The greater availability of cheap, high-calorie, high-fat foods is contributing to high rates of obesity, he says, but so is the fact that we aren't moving anymore. "If you add even an extra 30 minutes to an hour of moderate exercise a day, it's going to get you to a point where it will make a difference in your long-term energy balance," he says. "Slow and steady is the mantra. You didn't see people in farming and herding societies sprinting around. They moved at a low to moderate level of intensity over the course of an entire day."
On its merits. History aside, the paleo diet has health merit. Except for the dairy and grain issues, it's pretty close to the tenets of the traditional eating patterns like the Mediterranean and Asian diets and other dietary patterns that focus on plants, fish, lean protein, "good" fats, and whole grains. (Cordain says Stone Age eating is closest to a Japanese-style diet.) It also fits into the small but growing movement turning away from factory-farmed meat and toward eating animals fed what they've evolved to eat, like grass rather than grain.
Walter Willett, chair of the department of nutrition at the Harvard School of Public Health, agrees with Cordain that dairy is by no means necessary; most of the world's population survives without it. But he doesn't believe in an all-out grain prohibition. Distinguishing between whole grains and refined grains is more important, he says. "Whole grains do convey a lot of nutrition" and "can be part of a high-quality diet," he says. Refined grains, which have had their nutrients stripped away and have been converted into fine, rapidly absorbable particles, are not. And of course, food choices should be made in the context of an appropriate caloric budget; you can get fat by eating too much of anything.
But the general gist of eating like a caveman—namely, focusing on foods in their whole, natural state, is not going to get much argument. "It comes down to the advice your mother gave you," says Leonard. "Eat a balanced diet and a diversity of foods."
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