September 29, 2026 In his new 2026 book, Fed Up: What Evolution Reveals about Food, Diet, Health, and Eating Well, Daniel E. Lieberman explains the mismatch between what humans evolved eating over hundreds of thousands of years and the diverse diets eaten today, explaining how ancient survival instincts may be maladaptive for today’s industrialized food. An anthropologist, Lieberman studied indigenous and subsistence populations in Africa, Latin America, and the Arctic and shows that people can remain healthy on very different macronutrient mixes, especially when diets are less processed and activity levels are high.
Humans evolved powerful defenses against calorie shortage, hunger, preferences for energy-dense food, fat storage, and metabolic adaptations, but evolution had much less reason to protect humans against a permanent abundance of cheap calories. That produces the familiar modern paradox of undernutrition and obesity coexisting in populations. Humans evolved to store fat and defend body weight, so losing weight is not just a matter of weak willpower. Biology pushes back through hunger, reduced energy expenditure, and rebound effects.
Lieberman observes that evolution does not point to one perfect human diet; instead, it shows that humans are dietary generalists, that modern ultra-processed food environments exploit our evolved vulnerabilities, and that to eat well can be flexible, rather than to buy into a single dietary ideology. He debunks the fad diets that try to reduce healthy eating to one big idea, such as Paleo, low-fat, low-carb, vegan, carnivore, fasting, which are too usually too simplistic.
Many farming societies have historically obtained most of their calories from grains, tubers, legumes, vegetables, and other plant foods, with meat eaten intermittently or in relatively small quantities. Lieberman treats such diets as perfectly compatible with human biology. Humans do not need a high-meat diet. Large populations have lived successfully for generations on diets in which meat is a relatively small component. Moreover, eliminating plant foods from one’s diet can create deficiencies in key nutrients. “Unlike hunter-gatherers, farmers are susceptible to diseases such as scurvy (from insufficient vitamin C), pellagra (from insufficient vitamin B3), beriberi (from insufficient vitamin B1), goiter (from insufficient iodine), and anemia (from insufficient iron). Relying heavily on a few crops or sometimes just one crops” sacrifices quality and diversity for quantity.”
Humans evolved to eat a very wide range of foods, not one ancestral ideal diet. However, modern highly engineered foods are consistently more harmful than ordinary whole or traditional foods, because they exploit evolved appetites for sugar, fat, salt, and easy calories in ways our bodies and brains are poorly equipped to regulate.
“The invention of agriculture caused the human food supply to increase in quantity and deteriorate in quality, but food industrialization multiplied this effect.”
The book also examines glucose and insulin regulation, fat storage, appetite, cortisol and stress, muscle loss and aging, and how drugs such as GLP-1 agonists affect appetite and body composition. This evidence is used to explain why some diets can work mechanistically, but also why real-world adherence is so hard and why weight regain is common. “An evolutionary perspective predicts that most diets and fitness programs will fail, as they do, because we still don’t know how to counter once-adaptive primal instincts to eat donuts and take the elevator.”
Lieberman laments: “We didn’t evolve to be healthy, but instead we were selected to have as many offspring as possible under diverse, challenging conditions. As a consequence, we never evolved to make rational choices about what to eat or how to exercise in conditions of abundance and comfort.”
– edited by Steven Hansch of World Hunger Education Service
