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

What It Covers

Harvard evolutionary biologist Daniel Lieberman reviews every major diet — carnivore, vegan, keto, Mediterranean, paleo, raw food, Blue Zones — through an evolutionary lens combined with biomedical and epidemiological data. After personally trying each diet while writing his book, Lieberman argues that nutritional tribalism, marketing language like "optimal," and chronic oversimplification prevent people from making genuinely informed dietary decisions.

Key Questions Answered

• •Evolutionary Diet Framework: No single ancestral diet exists for humans to replicate. Analysis of 12 hunter-gatherer groups with high-quality dietary data shows macronutrient ratios vary wildly across populations — some eating almost entirely plants, others heavily animal-based. Humans evolved as the animal kingdom's ultimate omnivores, using cooking and fermentation to extract nutrition from nearly anything available. The paleo diet's core premise — that one ancestral template exists — is factually unsupported by archaeological and anthropological evidence.
• •Plant vs. Animal Outcomes: Large-scale meta-analyses consistently show plant-based diets produce better long-term health outcomes than meat-heavy diets. Red meat contains carnitine, which gut bacteria convert to TMAO, a molecule mechanistically linked to atherosclerosis. All humans carry a gene variant causing inflammatory responses to a glycoprotein called Neu5Gc found exclusively in red meat. Epidemiological data also shows a dose-response relationship between red meat consumption and cancer risk, with each 85g serving associated with roughly a 13% increased risk.
• •Mediterranean Diet Evidence: The Mediterranean diet holds more scientific support than any other studied diet. A Spanish randomized controlled trial — the PREDIMED study — assigned over 7,500 participants to Mediterranean versus standard diets and was halted after five years because benefits were so pronounced that withholding the diet from the control group was deemed unethical. Its advantages come from a combination of whole grains, monounsaturated fats from olive oil, omega-3-rich fish, diverse phytochemicals, and the absence of refined carbohydrates and added sugars.
• •Blue Zones Statistical Problems: Blue Zones marketing claims that specific regional diets produce twice the centenarian rate, but the base rates are so low — roughly six per 10,000 versus three per 10,000 in the US — that the difference is statistically marginal. Oxford demographer Saul Newman found only 18% of Blue Zones residents had verifiable birth certificates, meaning age data is largely self-reported. Loma Linda, California qualifies as a Blue Zone not because of a specific diet but because its Seventh-day Adventist population avoids smoking and prioritizes exercise.
• •Calorie Restriction and Lifespan: Calorie restriction extends lifespan reliably in yeast, fruit flies, and some mouse lines, but evidence in primates and humans remains absent. A 20-year Wisconsin macaque study initially appeared to confirm benefits, but the control group was fed a high-sugar junk diet — not standard monkey chow. When the NIH repeated the experiment with identical base diets and a 30% calorie reduction in one group, no longevity difference emerged. The mechanism — toggling between mTOR growth pathways and AMPK repair pathways — is real, but lifespan claims exceed current evidence.
• •Fat Cell Permanence and Weight Regain: Fat cells never disappear — they only empty or fill. When fat cells grow sufficiently large, they divide, permanently increasing total fat cell count. Emptied fat cells produce less leptin, signaling the brain to increase food intake to restore energy stores. This means becoming obese at any point makes lifelong leanness physiologically harder. Additionally, increased fat cell count causes those cells to absorb circulating glucose more aggressively, creating hypoglycemic signals that drive further eating — a self-reinforcing cycle that begins with initial weight gain.
• •Carbohydrate Quality Over Category: High-carbohydrate diets are not inherently insulin-spiking or fattening. Populations in Kenya and Rwanda derive at least 65% of calories from carbohydrates yet show near-zero rates of obesity. The critical variable is fiber content and processing level, not carbohydrate presence. Whole grains, legumes, and vegetables digest slowly, producing minimal glycemic response. Industrial milling — invented in 19th-century Hungary — strips fiber and germ from grain, transforming a low-glycemic staple into a high-glycemic processed product. Traditional farming diets and modern refined-grain diets are nutritionally distinct categories.