Harvard Professor: “I Tried Every Diet. This Is By Far The Worst.” - Daniel Lieberman - #1137

You spent years researching major diets and trying them. Before the nutritional religions—vegan, carnivore, keto—what did that do to your own beliefs about food?

It was fun. I was writing about diet’s evolution, and my wife and I lived through some diets rather than only reading the literature. The science can be bewildering: top journals publish opposing claims about saturated fat, salt, you name it. I wanted evolutionary, biomedical, cultural, anthropological, and lived evidence in one picture.

What does evolution add? And why does food make people so tribal—almost theological?

Evolution lets us ask why. We emerged through evolution, and diet is no exception. People once ate according to local culture; now global foods are everywhere, and what we eat—or refuse to eat—can become identity. Dietary effects can take decades, so every choice involves some faith. We want certainty long before we can know whether it paid off.

Is plant-based eating better than carnivore eating? And why has carnivore become such a force?

Nearly every diet has a grain of truth. Meat is nutritious and mattered in our history. But broad long-term evidence generally favors diets richer in plants—not sugar and refined starch called healthy because they came from plants. More meat is associated with higher cancer risk in several studies, with plausible gut and inflammation mechanisms. Carnivore can feel miraculous when someone moves from soda and fast food to structure. Better than a terrible diet does not prove it’s best.

Protein is the new hot girl at school. Do we need to chase a gram per pound of body weight?

Protein is essential, filling, and active people, pregnant people, menstruating people, and older adults may need more. But the body doesn’t warehouse extra protein as muscle; enormous intakes have no magical payoff. Dose depends on age, activity, muscle status, and goals. And protein is not synonymous with meat: beans, legumes, whole grains, soy, nuts, and grain-legume pairings have fed farming societies worldwide.

Why does the Mediterranean pattern keep coming up? Is it the plants, less meat, or simply easier research?

Eating one thing displaces another, which makes nutrition hard. Epidemiology is confounded: active people often eat better, and vegetarians may smoke less. We can’t assign twins to opposite diets for fifty years, but we shouldn’t discard the evidence. Be foxes, not hedgehogs: use mechanisms, population studies, trials, and randomized studies together. Mediterranean-style diets have unusually strong support: whole grains, legumes, vegetables, fruit, olive oil, fish, diversity, and less added sugar, refined carbs, saturated fat, and red meat.

What about Blue Zones and Paleo—can a particular menu get us to one hundred, or recreate an ancestral diet?

Blue Zones advice is often Mediterranean-like and sensible, but centenarian marketing gets silly. Reaching one hundred is rare, records can be questionable, and Loma Linda Adventists also tend not to smoke, exercise, and care for themselves. I hate “optimal diet”: optimal for whom, at what age, with what genetics and risks? Paleo is right about limiting sugar and junk, but hunter-gatherers ate huge variety—plants, animals, often legumes and grains. We are extraordinary omnivores.

You tried raw food. How did that go?

By far the worst. Cooking makes nutrients and energy more available; I ate constantly and stayed hungry. My wife lasted three days, came back happy with a bagel, and I lasted four. Cooking is ancient and fundamental: it improves digestion, makes food safer, and helped support our big brains. Raw beans can hurt you, but cooking and fermentation reduce lectins and phytates. Cooked spinach and beans are healthy foods, not hazards.

If traditional diets could be healthy, why is obesity such a huge global problem?

Traditional farming food is not a modern white-bread diet. Whole-grain sourdough with lentils is very different from refined flour and added sugar. Our environment is full of highly processed food engineered around sugar, fat, salt, texture, temperature, and flavor variety. A Big Mac hits nearly every sensory button; Doritos are formulated to keep you reaching back in. Activity matters enormously too, including for insulin sensitivity.

People want one clean answer: keto, fasting, calorie restriction, GLP-one. Is there one?

Low-carb can produce somewhat greater weight loss under ideal conditions, but it’s hard to sustain; as a runner, I hated Atkins cravings. High-carb can work when carbs are fiber-rich and minimally refined—communities I work with in Kenya and Rwanda eat lots without widespread obesity. Fasting may support alternation between growth and repair, but proof it extends human life is lacking. GLP-ones can be life-changing, but muscle loss, quitting, appetite rebound, and fat-heavy regain are real. Strength train if you use them.

What are the durable guardrails—and is this personal agency, system change, or both?

Avoid heavily refined, ultra-processed foods where you can: added sugar, fat, white flour, and mysterious additives. If I see maltodextrin, I walk away. Juice, fruit roll-ups, and mountains of dried fruit are not whole fruit. But stressed people cannot shop perfectly against companies targeting appetites built for survival. We need education, clear front labels, healthier convenient foods, and a real conversation about junk-food policy. Our ancestors learned to find food. We have to learn to choose it.

That’s the useful unsexy answer: no magic diet or perfect menu—just better evidence, better food environments, and fewer people selling certainty. Your book is Fed Up, built so people can check the data.

That was the hope. It’s readable and fun, but has the references too. I’d rather people understand the trade-offs than hand their judgment to the latest dietary salesman.