Is a varied diet over-rated?

I attended a very interesting session this morning at the 5th Nutrition and Health Conference that I'm attending here in Phoenix, AZ. Dr. Daphne Miller, a professor of medicine at University of California at San Francisco, gave a presentation on her new book, The Jungle Effect.

Over the past ten years, scientists have spent a lot of energy investigating the world's healthiest and longest-lived populations, trying to figure out what they are doing right. Why do they live so much longer and have vastly lower rates of cancer, heart disease, diabetes, and other diseases than Western countries?  We've picked apart and analyzed the traditional diets and lifestyles of Okinawans, Cretans, Icelanders, Cameroons, Pima Indians, and so forth, in an attempt to codify, once and for all, the healthiest diet.

The problem, as Dr. Miller discovered when she travelled to all of these places to see for herself, is that health and longevity are about the only things that these cultures have in common.  The robust Tarahumara Indians, for example, eat a diet of 80% carbohydrates (mostly in the form of starchy vegetables like corn and potatoes!), while the indestructable Cretans get almost 50% of their calories from fat.  Some long-lived cultures eat almost no meat, while the hale and hearty Icelanders eschew vegetables as "animal feed" and eat large quantities of lamb and fish. 

I can't do justice to Dr. Miller's entire argument in this short post (although I highly recommend checking out her new book), but she concludes that traditional diets work chiefly because they are based on the plants and animals that flourish in the local ecosystem, prepared and consumed in a way that has been fine-tuned by generations of trial and error to provide optimal nutrition for those people.

That's not to say that only indigenous people will flourish on a particular traditional diet, says Dr. Miller. If you adopt ANY of these diets, she says, you will likely see an improvement in your health. Conversely, all of these incredibly healthy populations suffer from the "migration effect." When they migrate to Western industrialized nations (or McDonalds inevitably sets up shop in their small village), within a few years, they invariably begin to show the same sorts of degenerative conditions that are routine in Westerners.

Despite the staggering differences between various, apparently "successful" indigenous diets, Dr. Miller has attempted to find the common threads. Among the key concepts she identifies: consumption of native grains, fermented foods, spices, and communal (unhurried) eating. But the differences still seem to loom larger than the commonalities.

A unifying concept that Dr. Miller didn't mention is that all indigenous diets are composed of a relatively small list of foods. In most cases, about two dozen foods provide 95% of the calories--in some cases,  fewer than a dozen! Compare this with the tens of thousands of food products we are confronted with at the grocery store. Hundreds of kinds of produce from every climate inn the world. Dozens of kinds of grains.  Scores of protein sources.  We think nothing of eating Indian food on Monday, Chinese on Tuesday, sushi on Wednesday, Latin-American on Thursday and Greek on Friday. And this got me thinking: Is a varied diet over-rated?

As a nutritionist, I myself frequently cite the advantages of a varied diet. First and foremost, you increase the range of nutrients you consume by eating a wide variety of foods, especially whole foods.  Secondarily, you limit your exposure to toxins (natural or unnatural) that might be present in certain foods.  It's a cover-all-your-bases and hedge-your-bets sort of approach and one that always made sense to me.

On the other hand, some of these indigenous cultures remain in enviably good health on a diet of two or three vegetables, one source of protein and one or two kinds of grain.  It makes you think, doesn't it? For one thing, it is a fact that we tend to eat more when confronted with a large variety of foods than we do when we eat just one or two things at a meal. (Think of your behavior at buffets.)

I'm hoping to have a chance to catch Dr. Miller later in the conference to get her take on this (and I've got to run to the next session now), but in the meantime, what do you think?  Could we improve our diets just by making them simpler?

If you had to choose just two dozen foods to make up your entire diet for a week, what would they be?