Diversity Of Diets

THE VARIETY OF SUCCESSFUL dietary strategies employed by traditionally living populations provides an important perspective on the ongoing debate about how high-protein, low-carbohydrate regimens such as the Atkins diet compare with those that underscore complex carbohydrates and fat restriction. The fact that both these schemes produce weight loss is not surprising, because both help people shed pounds through the same basic mechanism: limiting major sources of calories. When you create an energy deficit—that is, when you consume fewer calories than you expend—your body begins burning its fat stores and you lose weight.

The larger question about healthy weight-loss or weight-maintenance diets is whether they create eating patterns that are sustainable over time. On this point it appears that diets that severely limit large categories of foods (carbohydrates, for example) are much more difficult to sustain than are moderately restrictive diets. In the case of the Atkins-type regimen, there are also concerns about the potential long-term consequences of eating foods derived largely from feedlot animals, which tend to contain more fat in general and considerably more saturated fats than do their free-ranging counterparts.

In September 2002 the National Academy of Sciences's Institute of Medicine put forth new diet and exercise guidelines that mesh well with the ideas presented in this article. Not only did the institute set broader target ranges for the amounts of carbohydrates, fat and protein that belong in a healthy diet—in essence, acknowledging that there are various ways to meet our nutritional needs—the organization also doubled the recommended amount of moderately intense physical activity to an hour a day. By following these guidelines and balancing what we eat with exercise, we can live more like the Evenki of Siberia and other traditional societies— and more like our hominid ancestors. — W.R.L.

expensive. According to recent estimates, more than half of adult Americans are overweight or obese. Obesity has also appeared in parts of the developing world where it was virtually unknown less than a generation ago. This seeming paradox has emerged as people who grew up malnourished move from rural areas to urban settings where food is more readily available. In some sense, obesity and other common diseases of the modern world are continuations of a tenor that started millions of years ago. We are victims of our own evolutionary success, having developed a calorie-packed diet while minimizing the amount of maintenance energy expended on physical activity.

The magnitude of this imbalance becomes clear when we look at traditionally living human populations. Studies of the Evenki reindeer herders that I have conducted in collaboration with Michael Crawford of the University of Kansas and Ludmila Osipova of the Russian Academy of Sciences in Novosibirsk indicate that the Evenki derive almost half their daily calories from meat, more than 2.5 times the amount consumed by the average American. Yet when we compare Evenki men with their U.S. peers, they are 20 percent leaner and have cholesterol levels that are 30 percent lower.

These differences partly reflect the compositions of the diets. Although the Evenki diet is high in meat, it is relatively low in fat (about 20 percent of their dietary energy comes from fat, compared with 35 percent in the average U.S. diet), because free-ranging animals such as reindeer have less body fat than cattle and other feedlot animals do. The composition of the fat is also different in free-ranging animals, tending to be lower in saturated fats and higher in the polyunsat-urated fatty acids that protect against heart disease. More important, however, the Evenki way of life necessitates a much higher level of energy expenditure.

Thus, it is not just changes in diet that have created many of our pervasive health problems but the interaction of shifting diets and changing lifestyles. Too often modern health problems are portrayed as the result of eating "bad" foods that are departures from the natural human diet—an oversimplification embodied by the current debate over the relative merits of a high-protein, high-fat Atkins-type diet or a low-fat one that emphasizes complex carbohydrates. This is a fundamentally flawed approach to assessing human nutritional needs. Our species was not designed to subsist on a single, optimal diet. What is remarkable about human beings is the extraordinary variety of what we eat. We have been able to thrive in almost every ecosystem on the earth, consuming diets ranging from al-

most all animal foods among populations of the Arctic to primarily tubers and cereal grains among populations in the high Andes. Indeed, the hallmarks of human evolution have been the diversity of strategies that we have developed to create diets that meet our distinctive metabolic requirements and the ever increasing efficiency with which we extract energy and nutrients from the environment. The challenge our modern societies now face is balancing the calories we consume with the calories we burn. S3

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