Fed Up weaves together three stories. First, Lieberman tells the fascinating history of food and diets. What did we evolve to eat, and how did farming and industrialization change our diet? He then describes his own experiences with the major 'big idea' diets that mirror this history. Beginning with raw foodism and the Paleo diet, progressing to the Mediterranean and Blue Zone diets, and then sampling more recent weight-loss diets such as Weight Watchers, Atkins, and Ornish. Finally, he uses an evolutionary anthropological framework to demystify and evaluate the multifaceted science behind these diets and their effects on health. Among the many questions Lieberman addresses are: What is in food, how do we digest it, and what are we adapted to eat? Why do we cook? How does food affect aging and how we get sick? Why is it so easy to gain weight but so hard to lose it?

In addition to introducing readers to the fascinating history of food and the fundamentals of nutrition and digestion, it debunks and disentangles the confusing and divergent prescriptions we hear and read so often. Why are some big idea diets high-fat, others low-fat, and only some restrict calories? Why is no diet highly effective for weight loss? Beyond myth-busting, Fed Up concludes with scientifically sound guidance without being prescriptive or facile. It summarizes what we know and don't know about how people lose weight and prevent weight gain, and which diets make sense in the light of ancient adaptations, recent history, and today's food landscape. Lieberman also touches upon the evolutionary underpinnings behind what diets have been shown to help people age well while decreasing their risk of heart disease, cancer, metabolic syndrome, dementia, and depression.

Food ought to be enjoyed and shared, but for many, choosing what to eat has become confusing and stressful. By telling the story and science of food and diets, Fed Up engagingly empowers readers with the information and concepts they need to make their own choices.