Should we look backward for clues to the perfect human diet? And not just back a few generations—to a world before french fries were a major source of vegetables and the Super Big Gulp encouraged the downing of 64 ounces of soda in one sitting—but waaaaaay back? Some people think so, arguing that we ought to turn to a "caveman diet" or "paleo diet" based on what they think early humans and human ancestors ate for millions of years, from the Paleolithic era until the agricultural revolution began about 10,000 years ago. "Seventy percent of our calories come from foods these folks never would have consumed," says Loren Cordain, an exercise scientist at Colorado State University in Fort Collins and author of The Paleo Diet.
There's certainly broad agreement that in the past few generations we have strayed far from an eating pattern that supports maximum health. Whatever our ancestors ate, it sure wasn't the current Western diet, which is heavy on saturated fat, salt, and processed foods based heavily on soybeans and on corn. That style of eating has been associated with a variety of health problems and is, by all accounts, a mess.
Cordain suggests we mimic the diet of our hunter-gatherer forebears and eat lean meats (especially grass-fed beef, wild game, and free-range birds rather than farm-raised animals), fish, plants, fruit, and nuts. Milk is not on his list; he says there are no evolutionary roots for it in the hunter-gatherer society, where milking wild animals wasn't possible. And contrary to most nutritional advice, he disdains grains, even whole ones, because he says our bodies aren't well adapted to eating them, especially in mass quantities.
The study of how human diets evolved is a rich field, with researchers approaching the problem from angles including examining dental microwear, the tiny pits and dents in teeth that suggest how they were used, and hypothesizing about how cooking affected our progress. It's also full of pitfalls, because trying to reverse-engineer what exactly early humans and prehumans ate is difficult, and fossils may actually lead us astray. For example, says Peter Ungar, an anthropologist at the University of Arkansas-Fayetteville, conventional wisdom used to hold that because the skull of one ancestral close cousin who lived 2 million years ago, "Nutcracker Man," featured big, flat teeth, he must have used them to feed primarily on nuts, seeds, and other hard sources of nutrition.
Not so, says Ungar. Now researchers believe that jaw and teeth structure can indicate only the capability to eat certain types of food, perhaps in times of shortage or scarcity, not that those foods were their most common or optimal choices. Just look at gorillas, our primate relatives: They have huge molars and chewing muscles for eating leaves and tough foods, yet 11 months of the year they eat softer things, like fruit and bugs, that don't require that kind of masticatory firepower.
So Ungar says it's not at all clear that we should eat foods X, Y, and Z simply because we suspect our ancestors did. "Most people who study the fossils of our human ancestors are very reticent about using what little we know about their diets to show what we should be eating today," he says. Instead, he points to variety as the real key to the evolution of the human diet. "Our success is pegged to the fact that we have been able to survive in so many places," he says. William Leonard, chair of the anthropology department at Northwestern University in Evanston, Ill., agrees. "The hallmark of human nutrition for me is the flexibility and diversity," he says. "It's the ability to make a meal in any environment."
Ungar and Leonard don't blame our modern diet-related health problems on any specific food group. Rather, they're convinced that our major problems these days are the lack of that diversity in our diet—and a positive energy balance. In other words, unlike our Paleolithic forebears, we are taking in more calories than we burn off. "The difference is not simply in what we're eating but in what we're doing," says Leonard.
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."