What did humans actually evolve to eat? With paleo, keto, vegan, Mediterranean, and a thousand other diets all claiming to be "the one," it's no wonder people feel whiplashed every time they walk into a grocery store. But what if the answer isn't found in the latest diet book, but in millions of years of human evolution?

Join Holly and Jim as they welcome back Harvard evolutionary biologist Dan Lieberman for a second appearance on the show. This time, Dan isn't talking exercise. He's talking food. Drawing on his new book, "Fed Up: What Evolution Reveals About Food, Diet, Health, and Eating Well," Dan explains why there's no single "evolutionary diet," why our supermarkets are a completely unprecedented environment for the human brain, and why willpower alone was never going to be enough. And because Dan doesn't just study diets, he lives them. He shares the surprisingly rough personal experiments he and his wife put themselves through in the name of research.

By the end of this episode, you'll understand exactly why eating well feels so hard in the modern world, and why that struggle has nothing to do with a lack of discipline.

Discussed on the episode:

• Why an evolutionary biologist says there's no such thing as "the" diet humans evolved to eat
• The "naturalistic fallacy" and why what our ancestors did isn't automatically what we should do
• What happened when Dan and his wife tried a raw food diet for several days (and why it ended with a bagel)
• The one natural food that's high in both sugar and fat, and what it reveals about why we crave certain foods
• How food processing quietly changed what's actually in your food, long before you ever open the package
• Why Dan calls modern ultra-processed foods "hyper-matched" to our brains
• The real reason low-carb and low-fat diets can both work, and why neither is right for everyone
• What Dan learned trying the Atkins diet as a self-described "carboholic"
• Why the Mediterranean diet keeps coming out on top, and whether that's fair to other traditional diets around the world
• His take on the vegan vs. carnivore debate, and why he wouldn't attempt one of them
• A listener's question about why the same diet can work great for one person and fail for their sibling
• Practical advice for eating well on a tight grocery budget
• The one thing Dan wants every listener to remember about their own struggles with food.

Resources mentioned:

• Dan Lieberman's book: "Fed Up: What Evolution Reveals About Food, Diet, Health, and Eating Well"