The good news is that I'm not a diet Puritan and I'm hear to tell you that it probably doesn't matter as much what you eat compared to the more important how much you eat. It is really difficult to judge any sort of "best" diet for modern humans to eat, because there is such wide range in the diets of modern humans. For instance, in the Inuit peoples of the arctic, the diet relies almost exclusively on the fat and proteins of marine mammals (Ho et al., 1972), but on the other end of the spectrum, the Aboriginal peoples of Australia thrive on a diet limited to a number of wild plant species with almost no meat at all (Gould, 1980). Thus, there is clearly a wide variety in what can be functional in the human diet.
However, there are a few dietary tenets, based on evidence from nutritional anthropology, that I think are important to adhere to, such as:
- decreasing the consumption of highly refined and processed foods
- increased consumption of "wild" fruits and vegetables
- preference for wild game or grass-fed game over grain fed cattle.
With all of the technological and social innovation in how human beings produce, manage, and process food, there is growing and legitimate concern that these advancements have happened too quickly for human digestive physiology to adapt to them (Trowell & Burkitt, 1981). Which has led many people to support a diet akin to ancestral hunter-gather populations in order to avoid "diseases of affluence" that effect many first world nations (such as obesity, diabetes, coronary diseases, etc.). The problem is that these "Paleo-diets" are really based on conjecture about what hunter-gather populations ate and do not consider the variation in diets of early peoples or the true course of evolution for our digestive physiology. Thus, although I support the general idea of the Paleo-diet, I think most supporters of it have many of the details very wrong.
What do we know about the diet of early humans?
First of all, fossil evidence suggests that modern humans appear about 2.4 mya, but only developed agriculture in the last 12-14 thousand years. This does mean (as proponents of the Paleo-diet assert) that for most of out time on earth, modern humans subsisted using hunter-gather practices; using only wild types of plants and animals as food sources. The problem with diets that attempt to recreate this ancestral hunter-gatherer diet is the assumption that our digestive physiology became adapted to these practices leading to some "optimal" diet for all modern humans based on macro- and micro-nutrient in take of our ancestors.
This assumption is a problem for two reasons. First of all, hunter-gather diets were not at all uniform (based on evidence from contemporary hunter-gatherer populations and reconstructions of ancestral diets from fossil evidence; Ungar & Teaford, 2002). Second, and perhaps most importantly, there is little evidence to suggest human digestive physiology or nutritional requirements changed substantially during that period of our evolution (Milton & Demment, 1988; Milton, 1999). This can be seen in the fact that there are very few differences in the digestive physiology and nutritional requirements of human beings and other great apes.
In fact, those differences that do exist appear to have developed more in the last 12 thousand years post agriculture! For instance, human lactase synthesis in adulthood is a very recent evolutionary adaptation that has reached only a few populations of modern humans in response to the domestication of milk producing animals. To drastically summarize this evolutionary data, it appears that relatively few adaptations have occurred in the human diet in the last 2 million years, most of the adaptations that have occurred are largely regulatory, do not change human nutritional requirements, and are the result of adaptations to the advent of agriculture.
Hmmm... 2.4 million years is a pretty long time, and certainly enough time for evolutionary adaptations to occur, so why didn't they? It might be a question of scale... our 2.4 million years as modern humans pales in comparison to the evolutionary time we spent as protohumans. It is in this time period that our digestive physiology and nutritional requirements were really established. The evidence for this is again comparative studies of nutrition between humans and the other great apes. Both comparative and experimental data show that striking similarities in anatomy and digestive kinetics (e.g., how food moves through your gut) between humans, chimps, orangs, and gorillas (Milton, 1987; Milton and Demment, 1988, Caton, 1997). So in this way I believe supporters of ancestral diets are correct, if modern humans deviate too much from ancestral ways, further compounded by radical changes in lifestyle and physical activity, problems will arise in the form of diseases of affluence.
I would strongly recommend a greater reliance on wild foods as a basis for healthy diets. Wild fruits and vegetables contain greater nutritional density and greater interspecies variation in nutrients than their cultivated counter parts (Conklin-Brittain & Wrangham, 2000; Oftedal et al., 1991). There are similar advantages in consuming wild game to grain-fed cattle (O'Dea, 1992), and the dietary need for animal based proteins is less than you might think (Carpenter, 1994). Although, much to the chagrin of vegetarians and vegans everywhere, the consumption and especially the cooking of meat played an important role in the evolution of the human brain.
To conclude, information on the diets and health of recent and contemporary traditional peoples shows a wide range of highly successful human diets. From hunter-gathers to small-scale agriculturalists who also eat wild foods, we can see all such societies are free of the so-called diseases of affluence whether the diet is made up primarily of proteins and fatty acids acquired from animal source, based on wild plant foods, or even a single cultivated starchy carbohydrate supplemented with wild foods (Lee, 1968; Ho et al., 1972, Neel, 1977; Woolfe & Poats, 1987). Therefore, I would argue, there is not some best human diet, only best human diets.
By that I mean there is not some ideal Paleolithic diet or marco/micronutrient profile, but we should look instead to the shared features of the diets (and lifestyles) of many different traditional societies that spell the difference between their health and ours (Milton, 2000).
I would argue that recent technology has allowed us to circumvent natural barriers in our digestive physiology. Processing, condensing, refining, and otherwise altering both plant and animal foods have allowed us to ingest more energy per day than was otherwise possible with less industrialized food sources. And of course, on the other side of this coin, most of us lead sedentary lives in comparison with more traditional peoples who typically carry out physical activities (often stenuous) for eight hours or more per day; placing a premium on energy expenditure to balance out our energy intake.