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How our evolution has shaped our dietary needs

One thing that bothered me while I was studying nutrition in graduate school was that the majority of nutrition professionals had little biology background.  I was not only older than my classmates (and most of the professors) but had been steeped in the evolutionary aspects of biology for many years, both as a biology teacher and as a wife and mother of biologists.  I knew that humans had spent most of their time on earth as hunter-gatherers, in fact 99.6% of the time since the genus Homo appeared ~2.4 million years ago. The hunter-gatherer period encompasses all but the last 10,000 years of our existence.  The genetic adaptations to our food environment occurred during the hunter-gatherer period, with only minor changes occurring after the advent of agriculture 10,000 years ago.

The diet of a person during that long time span before agriculture began varied, of course, depending on where he lived.  Modern humans arose on the subtropical savannahs of Africa and migrated to all parts of the earth.  In general, however, hunter-gatherer societies obtained at least 50% of their sustenance from animal foods.  This high reliance on animal foods plus the relatively low carbohydrate content of plant foods means that the most plausible percentages of total energy would be 19–35% for dietary protein, 22–40% for carbohydrate, and 28–58% for fat (Cordain et al, 2000). Game and wild plant foods contain more protein, less fat, more fiber, and more micronutrients per unit weight than do modern supermarket foods (Eaton et al, 1997).  Even though wild animals have a lower fat content associated with their muscles, our human ancestors did not limit themselves to lean muscle meat; doing so, in light of their high animal source diet, would have meant that they consumed a toxic amount of protein.  Instead they coveted the fatter parts of the animals—organ meats, brains, bone marrow, etc. (Cordain et al, 2000).  The meat of game animals living on wild plants and grass also contains much higher amounts of omega-3 fatty acids than does the meat of modern domesticated animals.  Furthermore, animal foods for our ancestors also included a large quantity of fish and shellfish as well as small mammals, reptiles, amphibians, insects, snails, etc.  Many of these animals were no doubt collected along with foraged plant food, which consisted mainly of vegetables, fruit, nuts and maybe a smattering of grain.

We are adapted to this hunter-gatherer diet, which sustained us for millennia.  Prehistoric humans had robust skeletons and were about as tall as we are today in developed countries.  With the advent of agriculture approximately 10,000 years ago humans went from a diet based largely on animal foods to one based largely on grain.  Archeological sites reveal that people during this period were shorter and showed signs of bone loss (Cohen, 1989; Larsen, 2003) compared to their hunter-gatherer ancestors.  There are many factors involved in this seeming decline in health—increases in population, crowding, living in close proximity with animals and the resultant transmission of diseases, but certainly the change in diet was a major factor.  There has not been enough time since the advent of agriculture and grain-based diets for a major change in our genetics, although genetic modifications for eating grains is beginning to be discovered using advanced genetic techniques and information from the human genome project.  Evidence for multiple copies of the salivary amylase gene in high starch eating Asians, and a gene variant that is important for breaking down fats in plant foods in Europeans and Middle Easterners may reflect an adaption to agriculture (Hancock et al, 2010). Along with the growing of grains came the domestication of certain animals for use as food, mainly cattle, sheep/goats, pigs and chickens, introducing new foods made from milk into our diets, and subsequently the retention of the lactase gene into adulthood in cattle-raising populations.  Until about 100 years ago these novel foods sustained us because they were grown locally or raised on their natural diets, eaten fresh and whole, or preserved in ways that enhance nutrient content.  Grains went through many steps (soaking, sprouting, long proofing) before they were deemed fit for consumption.

A little more than 100 years ago began the industrialization of the food supply.  The roller mill was invented, meaning we could have white flour.  Then, as the need for candles waned with the advent of electricity, vegetable oil was turned into Crisco and oleomargarine and touted as healthier than butter.  Sugar consumption climbed until it is now in the stratosphere, and food has become ultra-pasteurized, taken apart and put back together, stripped of nutrients (they spoil) and “fortified” with all manner of industrial waste masquerading as nutrients.  Farm animals are raised in deplorable conditions, fed unnatural diets, and their meat and eggs are frequently contaminated with pathogenic bacteria as a result.  Even fruits and vegetables have been modified to keep and ship well instead of taste good and be nutrient dense.  And how does this modern supermarket diet compare to the one we evolved on?  Remember, our ancestors would have gotten 19-35% of their energy from protein, 22-40% from carbohydrate, and 28-58% from fat. In the United States, the third National Health and Nutrition Survey showed that among adults aged ≥20 y, protein contributed 15.5%, carbohydrate 49.0%, fat 34.0%, and alcohol 3.1% of total energy intake (McDowell, 1994).  Therefore, the range of percentages for carbohydrate and protein in most hunter-gatherer diets falls outside the average value for Western diets, and even more so for the USDA recommended healthy diets (15% of energy from protein, 55-65% from carbohydrate, and 20-35% from fat). Furthermore, the types of plant and animal foods that together comprise the macronutrient composition of hunter-gatherer diets are substantially different from those commonly consumed by Westernized societies. In the United States, the 1987–1988 National Food Consumption Survey indicated that cereal grains contributed 31%, dairy products 14%, beverages 8%, oils and dressings 4%, and discretionary sugar and candy 4% of the total energy intake for all individuals. Virtually none of these foods would have been available to hunter-gatherers. Cereal grains represent the highest single food item consumed on the basis of energy content in both the United States and the rest of the world (Cordain et al, 2000).

Is it any wonder that we have such high rate of chronic disease?  There is a small but growing group of people, e.g. Primal Body Primal Mind, Mark’s Daily Apple, who believe that we should adopt a diet more like our ancestors would have eaten.  This eating plan would eliminate all grain and dairy products, and of course processed foods of any kind.  Many people have found markedly better health when switching to this type of eating.  However, Weston A. Price found healthy traditional cultures consuming properly prepared grains and dairy products.  But a generalized message might be that we would all be better off cutting back on carbohydrates to some extent, making sure we have adequate complete protein from animal sources, and increasing our natural fat intake.  By the way, vegetable oils, with the exception of olive and coconut, are not natural fats.  In order to be extracted from seeds they must be highly processed.  Our ancestors would never have eaten them. We are all individuals in our nutrient needs and body tolerances.  If someone is sensitive to grains or dairy products he/she may well regain healthy be eating a more “cave man” diet.  If not, a diet of whole natural foods, which includes some grain and dairy, may be the healthiest for them.  It’s worth experimenting!

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