A Tufts anthropologist gives the evolutionary reason why humans, like our chimp cousins, are so attracted to fatty foods
“Fat is the most calorie-dense food there is, so getting fat of any kind is a huge bonus to wild animals,” said Zarin Machanda, associate professor of anthropology at Tufts. Photo: Shutterstock
Associate Professor of Anthropology Zarin Machanda’s class on Food, Nutrition and Culture used to meet right after lunch. She would always have a plate of cookies available and most students helped themselves even if they’d just eaten. This didn’t surprise Machanda.
“It’s not unusual for any species to be attracted to high-fat, high-sugar foods,” said Machanda, who studies behavior among chimpanzees, humans’ closest living relatives. “I’m not judging. I’d grab a cookie, too.”
Chimps in captivity will choose hamburgers over cucumbers any day, while those in the wild seek out calorie-dense foods like nuts, termites, caterpillars, and even monkey brains.
This preference makes complete sense from an evolutionary point of view, Machanda said.
Most wild animals face limited food resources and work hard to meet their caloric requirements. The larger their size, the more time they typically spend finding and then chewing food so they can digest it.
“The fact that we evolved to crave fat doesn’t mean we need to give in to that craving,” said Zarin Machanda. “Saturated fats are not evil, but we need to make measured healthy choices given the lifestyles we have now.” Photo: Alonso Nichols
Wild chimps in Uganda, the focus of Machanda’s research, require 1200 to 1500 calories a day—not too many fewer than humans—and spend six hours a day chewing their food, expending calories in the process. Fats are estimated to constitute about 2.5% of their diet. Gorillas devote about two-thirds of their day to chewing. Humans who don’t face food scarcity and are able to cook their food typically devote only 30 minutes a day to chewing.
Calories not only keep adults alive but also translate into reproductive success and more babies, especially among female mammals.
“Fat is the most calorie-dense food there is, so getting fat of any kind is a huge bonus to wild animals,” said Machanda.
Being bipedal and having big brains are critical advantages for humans. Schools of thought differ on how eating meat and cooking food shaped human evolution, but Machanda said “we could not have grown our brains without a lot of calories.”
Millions of years of selection has made fats preferred foods across species even if resource limitations and high physical demands are absent. The result for humans is an “evolutionary mismatch” that today contributes to medical problems such as cardiovascular disease, diabetes, and osteoarthritis.
Will evolution catch up with the mismatch? Maybe. Eventually.
But the shifts in our lifestyles and dietary requirements are comparatively recent, evolutionarily speaking. Modern medicine and technology make it possible to live with many disorders. Humans may pass on their fat-loving genes before suffering consequences.
“Until we start making dating apps based on genetic profiles, natural selection may be a moot point when it comes to this particular trait,” said Machanda.
So, are we a prisoner of evolution? Can we look to nature to justify our food choices today? Machanda doesn’t think so.
“The fact that we evolved to crave fat doesn’t mean we need to give in to that craving,” she said. “Saturated fats are not evil, but we need to make measured healthy choices given the lifestyles we have now.”
Sometimes, that means convincing ourselves not to eat that cookie.
