Book Review. Grain Brain – by David Perlmutter

Book Review. Grain Brain The Surprising Truth about Wheat Carbs and Sugar - Your Brains Silent Killers - by David Perlmutter The Health Sciences Academy

by Alejandra "Alex" Ruani — Get free science updates here.

We thought it’d be fun to review a book (in this case Grain Brain) and highlight the kinds of things we noticed that perhaps most readers are not aware of.

Before we get started, just bear in mind that this is not a full, exhaustive, comprehensive analysis. Instead, we’d like to share some pointers so when you do read a diet or health book you keep them in mind.

Grain Brain by David Perlmutter

UK Version | US Version | CA Version

The Book: Grain Brain: The Surprising Truth about Wheat, Carbs, and Sugar – Your Brain’s Silent Killers

The Author: David Perlmutter, MD, is a practicing neurologist and Fellow of the American College of Nutrition. He is also somewhat of a medical celebrity in the US, with a regular slot on the The Dr. Oz Show, and appearing on 20/20, Today, Good Morning America, and The Early Show.

The low-down:

Most of us have heard the message that refined carbohydrates can be bad for our health, but what about other carbohydrates, such as wholegrains and fruit? Virtually all carbohydrates, even those high in fibre, like wholegrains and fruit, are a “health hazard” and are “silently destroying your brain”, says Perlmutter.

The premise of this book is that carbohydrates, defined by him as long chains of sugar molecules, trigger inflammatory responses in the body, leading to disease and brain shrinkage through spikes in blood sugar. Perlmutter goes as far as to suggest that all grains, even wholegrains, are “a terrorist group that bullies our most precious organ, the brain.”

Interestingly, Grain Brain only contains 18 pages of references (many of which are blogs, magazines, and non-scientific sources), compared to 20 pages of index terms and a 43-page plan with a list of supplements to buy and recommended recipes for a carbohydrate-free life. This may provide readers with practical steps for a carbohydrate-free life, but little scientific evidence to support why they should choose such a restrictive diet.

The top 3 highlights

1. It is well written and engaging and, dare I say, convincing. Perlmutter speaks with such passion and conviction about the effects of grains on the brain that his argument is difficult to ignore, particularly with statements such as “when I watch people devour gluten-laden carbohydrates, it’s like watching them pour themselves a cocktail of gasoline,” and his strong belief that “gluten is our generation’s tobacco.”

2. He focuses on health outcomes throughout the book, and not weight loss, which is a positive deviation from typical diet messages. Whilst his views on carbohydrates may be extreme, he is encouraging people to review their diets and is promoting a low sugar diet void of processed foods and high in vegetables, good quality protein, healthy fats, along with a glass of red wine a day (a diet not too dissimilar from the Mediterranean diet, apart from the absence of grains). That said, Perlmutter does not mention the neurotoxic effects of acetaldehydes (ethanol’s metabolites, from drinking red wine). This is a surprising omission (and, dare I say, recommendation) given that most of the book centres on “protecting” the brain!

3. As we know, the brain can function on a low-carbohydrate diet, and Perlmutter indicates that cholesterol is “an essential fuel” for brain cells. “You’ll soon understand why cholesterol is one of the most important players in maintaining brain health and function. Study after study shows that high cholesterol reduces your risk for brain disease and increases longevity,” he states. However, asking whether the brain can merely “function” without carbs is different from asking if the brain can “perform better” without carbs – see here.

Our review

Grain Brain hit number one on the New York Times best seller list, so there is no denying the public interest in this topic, but is the reader getting the whole picture? We reviewed this controversial book to find out.

The foundation of this book is that “eating carbohydrates stimulates insulin production, which leads to fat production, fat retention, and a reduced ability to burn fat”. This generalisation runs across the entire book, where there is no proper distinction made between low-glycaemic carbohydrates vs high-glycaemic carbohydrates, both of which have very different effects on blood sugar and insulin regulation. Instead, Perlmutter suggests that a low-carb diet is the only way to manage your blood sugar and insulin levels. But, as we know, a high-carbohydrate, low-glycaemic diet can too (although this clarification is absent in Grain Brain). For example, spinach is a high-carbohydrate food, but has zero glycaemic value. In other words, eating spinach on its own (a high-carb food) will not raise your blood sugar.

He goes on explaining that carbohydrates increase blood sugar when consumed, which in turn increases insulin release, and that high insulin can eventually lead to insulin resistance. Insulin resistance (a precursor of type 2 diabetes) affects the cells’ ability to absorb glucose, therefore glucose remains in the blood causing inflammation. Perlmutter links insulin resistance and inflammation to the formation of plaques that are present in diseased brains, particularly in Alzheimer’s disease. He describes this link between high levels of insulin and brain disease “type 3 diabetes”.

Although the argument may sound logical, what Perlmutter fails to acknowledge is the evidence suggesting that certain starchy carbohydrates can regulate the insulin response stabilising blood sugar. For example, barley (which is a high-carb, low-glycaemic grain) was recently found to stabilise blood glucose levels. In addition, other research indicates that wholegrains could be beneficial in maintaining a healthy weight, as being overweight is a risk factor for type 2 diabetes.

The Paleo angle

A lot of the argument throughout Grain Brain is based on the observation of our Paleolithic ancestors’ diets, and that anthropological evidence suggests they did not suffer from neurological disease. However, it is worth highlighting that our hunter-gatherer ancestors had a much lower life expectancy.

The Alzheimer’s Society lists “age” as the greatest risk factor in Alzheimer’s disease, and refers to individuals diagnosed with dementia under 65 years of age as “early onset”. It seems unlikely that our primitive ancestors lived long enough to succumb to neurodegenerative diseases. Whilst there is acknowledgement in the book that our hunter-gatherer ancestors did not live as long as those born today into western cultures, there is little connection between shorter lives and degenerative diseases.

Gluten rehab

Perlmutter is a strong believer that most people are intolerant to gluten, but are not aware of it. This doesn’t match with the scientific research, which shows that only up to 13% of the population have non-coeliac gluten sensitivity (more here). When explaining his theory, he states that this gluten sensitivity causes inflammation and that it manifests itself not only in the gut, but in the brain. This could be as a simple headache or migraine, or more sinister neurodegenerative diseases. As a result, his book strongly recommends everyone stops eating gluten immediately, regardless of apparent symptoms. But is this the best advice?

Studies have reported changes, potentially adverse, in gut microbiota in response to a gluten-free diet due to the reduction in intake of naturally-occurring fructans (found in wheat), which have prebiotic effects. Microbiotic imbalances can lead to increased (not reduced) inflammation. Moreover, when coeliacs switch to gluten-free diets, many of them gain weight, become insulin resistant, develop systemic inflammation, and show signs of metabolic syndrome. Therefore, going gluten-free is no guarantee of low inflammation and overall health.

Having said that, coeliac disease and non-coeliac gluten sensitivity are serious conditions and should not be taken lightly (here’s how they can be diagnosed). Those who have coeliac disease or are sensitive to gluten should avoid gluten-containing foods and, quite importantly, ensure an adequate intake of all essential nutrients to reduce the risk of deficiencies.

Other critique points

The message in general is oversimplified and encourages removing important food groups from the diet. By removing grains and fruits, many important nutrients, fibre, and phytochemicals will be removed too. Paradoxically, the compounds being removed are linked with disease prevention, including Alzheimer’s. In addition, it isn’t always clear whether Perlmutter is discussing the effects of carbohydrates or gluten, as the language shifts throughout. To add to the confusion around exactly what Perlmutter links to the cause of neurological degeneration, in the diet section of Grain Brain, carbohydrates such as legumes, rice, quinoa, and oats are allowed to be included.

As you would expect in a book focused on carbohydrates, sugar is in the firing line. Perlmutter is an advocate of removing added sugars from the diet, which is certainly a positive step for improving health. However, the message on which sugars to remove is unclear. For example, he believes that fructose, the natural sugar in fruit, should be excluded, as well as all other added sugars. Perlmutter encourages people to eat no more than one portion of fruit per day (and that is only after abstaining for one month).  Fruit is a nutrient-dense, low-energy, high-fibre food, which has been linked with greater risk reduction in some cancers, when compared to vegetables. Fruits are packed with micronutrients and health-benefiting phytochemicals. So encouraging people to remove this whole food group completely is a risky message given the evidence around their protective properties.

And what about wholegrains? Numerous epidemiological studies tell us that the Mediterranean dietary pattern, which is high in wholegrains as well as fruits and vegetables, is linked to a reduced risk of many chronic diseases. There is evidence to suggest that regularly including wholegrains in the diet might be protective against cardiovascular disease, type 2 diabetes and some forms of cancer. There are also findings proposing that, because of the phytoestrogens found in whole grains, high intakes can reduce the increased risk of cognitive decline and neurodegenerative disease associated with menopause in women. Because the Mediterranean diet is high in fibre and phytochemicals, it is a dietary pattern which has been widely encouraged. One recent study even went as far as to quantify the benefit of following a Mediterranean diet, reporting that those who do might live up to two years longer.

Another area of the science which Perlmutter did not include is deficiency. With wholegrains thought to protect against obesity, diabetes, CVD and certain cancers because of their fibre content as well as the antioxidant properties, it is important to consider the evidence before removing this important food group. In general, Western diets lack fibre and many people in the UK do not met the revised 30 grams per day recommendation. Whilst fruit and vegetables contain fibre, they also contain water, making wholegrains, beans, and pulses a more condensed source. In addition, fortified bread and cereals have become a large contributor for B vitamins and iron in the UK population.

Therefore, before removing anything, it is critical to consider replacing these nutrients in the diet, particularly in high-risk populations. For example, B vitamins and iron are consistently linked with improved mental function including depression, cognitive impairment in the elderly, and cognitive performance in young adults.

A grain of truth

Given the controversy Grain Brain has caused, the criticism it has received from the scientific community (a quick google search will find you several less-than-favourable reviews), we contacted Perlmutter to ask him why he thought his peers do not fully his support his theory, and why guidance on wholegrain consumption doesn’t appear to be changing any time soon. Perlmutter told us: “This is likely because grains are so deeply entrenched into our culture and modern lives. In addition, there is a long-held belief that the brain can only run on glucose.”

Perlmutter is right, in a broad sense, that the brain can run on alternative fuels besides glucose. However, ketogenic dieting is not proven to be safe for absolutely everyone, always. Deficiency risks, individual tolerance, and personal genetics need to be considered too. This is confirmation that Perlmutter based his book primarily on belief, selectively citing studies and not including the full body of scientific evidence.

WARNING: The side effects of ketogenic dieting include metabolic acidosis, dehydration, digestive problems, abdominal pain, vomiting, diarrhoea, constipation, amenorrhea, muscle cramps, hypoglycaemia, dizziness, and fainting. Besides metabolic acidosis, other metabolic problems include: hypercholesterolemia, hyperuricemia, carnitine deficiency, hypocalcaemia, and hypomagnesemia.

To read or not to read

No need to read. There are other books available which are better referenced, and do not confuse high-carbohydrate foods with high-glycaemic foods. If you do read, do so with a very large pinch of salt (or gluten if you aren’t sensitive!).

Our verdict

To read or not to read? NO NEED TO READ

Entertainment value: 3/5

Impartiality: 1/5

Context and completeness: 1/5

New discoveries: 1/5

Readability: 4/5

Scientific references: 1/5

Our total score: 2/5

Find this book: UK Version | US Version | CA Version



Alex Ruani leads the research division at The Health Sciences Academy, where she and her team make sense of complex scientific literature and translate it into easy-to-understand practical concepts for students. She is a Harvard-trained scientific researcher who specialises in cravings and appetite neurobiology, nutrition biochemistry, and nutrigenomics. Besides investigating and teaching the latest advances in health and nutrition science, Alex makes it easier to be smarter with her free Science Catch-ups every other Thursday.
Connect with Alex via email.

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  • Crysti Couture

    Reply Reply March 24, 2016

    Excellent review. Thank you for reminding us to think critically and scientifically when reading new literature.

    • Crysti – You’re so welcome, glad you enjoyed it! Critical thinking is a very useful skill to develop in the field of nutrition :-)

    • isma

      Reply Reply August 4, 2016

      Nothing new, you should read “Pure, white and deadly” J. Yudkin.

      • Yes, Isma, Pure, White and Deadly is an “older” book – though it’s in our list of suggested reviews. If there’s any other book you’d like us to review, let us know! :-) Maria (THSA team)

      • isma

        Reply Reply August 5, 2016

        Dear Maria,

        What do you think about that book?

        “Cancer Killing, Suppression and Protection: The Howes Answer To Cancer”

        Thank you very much indeed.


  • JIm mutterspaugh

    Reply Reply March 24, 2016

    I really appreciate the clarity your reviews bring. Some food ideologies are non factual and your information has helped me find them more efficiently.

  • Angela

    Reply Reply March 26, 2016

    What book do you think every person should read? We all want to know how to live the best life we can with the best food choices?

    • Hi Angela, thanks for your question! It would be amazing if we could all live the best life we can with the best food choices. Something to remember is that the best food choices for you may not be the best food choices for someone else, even those with similar genetics. Because most “pop-health” books out there tend to focus on/defend one angle, they may not be applicable to every reader. Luckily, many nutrition scientists are beginning to recognise that everyone is different, and the fields of metabolomics, nutrigenomics, nutrigenetics, toxicology, and even sports nutrition are moving towards a more personalised approach. In terms of furthering your knowledge to help others make the best food choices for THEM (because it’s different for everyone), our courses are designed to help with that and by looking at our course curricula you will get a sense for how you might be able to help others develop personalised plans. As for reading materials, I would say a good (technical, science-heavy) book to start with is Present Knowledge in Nutrition (see here).

      If you’re more of an advanced reader who loves to keep up with the latest, have a look at our Library of downloadable Science Reports, where we investigate new discoveries on nutrition biochemistry, nutritional genetics and eating psychology, to name a few (a premium subscription is required):

      Of course, if you haven’t already, you’re welcome to join our starter nutrition course (it’s free), which covers basic principles from which you can build your knowledge later on and has a good list of further reading materials for you:

      If you have any other questions, don’t hesitate to contact our Lerner Services team (“Contac Us” link in the menu above) who will be happy to help you :-)

      Maria (THSA Team)

  • Fleur

    Reply Reply March 29, 2016

    Excellent review and another reason why I love studying with The Health Sciences Academy. There is so much confusing information about there and so much of it is just opinion. But you clear things up for us and provide us with science and facts, and that means more than anything. Thank you again and keep up the great work!

  • Salome

    Reply Reply April 27, 2016

    I have been convinced by the diets and lives of my grandparents, and more recently by the weightloss, increased energy, brain clarity not to mention the decrease in aches and pains etc of people that have changed to eating Low Carb (carbs from veg and limited fruit) medium protein and High Fat (actually Healthy Fat). The fat intake its probably the same as what people would consume on a daily basis anyway with all the hidden fats in crisps, crackers, pastries, cakes, etc etc. with thus style ‘Ketogenic’ diet the fats are olive oil, nut oils, animal fats, avo, butter etc (also included nuts and seeds. A number of people I know have had a decrease in their cholesterol as well. Not arguing with the review of this book but have also looked at the science behind the Banting style LCHF diet. Must clarify though that although technically all veg as in your spinach example are high carb they have no or low glycemic effect and this type of ‘low carb’ diet is consequently high in most veg.

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