The Diet We Were Designed to Eat

There are three broad theories about evolution and food. One is that humans have become adapted to grains and other products of the agricultural revolution over the last 10,000 years. Two is the paleo view “that 10,000 years is a blink of an evolutionary eye, and that humans are adapted to paleolithic diets with a lot of lean meat,” but why stop there? The third theory is that the last 200,000 years “is a minute of the evolutionary year” when we were mostly Stone Age humans and represents just the last 1 percent of the roughly 20 million years we’ve been evolving since our common great ape ancestor. So, What Is the “Natural” Human Diet?

During our truly formative years, which one might say was the first 90 percent of our existence, our nutritional requirements reflected an ancestral past in which we ate mostly leaves, flowers, and fruits, with some bugs thrown in, thanks to wormy apples, to get our vitamin B12. “For this reason, another approach that might improve our understanding of the best dietary practices for modern humans is to focus attention not on the past but rather on the here and now; that is, on study of the foods eaten by the closest living relatives of modern humans,” given the bulk of our ancestral diets and “the lack of evidence supporting any notable diet-related changes in human nutrient requirements, metabolism, or digestive physiology” compared to our fellow great apes.

This could explain why fruits and vegetables are not only good for us but are vital to our survival. Indeed, we’re one of the few species so adapted to a plant-based diet that we could actually die from not eating fruits and vegetables, from the vitamin C-deficiency disease, scurvy. Most other animals simply make their own vitamin C, but why would our body waste all that effort when we evolved hanging out in the trees just eating fruits and veggies all day long?

Presumably, it’s not a coincidence that the few other mammals unable to synthesize their own vitamin C—including guinea pigs, some bunny rabbits, and fruit bats—are all, like us great apes, strongly herbivorous. Even during the Stone Age, data from rehydrated human fossilized feces tell us we may have been getting up to ten times more vitamin C and ten times more dietary fiber than we get today. The question is: Are these incredibly high-nutrient intakes simply an unavoidable by-product of eating whole, plant foods all the time, or might they actually be serving some important function, like antioxidant defense?

Plants create antioxidants to defend their own structures against free radicals. The human body must defend itself against the same types of pro-oxidants, so we too have evolved an array of amazing antioxidant enzymes, which are effective but not infallible. Free radicals can breach our defenses and cause damage that accumulates with age, leading to a variety of disease-causing and ultimately fatal changes. This is where plants may come in: “Plant-based, antioxidant-rich foods traditionally formed the major part of the human diet,” so we didn’t have to evolve that great of an antioxidant system. We could just let the plants in our diet pull some of the weight, like giving us vitamin C so we don’t have to be bothered to make it ourselves. Using plants as a crutch may well have relieved the pressure for further evolutionary development of our own defenses. That is we’ve become dependent on getting lots of plant foods in our diet, and when we don’t, we may suffer adverse health consequences.

Even during the Stone Age, this may not have been a problem. Only in recent history did we start giving up on whole plant foods. Even modern-day paleo and low-carb followers may be eating more vegetables than those on standard Western diets. There’s a perception that low-carbers are chowing down on the three Bs—beef, bacon, and butter—but that’s only a small minority. What they are eating more of is salad. Indeed, according to an online low-carb community, the number one thing they said they were eating more of was vegetables. Great! The problem isn’t people wanting to cut their carb intake by swapping junk food for vegetables. The concern is the shift to animal-sourced foods. “Greater adherence to [a low-carb diet] high in animal sources of fat and protein was associated with higher all-cause and cardiovascular mortality post-MI,” or after a heart attack, meaning they cut their lives short.

If there’s one takeaway from our studies of ancestral diets, perhaps it’s that “diets based largely on plant foods promote health and longevity.”


For more on the paleo and low carb diets, see:

If you were fascinated by how we can take advantage of plant defense mechanisms, check out my videos Appropriating Plant Defenses and Xenohormesis: What Doesn’t Kill Plants May Make Us Stronger.

How many antioxidants should we shoot for? See:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Change Your Diet; Change Your Microbiome

If whatever gut flora enterotype we are could play an important role in our risk of developing chronic diet-associated diseases (see What’s Your Gut Microbiome Enterotype?), can we alter our gut microbiome by altering our diet? Yes. Indeed, diet can rapidly and reproducibly alter the bacteria in our gut, as I discuss in my video How to Change Your Enterotype.

Concern has been growing that recent lifestyle trends––most notably the high-fat and high-sugar “Western diet”––have altered the composition and activity of our resident gut flora. “Such diet-induced changes to gut-associated microbial communities are now suspected of contributing to growing epidemics of chronic illness in the developed world,” yet it has remained unclear how quickly our gut bacteria could respond to dietary change. So, researchers prepared two diets: a “plant-based diet” rich in grains, beans, fruits, and vegetables, and an “animal-based diet” composed of meats, eggs, and cheeses. Neither diet contained refined sugars, as the researchers just wanted to test diets consisting of plant versus animal products. Within just one day of the animal-based diet hitting the gut, there was a significant shift.

What happens when you put a lifelong vegetarian on an animal-based diet? The vegetarian’s baseline microbiota was dominated by Prevotella, unlike everyone else eating a more standard American diet, who had large Bacteroides populations. Remarkably, the animal-based diet inverted the vegetarian’s Prevotella-to-Bacteroides ratio, causing the Bacteroides to outnumber the Prevotella within just four days on the animal-based diet. The entire gut flora got turned on its head and got completely reversed.

The fact that our gut can so rapidly switch between herbivorous and carnivorous functional profiles is probably a good thing in terms of evolution. If you bring down a mammoth and eat meat for a couple of days before switching back to plants, you want your gut to be able to deal with it. This flexibility is manifest in the diversity of human diets to this day, but what is the healthier state to be in most of the time?

Researchers looked at a number of different factors, such as the amount of short-chain fatty acids produced. Short-chain fatty acids, like acetate and butyrate, function to suppress inflammation and cancer, and our gut flora, when on plant-based diets, produce more of these than when on animal-based diets.

Other microbial metabolites, such as secondary bile acids, do the opposite, promoting the development of cancer. With a significant increase in bacterial enzyme activity to create these secondary bile acids on an animal-based diet, it’s no surprise there’s a significant increase in carcinogens like DCA, a secondary bile acid known to promote DNA damage and liver cancer. Microbial enzyme activity producing the rotten egg gas, hydrogen sulfide, also shoots up on an animal-based diet, which stinks because it’s stinky and also because it damages DNA and has been implicated in the development of inflammatory bowel diseases like ulcerative colitis. Hydrogen sulfide is made by pathogens such as Bilophila wadsworthia and is increased on the animal-based diet, again within just days of adopting it, supporting the link between diet and the outgrowth of microorganisms capable of triggering inflammatory bowel disease. Conversely, the only pathogen you see more of on a plant-based diet is just a virus that infects spinach.


Do you know What’s Your Gut Microbiome Enterotype?

See more about gut microbiomes:

I’ve produced a series about the epic fermentation battle in the gut between protein and carbs that offers lots of insight on why it matters who we have living down there:

And check out some other videos on inflammatory bowel disease:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Plant-Based Diets Put to the Test for Diabetes

My Why Is Meat a Risk Factor for Diabetes? video shows how meat may play a role in increasing the risk of diabetes, and How May Plants Protect Against  Diabetes? and Plant-Based Diets and Diabetes discuss the potential protective role of healthy plant foods. But plant-based diets not only appear to guard against getting diabetes in the first place, they may successfully treat the disease better than the diabetic diets patients typically are placed on, benefiting both weight and cholesterol.

Diets based on whole plant foods can result in significant weight loss without limiting portion size or counting calories, because plant foods tend to be so calorically dilute. In my video Plant-Based Diets for Diabetes, you can see the volume of 100 calories of broccoli, tomatoes, and strawberries compared to 100 calories of chicken, cheese, or fish. People just can’t seem to eat enough of the plant foods to compensate for the calorie deficit, so they lose weight eating whole plant foods.

Most importantly, a plant-based diet works better. A plant-based diet beat out the conventional American Diabetes Association diet in a head-to-head, randomized, controlled clinical trial, without restricting portions and without calorie- or carb-counting. A review of all such studies found that those following plant-based diets experience improved reductions in blood sugars, body weight, and cardiovascular risk, compared with those on diets including animal products.

Cardiovascular risk is what kills diabetics the most. They’re more likely to get strokes, more likely to suffer heart failure. In fact, “[d]iabetes has been proposed as a coronary heart disease risk equivalent, which means diabetic patients without a history of coronary disease have an equivalent risk to that of nondiabetic individuals with confirmed heart disease.”

A newer study used a technique to actually measure insulin sensitivity. It improved on both diets in the first three months, but then the vegetarian diet pulled ahead. The researchers also found that the LDL cholesterol fell significantly in the vegetarian group. Indeed, that’s what we see when people are put on plant-based diets: Cholesterol comes down so much it can actually reverse the atherosclerosis progression—that is, reverse the progression of heart disease.

We know about the beneficial effect of a vegetarian diet on controlling weight, blood sugars, cholesterol, insulin sensitivity, and oxidative stress compared to conventional diabetic diets, but what about quality of life and mental health? How did people feel after making such a dramatic change in their diets? In a randomized, controlled trial, study subjects were assigned either to a plant-based diet group or a control group. The plant-based group ate vegetables, grains, beans, fruits, and nuts with animal products limited to a maximum of one daily portion of low-fat yogurt. The control group followed an official diabetes diet.

Quality of life improved on both diets in the first three months, but, within six months, the plant-based group clearly pulled ahead. The same results were seen with depression scores: They dropped in both groups in the first three months, but started to rebound in the control group.

The bottom line is that the more plant-based diet “led to a greater improvement in quality of life and mood. Patients consuming a vegetarian diet also felt less constrained than those consuming the conventional diet.” People actually felt the conventional diabetic diet was more restrictive than the plant-based diet. Disinhibition decreased with a vegetarian diet, meaning those eating vegetarian were less likely to binge, and the subjects in the vegetarian group tended to feel less hungry. All of this helps with sustainability in the long term, which is, of course, critical for any dietary change. So, not only do plant-based diets appear to work better, but they may be easier to stick to. And, with the improvement in mood, patients may exhibit desired improvements not only in physical, but also in mental, health.


For those seeking a deeper understanding of what diabetes really is and what causes it, check out How Not to Die from Diabetes and this series of videos:

Thankfully, not only can diabetes be reversed, but so can some of its complications. See Can Diabetic Retinopathy Be Reversed? and, for diabetic neuropathy, my live annual review From Table to Able: Combating Disabling Diseases with Food.

Of course, preventing it is better:

There are some foods that may increase the risk:

And others that may help:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations: