Within the ancestral health community, one of the longest standing debates is that over the appropriate macronutrient levels of protein, fat, and carbohydrate which people should eat. Riding the wave of the ancestral movement, has been an amelioration of dietary fats. I wouldn’t say the mainstream has really caught on yet, but the tide is certainly shifting.
Within the paleo community, there is almost the opposite going on, where carbohydrates are shifting somewhere between poison and panacea. Thought-leaders like Gary Taubes and Dr. Robert Lustig, have painted a picture where carbohydrate, probably more so sugar, when eaten to excess can cause severe health issues (type 2 diabetes, heart disease, obesity, etc). On the other hand, a noticeably increasing cadre of bloggers and researchers are doing a 180 degree turn, and placing more emphasis on issues related to carbohydrate deficiency, such as thyroid health.
Caught in the crossfire, are of course the many people trying to improve their health and lives by eating better. What I have observed (through blog comments, and sites like Paleohacks.com), is a not insignificant amount of people who eat diets which hover around near total exclusion of either carbs or fats. You have the 80-10-10′s (ratio of carbs to protein to fat), and then there are the neo-caveman carnivores, emulating a supposed Inuit diet or eating just meat and fat.
Are these types of diets advisable? Are they even appropriate based on what we know of human evolution and physiology? For the second question, each camp will most assuredly and emphatically say, “yes”. In truth, one can easily present various pieces of evidence in a certain light, and come out looking correct. From a broad perspective though, I believe that less extreme diets will probably be appropriate for a larger selection of people, and are more likely to reside within the comfort zone of your own particular genetics.
Why? Well for one, I think that ignorance of cultural behaviors and even of hominid evolution and physiology has lead people to believe in “facts” that are either not entirely accurate, or are somewhat distorted.
For instance, it is commonly believe that the Inuit (poster-child for many low-carb devotees) eat almost no carbohydrate-based food, living almost entirely on meat and animal fat. Their relatively low incidence of degenerative diseases (before westernization) is then used as one leg of a argument supporting zero-carb diets.
The whole truth is that the Inuit ate a fair amount of plant food (when available during the warmer months) and even took to eat the fermented remains of food from the stomachs of caribou. There is a fascinating book called “Plants That We Eat” that explores this aspect of Inuit culture, and Melissa McEwen has done a great review of it.
One phrase that is commonly repeated, is the concept that “there are no essential carbohydrates.” This stems from the fact that the human body can produce glucose through a process called gluconeogenesis. This allows the body to maintain blood-sugar levels during periods of ketosis, low or even zero carbohydrate consumption. However, it does not follow, from a logical sense, that just because carbohydrates aren’t essential for maintaining life, that carbohydrates are not still useful, or even necessary for maintaining optimal health. Some people eating low carb diets and exercising a lot are susceptible to a condition of thyroid dysregulation called “euthyroid sick syndrome”. Anthony Colpo has written extensively about this topic, especially as someone who has compared low carb and higher carb diets during training.
From an evolution and physiological standpoint, I think that the fact that humans evolved to have saliva glands which secrete amylase, an enzyme that catalyses the breakdown of starch into sugars, provides at least cursory evidence that carbohydrate consumption can be useful.
On the opposite end of bell curve, you have the low or no fat folks. While less of these in the ancestral health community, there are probably more in vegetarian or vegan groups. Among these people, the idea persists that dietary fat is detrimental to health, and by and large is promulgated by nutritional plans from doctors like Dean Ornish. And won can’t forget that the U.S. government has continued to insist that fat is bad, leading to the platforms of organizations like the American Dietetic Association to back their play.
From an overview, diets that are extremely low fat like 80-10-10, commonly used by frugivores, are backed up with arguments that humans closest or direct ancestors are and were primarily herbivores or frugivores, subsisting largely on plants and fruit. This is certainly true, to an extent, though it’s often conveniently ignored that chimpanzees regularly consume meat in the form of other monkeys.
Still, the problem remains that chimpanzees and other high order primates are our closest living relatives. When they eat fruit all the time, it makes a clear argument that perhaps we should eat mostly fruit, and maybe little fat. But the thing is, they are just our closest living relatives.
There are still millions of years of evolution that happened between us since hominids branched off, and the adaptive changes have only sped up since the genus homo started migrating all over the world. It’s hard to say with absolute certainly what our actual closest relatives ate, since they’re now extinct, but one reason to suspect it was similar to the normal omnivorous diet is that they ended up competing with other human ancestors for food, and lost.
As it turns out, the evolution of the colon in primates and hominids might shed an interesting light in how the diets of these various species is significantly different (and why orangutan diets aren’t applicable to humans). On the evolutionary march, the size of the colon and small intestines changed in accordance to the eating patterns of the animals in question. The colon has become progressively smaller by ratio of total intestine and body mass, from orangutan, to chimp, to humans. This correlates well to the observed prevalence of omnivorous behavior, with orangutans and gorillas being almost completely vegetarian, while chimps eat some meat on occasion, and humans eating meat frequently.
This bears credence because vegetable matter and fiber is primarily digested in the colon, or large intestines. The more vegetable matter that is consumed, the larger the colon would need to be to provide adequate fermentation and nutrient absorption. The fact that humans have substantial small intestines, thus provides excellent evidence that we are not engineered to subsist on plant food. Melissa McEwen provided an excellent talk on this concept at the 2011 Ancestral Health Symposium, it was actually one of my favorites.
Ultimately, it should be recognized, that while we might not all be special precious snowflakes, there is bound to be subtle yet important differences in each of our genetic codes. The special adaptations that allowed various human populations and cultures to live and eat in a certain way, do not necessarily translate over perfectly to those of us outside that group, or separated by time and location. The ethno-geographical distribution of lactose intolerance throughout the world should be a clear indication of that.
For ideal and optimal health concerns, I suspect that the most prudent nutritional course would be one that steers towards the middle of the bell curve. The further you stray towards the edges, the more likely that you will encounter detrimental or less-optimal effects towards your health or performance. There may be valid reasons to go either route down the extremes (diabetes, morals, etc.) but it would be advisable to evaluate these changes from the perspective that they are not necessarily ideal, and consider the possibility that they aren’t optimal health-wise for everyone.