You’ve probably heard of the paleo diet – it’s the latest food trend that promises to improve health, aid in weight loss and make life more wonderful in every way.
Is there anything more subject to fashion than diets?
A recent analysis of the paleo diet in the Washington Post helped readers understand the popularity of eating like a caveman. Promoters of the paleo diet, it said, find fault with modern diets because they rely too much on processed food.
The Paleolithic Era extended from about 2.6 million to 12,000 years ago – or from the earliest known use of stone tools through most of human technological prehistory. Our Paleolithic forebears ate what we might call raw materials – meat from grass-fed animals, fish, fruit, vegetables, eggs, tree nuts. The paleo diet forbids grains, cereals, legumes (such as beans and peanuts), potatoes, salt, dairy products, processed foods and refined sugars – anything people ate after the advent of agriculture.
The Post interviewed author Loren Cordain, who wrote “The Paleo Diet: Lose Weight and Get Healthy by Eating the Foods You Were Designed to Eat.” The human body, it says, does best with the nutrition available before people started farming and raising livestock.
Cordain, a Ph.D. who taught in the Department of Health and Exercise Science at Colorado State University, believes that we should eat like our paleo ancestors because our genes haven’t changed that much in the 300 or so generations since they flourished. We’re supposed to hunt, fish and gather from the natural environment because our bodies haven’t evolved to run on the fuel found in grocery stores.
As you might imagine, other experts disagree. The Post talked to Daniel Lieberman, professor of human evolutionary biology at Harvard University and author of “The Story of the Human Body: Evolution, Health, and Disease.” He said that evolutionary adaptations don’t reflect health as much as they do reproductive fitness: “Natural selection really only cares about one thing, and that’s reproductive success.”
If the paleo people were healthier than we are, why didn’t they live longer and produce more offspring? The Post interviewed anthropologist Kenneth Sayers, who pointed out that hunter-gatherers didn’t live much beyond reproductive age. Hard to argue with his analysis: “[I]t’s hard to be healthy when you’re dead.”
Like most food trends, the paleo diet isn’t all about health or science, it’s mostly about nostalgia and the sense that the more “natural” diet of the past, whether it’s 150 years ago or 2 million, is somehow superior.
Evolution isn’t a process toward perfection, it’s a process of adaptation, of trade-offs and compromise. Walking upright, for example, enhances mobility but makes it harder to give birth and predisposes people toward back pain.
As Marlene Zuk, an evolutionary biologist, said, “It’s not like bipedal humans should have said, ‘Wait, wait! Stay in the trees!'”
Lieberman said that the paleo diet makes unscientific assumptions about what our ancestors ate. There wasn’t a single paleo diet, but many. Stone Age people lived in diverse habitats, from the tropics to the tundra, and just like you can’t shop at Trader Joe’s in Alaska, the paleos couldn’t get reindeer in the rainforest.
“There is no one time and place and habitat to which we’re adapted,” Lieberman said.
We have adapted to living in a wide range of habitats, so it follows that we would eat a wide range of foods. We’ve also “adapted” to a less active lifestyle than our hunter-gatherer ancestors. To recommend a modern diet based on what we believe paleolithic humans ate ignores the role of activity in metabolism and digestion.
Still, like many trendy diets, aspects of the paleo diet aren’t without a health benefit. Less sugar and, especially if you’re not very active, fewer calories are good ideas. But unless you have difficulty digesting milk sugar (lactose intolerance), rejecting dairy products isn’t usually a matter of health, but preference. The ability to metabolize milk evolved a long time ago, so paleo diet claims that humans aren’t meant to eat dairy products is just wrong. Dairy products consumed in moderation can be a valuable part of a nutritious diet.
And it isn’t true that the paleolithics didn’t eat grain. Hunter-gatherers in the Middle East ate wild barley, and used mortars and pestles to grind it into flour.
So if you like the paleo diet, enjoy. But remember, it’s not necessarily superior in terms of health benefit to other well-balanced diets. It’s just trendier.