit every day and enjoy sweet potatoes and occasional
    rice or quinoa dish. I appreciate the balance this article brings.

  11. As some one with generalized dystonia ( a neurological movement disorder, attributed to genetic predisposition and a head trauma) and working on my Master’s in Nutrition, I eagerly awaited and read Dr P’s book. I was disappointed in some ways but glad to have read it in others. For example, there is not a iota of evidence to suggest VLC helps dystonia, yet he suggests it several times in his book. That said, I follow a whole foods, low carb, gluten free and dairy free diet, albeit with no benefit. To me Dr P’s biggest and most important message was avoiding and/or managing high blood sugars. I regretted that his book had such a “pop” nutrition aspect to it but maybe that is needed to sell books these days. I too- as suggested above- think it suffered from “information bias”

  12. I read his book and it was incredibly helpful. I even started following a very low carb but then realized I was restricting too much. I now am eating more fruits, tubers, sweet potatoes. I think you make a good point explaining that this diet is not necessarily good as a preventative measure. I think you audience is different from his intended audience. Most of your audience is aware of the dangers of processed fruits, especially grains and sugars. He is writing for the general population and does a great job explaining how harmful processed foods are. He also does a great job explaining the cholesterol myth and how dangerous it it’s to have low levels of cholesterol. He is also very informative when he speaks about statins and supplementation a and blood work he suggests. Overall his book is fantastic, but each person needs to use his judgment to decide what is best for him. I think the greatest battle here is to have people rethink all their intake of processed foods, especially grains and sugar, and to stop thinking that taking statins will magically undo all the harm of a crappy diet. Thanks for the post!

  13. Of course it is the carbohydrates.The excess sugars glycate the LDLs that carry cholesterol and fats to the brain, blocking the synapses of the neurons.I don’t know what kind of evidence is needed,is right before our eyes.I could revert the argument:how many doing low carbs or in ketosis get Alzheimer’s?

    • Jose, where is this evidence? There are NO proven links from carbs to Alzheimer’s. Also, to say carbs cause neurological disease is ridiculous. We’ve been consuming high carbs for centuries, and other countries still do and yet Alzheimer’s wasn’t an issue until fairly recently, and not for those other countries. Now highly refined and processed carbs? Maybe. Carbs from whole foods? Almost certainly not. Your statement is way too broad. To say a whole group of macronutrients cause a brain disease caused by prion activity is very far from being factual or based on actual proof.

  14. I been following the work of ray peat and my health has never been better! My diet consist largely of dairy, gelatin,rice, potatoes, small amount of meat, coconut sugar, fruits (dates and orange juice make up a large percent) I average well over 300g of carbs a day in the form of mostly sugar but yet my health continues to improve (as noted via blood test results)

    • And here’s where Chris should say: “I’m very glad this approach helps you. But of course that doesn’t mean it will help everyone, or that it’s even required to avoid Alzheimer’s and other neurological conditions.”

      But he didn’t.

  15. If you’ve read the book you would’ve gleaned the following.

    He is not recommending that we keep fruit and other whole carbohydrates out of the diet, in fact he discusses that whole food is better due to the pectin and the fiber that it contains. However, he recommends keeping the intake lower due to the research that’s come out on the brain and dementia. A high fat, lower carb diet will decrease your risk of a neurodegenerative disease by 40% and a high carb diet will increase risk by 3.6x (Mayo clinic study).

    Perhaps there are areas of the world where they eat higher carb diets, but I live in the United States. Also, Alzheimer’s runs in my family. I’ve been adapting his protocol for a couple of weeks and have been feeling great. Also, I’ve had problems with overeating sugar in the past (even whole carbohydrate) and this is improving since adopting his recommendation for lower carb.

    I do think that each individual will need to tailor this protocol to themselves. For instance if you’re an athlete you’re going to need more carbs.

    As far as evolution, here’s a quote: “Evolutionarily, sugar was available to our ancestors as fruit for only a few months a year (at harvest time), or as honey, which was guarded by bees. But in recent years, sugar has been added to nearly all processed foods, limiting consumer choice. Nature made sugar hard to get, man made it easy.” Dr. Robert Lustig et al

    • I didn’t say that he’s recommending avoiding fruit or whole-food carbohydrates. I said he’s suggesting that carbohydrate intake (from all sources) be limited to 60 grams/day. If I have misinterpreted this recommendation, I’d like to know. Otherwise, my argument stands: there’s no evidence suggesting that eating more than 60 grams of carbs a day in the form of fruit and starchy plants like sweet potatoes and plantains contributes to neurological disease.

      • Here is from his website:

        On the Grain Brain diet I recommend no more than 60grams of carbs/day. However, for extreme athletes, 90-100grams is permissible.

          • You have not misinterpreted this recommendation.

            He spends an entire book talking about specific carbs and then gives a recommendation of a number of carbs. He could have said: “don’t eat grains, don’t eat added sugars, don’t eat industrially processed foods. Fructose is bad unless it’s from whole fruit. Veggies are okay. But don’t eat more than 60g grams of them a day. I have Reactive Hypoglycemia and I can eat more than 60g of carbs a day AS LONG AS THEY COME FROM PROPER SOURCES. I can even eat 60g in one sitting AS LONG AS THEY COME FROM PROPER SOURCES.

            He’s kind of sending a mixed message. If carb source is so important then why only 60g? What if I work out a lot. What if I have a really physcial job? My man wouldn’t be able to do his physical job on 60g of carbs a day.

            Here are a couple of excerpts from Grain Brain (I happen to have had my Kindle eCloud open on my PC – on Grain Brain – when I decided to check your site):

            “…While fructose alone may not have an immediate effect, it has more long-term effects when it’s consumed in sufficient quantities from unnatural sources. And the science is well-documented: Consuming fructose is associated with impaired glucose tolerance, insulin resistance, high blood fats, and hypertension. And because it does not trigger the production of insulin and leptin, two key hormones in regulating our metabolism, diets high in fructose lead to obesity and its metabolic repercussions. (I will clarify later what this means for those who enjoy eating lots of fruit. Fortunately, for the most part, you can have your fruit and eat it, too. The quantity of fructose in most whole fruit pales in comparison to the levels of fructose in processed foods.)… “

            “…When we eat whole fruits, which obviously contain fruit sugar, the water and fiber will also ‘dilute’ the blood sugar effect. If you take for instance, a peach and a baked potato of equal weight, the potato will have a much bigger effect on blood sugar than the watery fibrous peach. That’s not to say the peach, or any other fruit for that matter, won’t cause problems. (4)
            Our caveman ancestors did in fact eat fruit, but not every day of the year. We haven’t yet evolved to be able to handle the copious amounts of fructose we consume today – especially when we get our fructose from manufactured sources. Natural fruit has relatively little sugar, when compared to, say, a can of regular soda, which has a massive amount…”

        • The question above was in response to Chris’ assertion: “there’s no evidence suggesting that eating more than 60 grams of carbs a day in the form of fruit and starchy plants like sweet potatoes and plantains contributes to neurological disease.”

          Dr. Perlmutter makes a very clear argument, that appears to be well supported by research, that in a person with any degree of insulin resistance, upwards of 60 grams of carbs from starchy plants could indeed be contributing to neurological degeneration long before any “disease” was diagnosed.

          Chris, rather than nuancing your critique, you seem to be just hard-headedly stating “No evidence that Paleo carbs can contribute to neurological issues” with no further discussion. I don’t think that’s very responsible of you.

  16. I’m so confused. I’ve soaked my already fogged out brain (low thyroid, taking levothyroxine) over this past week in a plethora of diet/disease info available on the net.

    I think, but not sure just yet, that Chris’s views on this site make the best sense. I just made out my shopping list based on Dr. Cordain’s (sp?) version of Paleo. Now it seems I need to start over again!!! Help! I’ve missed the past 4 weeks of work so please suggest low budget advice to help me get started. Time’s a-wasting!


    • Ginny,

      I’d buy Chris’s book when it comes out, and follow his suggestions. Meantime, for low budget, how about eating a small amount of rice or yams/sweet potatoes with every meal? Say a stingy handful. Eat all the red, orange, yellow and green veggies you want. Eat a couple of fruits per day, preferably one of which is berries. Eat about 3-4 ounces of meat per meal. Learn how to make a bone broth and have a soup made from that plus some veggies daily. Avoid grains, beans and sugar and trans fats.

      Good luck!

      • Thank you Peg! I wish Chris’s book was already out. I’m having symptoms that I suspect might be ALS and I’m terrified. But that can be a good thing since I was such a resolute sugar/carboholic before. Now I am willing to do whatever it takes to minimize/slow or halt the progression of these symptoms, whatever they are. I see the neurologist on Tuesday.

        • Hi Ginny,

          In addition to seeing the neurologist, you should follow the recommendations you find here. So far my personal experience with neurologists (the best in the field) hasn’t been very promising. You may be on your own anyway. You may find yourself tested, diagnosed and then having your symptoms “managed” without any attempt at finding the root cause. You might also try a good functional medicine doc to complement the neurologist. My understanding is that they really are focused on the whole picture and making people better rather than just managed. Good luck to you!

        • Ginny, in my opinion, if you have symptoms that seem anything like ALS you should (beside visiting your doctor, obviously) try the Perfect Health Diet, and in the meantime, buy Dr. Perlmutter’s book and read it.

          He is an MD with specialties in both Neurology and Nutrition, and talks specifically about neurodegenerative diseases, including ALS, which he deals with on a daily basis. He also talks about the tests that you can do to make sure that poor blood sugar control is not contributing to your problems.

          Also, you mention that you were a carboholic. I have this tendency, and I had no success with the Perfect Health Diet simply because it could not keep my carbs to a moderate level. I’ve tried many times to eat “moderate” carbs as the Jaminets recommend, but I eventually end up bingeing on high carb foods. So I’ve finally recognized that for me it’s either very low carb (ketogenic) or high carb. Since I have signs of insulin resistance (abdominal fat) and signs of neurological decline, the very low carb diet is clearly the best choice for me (I never crave carbs when I am doing very low carb).

          Certainly give the PHD a try and if you can keep carbs moderate and you are convinced that you are sufficiently insulin sensitive to handle the carbs (and after reading the book Grain Brain you agree with Chris that there is no evidence that Paleo carbs contribute to neurodegeneration), then great!

  17. Thanks for a great and important article Chris. There has been so much buzz around Grain Brain. In my opinion the book suffers from information bias. Therefore I´m very grateful for your rational approach on the issue. I know both you and I have nothing against Paleo or carbohydrate restriction in general. However, there is no doubt that “Grain Brain” deserves a rebuttal and yours is fair and based on scientific knowledge. Here is mine: http://www.docsopinion.com/2013/11/05/grain-brain-take-grain-salt/