It's tempting to call David Perlmutter's dietary advice radical.

The neurologist and president of the Perlmutter Health Center in Naples, Fla., believes all carbs, including highly touted whole grains, are devastating to our brains.

He claims we must make major changes in our eating habits as a society to ward off terrifying increases in Alzheimer's disease and dementia rates.

And yet Perlmutter argues that his recommendations are not radical at all. In fact, he says, his suggested menu adheres more closely to the way mankind has eaten for most of human history.

What's deviant, he insists, is our modern diet. Dementia, chronic headaches, depression, epilepsy and other contemporary scourges are not in our genes, he claims. "It's in the food you eat," Perlmutter writes in his bestselling new book, Grain Brain: The Surprising Truth About Wheat, Carbs, and Sugar — Your Brain's Silent Killers. "The origin of brain disease is in many cases predominantly dietary."

How We Got Here

Perlmutter's book is propelled by a growing body of research indicating that Alzheimer's disease may really be a third type of diabetes, a discovery that highlights the close relationship between lifestyle and dementia. It also reveals a potential opening to successfully warding off debilitating brain disease through dietary changes.

(MORE: Is Alzheimer's Really a Type of Diabetes?)

Perlmutter says we need to return to the eating habits of early man, a diet generally thought to be about 75 percent fat and 5 percent carbs. The average U.S. diet today features about 60 percent carbs and 20 percent fat. (A 20 percent share of dietary protein has remained fairly consistent, experts believe.)

Some in the nutrition and medical communities take issue with Perlmutter's premise and prescription. Several critics, while not questioning the neurological risks of a high-carb diet, have pointed out that readers may interpret his book as a green light to load up on meat and dairy instead, a choice that has its own well-documented cardiovascular health risks.

"Perlmutter uses bits and pieces of the effects of diet on cognitive outcomes — that obese people have a higher risk of cognitive impairment, for example — to construct an ultimately misleading picture of what people should eat for optimal cognitive and overall health," St. Catherine University professor emerita Julie Miller Jones, Ph.D., told the website FoodNavigator-USA.

Grain Brain does delve deeply into the neurological effects of dietary sugar. "The food we eat goes beyond its macronutrients of carbohydrates, fat and protein," Perlmutter said in a recent interview with Next Avenue. "It's information. It interacts with and instructs our genome with every mouthful, changing genetic expression."

Human genes, he says, have evolved over thousands of years to accommodate a high-fat, low-carb diet. But today we feed our bodies almost the opposite, with seemingly major effects on our brains. A Mayo Clinic study published earlier this year in the Journal of Alzheimer's Disease found that people 70 and older with a high-carbohydrate diet face a risk of developing mild cognitive impairment 3.6 times higher than those who follow low-carb regimens. Those with the diets highest in sugar did not fare much better. However, subjects with the diets highest in fat were 42 percent less likely to face cognitive impairment than the participants whose diets were lowest in fat.

Further research published in the New England Journal of Medicine in August showed that people with even mildly elevated levels of blood sugar — too low to register as a Type 2 diabetes risk — still had a significantly higher risk of developing dementia.

(MORE: Fiftysomething Diet: Boosting Your Longevity Odds)

"This low-fat idea that's been drummed into our heads and bellies," Perlmutter says, "is completely off-base and deeply responsible for most of our modern ills."

Turning to Nutrition, Not Pills

This fall, the federal government committed $33.2 million to testing a drug designed to prevent Alzheimer's in healthy people with elevated risk factors for the disease, but "the idea of lifestyle modification for Alzheimer's has been with us for years," Perlmutter says, and it's cost-free.

The author hopes his book and other related media on the diet-dementia connection will inspire more people to change the way they eat. "Dementia is our most-feared illness, more than heart disease or cancer," Perlmutter says. "When you let Type 2 diabetics know they're doubling their risk for Alzheimer's disease, they suddenly open their eyes and take notice.

"People are getting to this place of understanding that their lifestyle choices actually do matter a whole lot," he says, "as opposed to this notion that you live your life come what may and hope for a pill."

As we learn more about the brain's ability to maintain or even gain strength as we age, Perlmutter believes, diet overhauls could become all the more valuable.

"Lifestyle changes can have profound effects later in life," he says. "I'm watching people who'd already started to forget why they walked into a room change and reverse this. We have this incredible ability to grow back new brain cells. The brain can regenerate itself, if we give it what it needs."

(MORE: 3 Easy Ways to Whip Your Brain Into Shape)

What it needs most of all, Perlmutter says, is "wonderful fat." There's no room in anyone's diet for modified fats or trans fats, he says, but a diet rich in extra-virgin olive oil, grass-fed beef and wild fish provides "life-sustaining fat that modern American diets are so desperate for."

Too few of us understand there's "a big difference between eating fat and being fat," he says. People who eat more fat tend to consume fewer carbs. As a result, they produce less insulin and store less fat in their bodies.

Change We Ought to Believe In

Changing minds, however, is an uphill climb. "The idea that grains are good for you seems to get so much play," he says. "But grains are categorically not good for you," not even whole grains.

"We like to think a whole-grain bagel and orange juice makes for the perfect breakfast," Perlmutter continues. "But that bagel has 400 calories, almost completely carbohydrates with gluten. And the hidden source of carbs in this picture is that 12-ounce glass of fresh-squeezed orange juice. It has nine full teaspoons of pure sugar, the same as a can of Coke. It's doing a service with Vitamin C, but you've already gotten 72 grams of carbs.

"It's time to relearn," he says. "You can have vegetables at breakfast — the world won't come to an end. You can have smoked salmon, free-range eggs with olive oil and organic goat cheese and you're ready for the day. And you're not having a high-carb breakfast that can cause you to bang on a vending machine at 10 a.m. because your blood sugar is plummeting and your brain isn't working."

(MORE: How You Can Make Your Brain Smarter Every Day)

Changing one's diet is a challenge, he acknowledges. Giving up the gluten found in most carbs makes it even tougher. "The exact parts of the brain that allow people to become addicted to narcotics are stimulated by gluten," Perlmutter points out. "People absolutely go through withdrawal from gluten. It takes a couple of weeks."

But the change is worth making, he says, at any age.

"Nutrition matters," Perlmutter says. "The brain is more responsive to diet and lifestyle than any other part of the body and until now it's been virtually ignored. We load up on medications when our mood is off, we hope for an Alzheimer's disease pill when we get older. I submit that we need to take a step back and ask, 'Is this really how we want to treat ourselves?'"