How Our Evolutionary Past Shapes Our Health Today
by Amanda Rossillo | American Scientist Magazine | February 25, 2022
Featured as one of American Scientist’s top 10 blog posts of 2022
Hadza women digging for tubers. Courtesy of Herman Pontzer.
Americans have been fixated on weight for nearly a century. Unusual diets and vigorous exercise programs have proliferated, making it difficult to untangle the roles that diet, exercise, calories, and metabolism play in contributing to weight. Most experts say that it all comes down to “energy in” versus “energy out.”
On January 25, 2022, Sigma Xi hosted a virtual presentation (see video below) by one such expert: Herman Pontzer, an evolutionary anthropologist at Duke University, who is the author of the 2021 book Burn: New Research Blows the Lid Off How We Really Burn Calories, Lose Weight, and Stay Healthy. In his presentation, Pontzer discusses his research on energy expenditure in traditional societies such as the Hadza, a tribe in Tanzania that obtains food by hunting and gathering, and explains that studies of hunter-gatherers have shed light on how our evolutionary past influences our health today. He also discusses some common myths about metabolism and weight loss.
Pontzer views human metabolism as a foundational “unseen adaptation” of our species. Humans burn far more calories than do other primates of similar body size. This capacity evolved to support not only activities such as hunting and gathering but also traits such as bigger brains and longer lives—characteristics that Pontzer regards as “the center of what makes us human.”
As processed foods and more sedentary lifestyles have become the norm in many industrialized societies, the risk of developing metabolic syndrome (which can lead to heart disease, stroke, and type 2 diabetes) has increased. The first step in getting healthier is to learn to distinguish metabolic fact from fiction.
A Hadza man heads toward a baobab tree in search of honey. The bark of the baobab is highly suitable for beehive construction, and honey is a staple of the Hadza diet. Courtesy of Herman Pontzer.
Metabolic Myth #1: Exercise boosts your metabolism. Pontzer found that the Hadza walk an average of 13,000-19,000 steps per day—far more than the average American. However, he and his colleagues also found that the Hadza and people from other traditional societies burn about the same number of calories per day as do people who live in industrialized societies. “This suggests that daily energy expenditure is constrained,” he says. “Your body adapts to exercise to keep energy expenditure within a narrow range.”
Metabolic Myth #2: Exercise is a great way to lose weight. Because our metabolisms don’t have a lot of wiggle room when it comes to energy expenditure, exercising more without changing your diet won’t result in significant weight loss. “If you burn more calories, you end up eating more to replenish them,” says Pontzer.
Metabolic Myth #3: Exercise isn't working if you don't lose weight. Even though exercise may not boost your metabolism or be much help in losing weight, it is still beneficial to your health. It affects every system in the body in ways we are only beginning to understand. Exercise reduces chronic inflammation, stress reactivity, and levels of reproductive hormones, and Pontzer argues that constraint of energy expenditure helps explain these reductions. In the question and answer period after his talk, he notes that the reduction in hormone levels reduces the risk of developing cancer of the ovary, breast, or prostate.
Metabolic Myth #4: Calories don't matter. Pontzer sums up his response to this myth rather succinctly: “Life is a game of turning energy into kids, and calories are the currency of life.” He maintains that when it comes to losing weight, calories are the only thing that matters. Although we tend to think of weight loss as depending on the perfect combination of exercise and diet, Pontzer says it’s really a function of burning more calories that you consume, regardless of the source of those calories.
Metabolic Myth #5: Humans evolved to eat a meat-heavy Paleo diet. Traditional foraging adaptations are diverse. Although some traditional societies (Arctic communities, for example) do tend to rely on meat, many others (including equatorial ones) do not. Pontzer’s research on diet and foraging strategies among the Hadza shows that meat has provided a relatively small proportion of the calories in their diet. Like the people in many other traditional societies, they consume large amount of carbohydrates, berries, fiber, and honey.
Metabolic Myth #6: A slow metabolism dooms you to obesity. Although some individuals may have a “fast” or “slow” metabolism relative to their size, a slow metabolism does not translate to actual weight gain: “Metabolism doesn’t determine your weight,” Pontzer says, “it responds to it. Your genes have a lot more to say about how much you might struggle with weight.” Nearly all of the hundreds of gene variants associated with obesity are active mostly in the brain, which is where sensations of fullness primarily originate.
Metabolic Myth #7: Obesity is a sign of personal failure. Pontzer concludes his talk by emphasizing that obesity is no one’s fault—rather, it’s a product of the foods we’re surrounded by. Over the past few decades, cheap, energy-dense foods have become much more prevalent. These foods typically lack protein and fiber, which are important nutrients that signal to the body that it’s full. Because of this, people tend to overconsume these foods. “It’s not a personal failure issue, it’s the way we’ve built our food environments,” he says. “We need to address that as a society if we want to avoid metabolic disease and obesity.”
Understanding the relationships between and functions of diet, exercise, calories, and metabolism isn’t easy, but doing so is a crucial first step in regaining control of our health both as individuals and as a society. And Pontzer’s findings about life among the Hadza suggest that spending more time outside with loved ones would probably help too.
Visit www.hadzafund.org to learn more about Hadza culture and to support ongoing healthcare and research initiatives that protect their traditional way of life. For more on Pontzer’s insights about diet and metabolism, consult Burn.