The Best Diet For High-Performing Brain Health Plus The One Food Ingredient You Must Avoid

We are inundated today with dietary suggestions. It seems like each week a new diet book comes out, each with its own wrinkle on what it means to eat healthy. When I searched Amazon for books tagged with the word diet I got 91,783 results. We have heart-healthy diets, brain health diets, detox diets, fast diets, tummy diets, weight loss diets, vegetarian diets, vegan diets, blood type diets, and paleo diets.

Clearly some of these books are very on point and helpful (Dr. Mark Hyman’s 10 Day Detox Diet would be a case in point) but the overall level of white noise certainly creates confusion.


I spoke recently with David Perlmutter, MD, a cutting-edge neurologist, fellow of the American College of Nutrition, and author of the #1 New York Times bestseller, Grain Brain. His opening salvo was a refreshing change of pace: “The notion that there was a brain-smart diet as opposed to a heart-smart diet or immune-boosting diet really is silly. The right diet is what kept humans alive for all these two million years and allowed us to flourish because our genome became refined in response to being targeted specifically with certain foods.”

Adaptations to the human genome, Perlmutter said, “are an exquisitely slow process,” slow enough that our genome today is essentially identical to that of humans who lived 50,000 years ago.

Our genome became adapted over millennia to a certain type of food— essentially what a hunter/gatherer could forage, since that is what was available from the time of the first human up until the first agricultural revolution, around 10,000 BC. This diet was high in lean protein, high in fat (from nuts, seeds, and animals), and very low in carbs. There were no grains or wheat, and they could have only taken advantage of those fruits and vegetables that grew wild, leaving them a short window in which to eat starchy or sweet carbs during the middle to end of summer. “For 99.9 percent of our time on the planet thus far, we did not have access to high-carbohydrate foods or wheat or gluten,” Perlmutter said. “This is brand new.”

And, while our diets changed radically when we settled down and started farming, that was nothing compared with the glut of processed, high-carb, sugary foods that hit the American food market starting in the early 1900s. Oreos and marshmallows came around in the 1910s, candy bars and Wonder Bread in the 1920s, and we devoured them, eating more carbs than ever before in this planet’s history. For the first time ever, we ate food without nutrition and our bodies revolted.


While the calories with no nutrition certainly hindered our health, the more damning revolt took place on an infinitesimally small scale, playing out in our DNA. While the genome changes at a sub-glacial pace, the expression of the genome changes rapidly—this is the crucial insight of epigenetics. To paraphrase Perlmutter, our genetics are like the keys of the piano, and epigenetics are how the piano is played.

What determines the tune that is being played here? Food (and the information therein) provides the sheet music our bodies are playing. When we choose to get aerobic exercise and eat the right foods (and, just as importantly, avoid the wrong ones) our bodies will react power­fully. “When you’re concentrating, for example, on eating rich, nutrient-dense, colorful, above-ground vegetables,” Perlmutter said, “those are powerfully influential in terms of their epigenetic aspects by turning on various genes like the NRF2 genes that code for powerful antioxidants and for powerful ways of reducing inflam­mation.”

This is, of course, in stark contrast to what is happening now in the bodies of most Americans. A diet higher in carbs and sugar (i.e., the “low-fat diet” we are all supposed to be on according to the USDA) produces higher blood sugar. Higher blood sugar leads to inflammation and increased free radical production. “That’s the cornerstone of this,” Perlmutter said. “Elevated blood sugar binds to proteins causing a process called glycation and a glycated protein can produce as much as a 50-fold increase in the production of free radicals.” This is maladaptive epigenetics at work.


Because Perlmutter is a neurologist, his primary area of concern is brain health. This interest is intensely personal as his father, a retired brain surgeon, is now fighting Alzheimer’s disease. “The accepted paradigm right now is live your life, come what may, and then there’ll be a pill to fix whatever you’ve developed,” he said. “There is no pill at all for treating Alzheimer’s disease. How it tugs at your heartstrings to know that it is preventable if only people have this information.”

It surprised me to learn that, at its root, Alzheimer’s is an inflammatory condition, just like arthritis would be in your knee or elbow. Anything that can be done to keep inflammation to a minimum in the body will go a long way toward preventing Alzheimer’s and even to see improvements in people who currently have the disease. “That’s the current leading edge of research,” Perlmutter said.

And, as much as Alzheimer’s is personally devastating to those afflicted and their loved ones, we are also spending an incredible amount on its treatment—200 billion dollars a year, roughly the GDP of Ireland. That’s twice what we are spending for heart disease patients and triple what we’re spending on cancer care.

So what are the risk factors for Alzheimer’s? Inflammation, as mentioned previously. Extra body fat—one study followed individuals for 30 years and did a triceps skinfold measurement to measure fat. The individuals with the highest levels of fat had triple the risk of developing Alzheimer’s.

Sleep interruption is another risk factor, and much of our sleep inter­ruption is caused by sleep apnea. And what causes sleep apnea? Obesity is one big contributor and obesity comes from a diet high in carbs and low in exercise.

Lastly, diabetes is, as you might expect, a player in this. And this is where our low-fat diet really comes back to haunt us. In 1992, the government told us to eat a low-fat or no-fat diet, thinking that dietary fat led to heart disease. Within 10 years, rates of diabetes tripled (in hindsight, this was predictable). Type 2 diabetes doubles the risk of Alzheimer’s.

And how about Parkinson’s? “The [ultra-low-carb] ketogenic diet was actually studied in the Journal of Neurology, the most well-respected neurology journal perhaps on the planet. They found that the ketogenic diet was the most effective diet, bar none, in terms of improving actual symptoms of Parkinson’s disease,” Perlmutter said. “It all comes back to eating too many carbs and not getting enough exercise.”


Gluten seems to be the villain in a large percentage of the dietary storylines lately, and this one is no exception. Why is that? The short answer is that, while the number of people who have a true autoimmune reaction to gluten vis-à-vis celiac disease is low, 30 to 40 percent of us have neurological problems such as headaches, depression, and dementia that are related to gluten. Gluten represents carbs of course, but more importantly it also contributes significantly to inflammation in a large percentage of people who eat it.

This insight comes thanks to the pioneering work of the celiac researcher Alessio Fasano, MD, who noted that gluten stimulates the intestinal lining cells (among others) to make a protein called zonulin. Zonulin opens the “gap junctions” in the intestines, making the intestine more permeable. This lets proteins out into the rest of our body, where they shouldn’t be, and the resulting challenge to our immune system creates inflammation.

“This is a very, very big deal,” Perlmutter said. “The validation of all this comes from the tens of thousands of individuals who are reporting on my Facebook site and in the gluten-free websites about remarkable if not miraculous improvements in devas­tating situations from which they have suffered sometimes for their entire lifetimes and now, suddenly, they’ve gotten through it.”


Whatever dietary path you’ve walked until this point, the good news is that it’s never too late to take action to protect your health. On the specific subject of brain health, Perlmutter mentions neurogenesis: “This is a process that never ends in your entire lifetime. If you’re 90 years old, your brain is still cranking out new brain cells—who knew?”

You can actually turn on the genes to enhance that process through aerobic exercise and eating omega-3 fats (specifically the DHA form found in fish and other foods). Perlmut­ter’s main focus is to put people on a preventitive program today so their brains will be functional tomorrow.

So what does this healthy way of eating look like? When you cut out carbs to a large degree, you’re going to be getting most of your calories from fat and protein. (I asked Perlmutter what he considered a good level of carb consumption—how about 75 grams a day? Since many Americans eat 300 grams of carbs a day, that would be a 75 percent reduction. His response: “Cutting down to 75 grams of carbs a day is fantastic.”) There’s no need to be concerned about eating a lot of fat and protein, provided you are getting the right fat and protein.

Perlmutter encourages the “good fats in extra virgin olive oil, avocado, nuts, cheese, wild fish, and grass-fed beef, not the modified, damaged fats that are like coffin nails as they relate to brain health.” As I discovered during my own recent low-carb odyssey, this still means eating a lot of vegetables. A lot. Vegetables are so low in calories that you are eating mostly vegetables by volume, but your calories are coming mostly from the olive oil, meat, cheese, nuts, and so on. For example, 2 cups of lettuce has 10 calories, whereas a tablespoon of olive oil that would go on top of the salad has 120. So, while the olive oil seems almost like an afterthought and you’ll be crunching away on the lettuce for a while, the olive oil has over 90 percent of the calories. (For more specific parameters on the eating plan, check out Grain Brain.)

If you’re wondering about specific items, you can look at the overall carb count and the glycemic index of that food. Foods with a high glycemic index will cause major peaks and valleys in your blood sugar as your body burns through them like dry leaves. Dietary fats, on the other hand, burn “like an oil lamp, slow and steady.”

So the best diet in the end is the one we had been eating all along—fish, meat, nuts, seeds, vegetables, and fruits. This diet, the only diet we have had up until recently, has seen us through two million years and is still as effective as ever.

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