Our epidemics of dietary disease have prompted a great deal of research into what humans are meant to eat for optimal health. In 1985, an influential article was published proposing that our chronic diseases stem from a disconnect between what our bodies evolved eating during the Stone Age during the last two million years, and what we’re stuffing our face with today, advocating for a return towards a hunter-gatherer type diet of lean meat, fruits, vegetables, and nuts.

Though it may be reasonable to assume our nutritional requirements were established in the prehistoric past, the question of which prehistoric past remains. Why just the last two million? We’ve been evolving for 25 million years since our common great ape ancestor, during which time our nutrient requirements and digestive physiology were set down, and therefore probably little affected by our hunter-gatherer days at the tail end. So what were we eating for the first 90% of our evolution? What the rest of the great apes ended up eating: over 95% plants.

This may explain why we’re so susceptible to heart disease. For most of human evolution, cholesterol may have been virtually absent from the diet. No bacon, butter, trans fats, and massive amounts of fiber, which pulls cholesterol from the body. Now this could have been a problem, since our body needs a certain amount of cholesterol, so our bodies didn’t just evolve to make cholesterol, but to preserve it, recycle it. Our bodies evolved to hold onto cholesterol. And so if you think of the human body as a cholesterol-conserving machine, and plop it into the modern world of bacon/eggs/cheese/chicken/pork/pastry, well then, no wonder artery-clogging heart disease is our #1 cause of death. What used to be so adaptive for 90% of our evolution–holding on to cholesterol at all costs since we aren’t getting much in our diet–is today maladaptive, a liability leading to the clogging of our arteries. Our bodies just can’t handle it.

As the editor-in-chief of the American Journal of Cardiology noted 25 years ago, no matter how much fat and cholesterol carnivores eat, they do not develop atherosclerosis. You can feed a dog 500 eggs worth of cholesterol and a stick of butter and they just wag their tail; their bodies evolved from wolves, and are used to eating and getting rid of excess cholesterol, whereas within months, a fraction of that cholesterol can start clogging the arteries of animals adapted to eating a more plant-based diet.

Even if our bodies were designed by natural selection to eat mostly fruit, greens and seeds for 90% of our evolution, why didn’t we better adapt to meat-eating in the last 10%, during the Paleolithic? We’ve had nearly two million years to get used to all that extra saturated fat and cholesterol. If a lifetime of eating like that clogs up nearly everyone’s arteries, why didn’t the genes of those who got heart attacks die off and get replaced by those who could live to a ripe old age with clean arteries, regardless what they ate?

Because most didn’t survive into old age; they didn’t live long enough to get heart attacks. When the average life expectancy is 25, then the genes that get passed along are those that can just get us to reproductive age by any means necessary, and that means not dying of starvation. So the higher the calorie foods, the better. So eating lots of bone marrow and brains, human and otherwise, would have a selective advantage, as would discovering a time machine stash of Twinkies, for that matter. If we just have to live long enough to get our kids to puberty to pass along our genes, then we don’t have to evolve any protections against the ravages of chronic disease.

To find a population nearly free of chronic disease in old age, we don’t have to go back a million years. In the 20th century, networks of missionary hospitals in rural Africa found coronary artery disease virtually absent–and not just heart disease, but high blood pressure, stroke, diabetes, common cancers, and on down the list.

In a sense, these populations in rural China and Africa were eating the type of diet we’ve been eating for 90% of our last 20 or so million years–a diet almost exclusively of plant foods. How do we know it was their diet that protected them, and not something else?

In the 25-year update to their original Paleo paper, the authors tried to clarify that they did not then, and do not now, propose that people adopt a particular diet just based on what our ancient ancestors ate. Dietary recommendations must be put to the test. That’s why the pioneering research of Pritikin, Ornish, and Esselstyn is so important, showing that plant-based diets can not only stop heart disease, but have been proven to reverse it in the majority of patients. Indeed, it’s the only diet that ever has–perhaps because that’s what we ate through the vast majority of our evolution.

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.

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