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

[restricted term] and Carb Quality Affect Metabolism More Than Quantity

Glucose in the blood is tightly regulated by the body, with only about a teaspoon and a half circulating at any time. If this range is exceeded, serious health consequences such as hyperglycemia can occur. The body responds to increased blood glucose from a meal by releasing [restricted term], the hormone responsible for lowering glucose by facilitating its uptake into cells and promoting storage.

However, the metabolic impact of carbohydrates depends largely on their quality rather than their quantity. Refined carbohydrates and foods high in added sugars cause rapid spikes in [restricted term] and consequently promote greater fat storage. Conversely, unrefined carbohydrates—such as those found in whole grains, legumes, and vegetables—are rich in fiber, slowing glucose digestion and minimizing both blood sugar and [restricted term] surges.

Traditional farming diets across the Mediterranean, Asia, and Africa, for instance, commonly relied on bread made from whole grains, legumes like lentils and chickpeas, and minimal refined ingredients. These diets, rich in fiber and low in processed sugar, do not significantly raise [restricted term] and were historically not associated with obesity. Lieberman notes that modern perceptions have been distorted by the introduction of refined flours in the industrial era, which greatly alter the metabolic response and health consequences of cereal-based diets.

Observational evidence from regions like Rwanda and Kenya, where individuals typically derive at least 65% of their calories from high-fiber carbohydrates, supports this distinction. Despite high carbohydrate intake, obesity and overweight are rare due to the predominance of fiber-rich, minimally processed plant foods and high levels of physical activity.

Physical activity also improves muscle [restricted term] sensitivity, reducing the need for [restricted term] to process carbohydrates. This means active individuals experience a metabolic advantage beyond mere calorie burning, further highlighting the importance of lifestyle factors in addition to diet composition.

Protein Is Essential; Excess Offers No Benefits

Protein is a critical macronutrient, as the body cannot synthesize all necessary amino acids. These essential amino acids must come from the diet, making protein indispensable for health, muscle maintenance, and bodily functions across all ages, especially for those who are physically active, pregnant, menstruating, or aging.

Lieberman stresses that although protein is necessary, the body cannot store excess amounts. Any protein beyond what the body needs is converted to fat. Popular high-protein guidelines such as one gram per pound of body weight may be unnecessary for most people; there is no simple dosage that suits everyone due to differences in age, activity, and health status. Excessive protein offers no additional benefit and, at extreme levels, can even cause harm like kidney damage.

Plant-based proteins are both complete and adequate when paired thoughtfully. Many cultures have relied on combinations such as rice and beans or corn and legumes to ensure complementary amino acids. Soy is a complete plant protein, and foods like quinoa, legumes, nuts, and whole grains provide ample protein without the need for animal sources, disproving the notion that only meat delivers high-quality protein.

Food Processing Boosts Caloric Availability and Energy Extraction

The processing of food—especially through cooking and mechanical breakdown—substantially increases calorie extraction and digestibility. Cooked food releases more nutrients than raw food because cooking breaks down cell walls and tough fibers. Lieberman describes personal experience on a raw food diet, noting persistent hunger due to low energy absorption. Experiments with animals (such as grinding up rats for boa constrictors) show that processing yields greater caloric return and less undigested waste.

Mechanically processed foods—like smoothies or peanut butter—offer more calories than the same foods consumed whole. For example, ground peanuts (in peanut butter) provide about 25% more energy than whole peanuts due to increased surface area for digestive enzymes. Similarly, blending a banana increases energy availability compared to eating it whole.

Highly processed foods often include che ...

Dietary choices have evolved into deeply personal identities in modern society, often defined by strong beliefs and group affiliations. Daniel Lieberman and Chris Williamson explore the psychological and cultural forces behind why dietary dogmas are so persistent and divisive.

Diet as Identity and Meaning In Eroding Cultural Institutions

Modern Abundance Enables Self-Identity Through Diet Choices

Daniel Lieberman explains that diet has long been a way for people to define themselves, often by what they don’t eat. Traditionally, religious and cultural dietary rules—whether kosher, Jain, or others—helped shape group identity. In the modern world, as established sources of meaning erode, food choices have taken on greater significance. Lieberman observes that today, people search for meaning and identity in what they eat.

Dietary Movements Resemble Cults, Fostering Groupthink and Rule Adherence

Lieberman describes some diet movements as “nutritional theology,” likening them to online cults. Groupthink becomes common, with adherents fiercely agreeing on the “right” diet and policing adherence to communal rules. Williamson echoes this sentiment, highlighting the cult-like nature of online dietary communities.

Dietary Disagreements Threaten Health Because They Imply Alternative Diets Suggest one’s Choices Might Lead To Early Death or Decline

Williamson points out that disagreements about diet go deeper than abstract debate. Since people believe diet is tied directly to longevity, an alternative dietary philosophy threatens personal security. If someone else is right, it implies your diet may be wrong—with real-world implications for your health and mortality. As a result, divergence in dietary opinions can feel like an existential threat, intensifying the emotional stakes of these disagreements.

Belief-Based Dietary Choices Stem From Decades-Long Health Outcome Observation

Dieters Must Have Faith in Benefits Before Experiencing Longevity Effects, Requiring Leap-Of-faith Decisions

Lieberman elaborates that it can take decades for the health effects of diets to manifest. This lag forces people to take a leap of faith with any dietary plan. Even if the Mediterranean diet is well-studied, for example, no one can personally know if it “works” for them until perhaps 30, 40, or 50 years have passed. As a result, dietary decisions inevitably rest on trust, faith, or belief, supported by friends, science, community, or personal values.

Observation Period Shows Belief Frameworks Hinder Rational Conversion Between Dietary Camps

Because outcomes are slow and often uncertain, people rely on belief frameworks rather than direct evidence—making it difficult to switch camps or update beliefs rationally. Each group uses its own logic and communal experience to validate its dietary choices.

Any Diet Success Creates Confirmation Bias When Switching From Processed Foods

Any initial health improvement—often a result of simply switching away from processed foods—can generate strong confirmation bias. Dieters interpret early positive changes as proof of their chosen approach’s effectiveness, reinforcing group identity and making it harder to critically assess or change dietary beliefs.

Rules and Simplicity Comfort Food Choices

Humans Face the Novel Dilemma Of "What Should I Eat," Causing Decision ...

Ultra-Processed Foods Overwhelm Satiety By Activating Sensory and Neural Pathways

Engineered foods are specifically designed to exploit and overpower our natural mechanisms for feeling full. Daniel Lieberman points out that most natural foods do not combine high levels of both sugar and fat. The main exception is milk, which is the first food humans consume and is rich in both. After weaning, however, such combinations are rare in natural environments—unless accessed through supermarkets or food manufacturing. Today’s favorite engineered foods—such as fast food items—balance sugar and fat in quantities that, on their own, would be overwhelming or unpleasant, but together make products hyper-palatable. Adding salt to these blends further intensifies the brain’s reward response.

Modern processed foods are crafted to heighten nearly every taste sensation and texture: hot and cold, crunchy and smooth, sweet and salty, and complex, engineered flavors. Lieberman cites the example of a McDonald's Big Mac, which delivers almost every dimension of flavor and texture except spicy, all in one item. Products like Doritos boast up to 30 ingredients, carefully balanced so no single flavor stands out too harshly, continually activating pleasure and reward centers in the brain.

Even seemingly trivial features like color variation are engineered to increase consumption. Lieberman describes how M&Ms, which are identical in taste regardless of color, prompt novelty-seeking behavior: eat a red one, then a green one, then a brown one, with the illusion of variety encouraging more consumption. This is deliberate design by food companies to engineer consumption patterns and maximize intake.

Obesity Epidemic Mainly Driven by Dietary Changes, Not Reduced Physical Activity

Lieberman emphasizes that the obesity epidemic in the U.S. is due primarily to changes in the food environment rather than a global drop in physical activity. While exercise does play a role in metabolic health and [restricted term] sensitivity, the vast majority of weight gain can be traced to increased caloric intake as a result of hyperpalatable, calorie-dense foods now prevalent everywhere. More than 50% of supermarket products are ultra-processed, designed to be highly appealing, affordable, convenient, and addictive, making natural and healthy food choices increasingly challenging.

Statistics illustrate the impact: 40% of American adults are classified as obese, 35% as overweight, leaving just 25% at a normal BMI—even as BMI itself is not a perfect measure. Among teenagers, 25–30% are now classified as obese, suggesting lifelong struggles with weight for a significant portion of the next generation.

Products marketed as healthy alternatives, such as meal replacements like Soylent or certain ultra-processed vegetarian foods, are not immune. These often contain emulsifiers, solvents, or other unknown additives whose long-term effects are not well studied. Vigilance and informed decision-making are now necessary to avoid ultra-processed foods and their health consequences.

Fat Cell Dynamics and Hormonal Signaling Hinder Weight Loss More With Prior Weight Gain

Obesity leads to increases in both the number and size of fat cells, and these biological changes become barriers to future weight loss. Fat cells release leptin, a hormone that communicates energy stores to the brain. When fat is lost, leptin levels drop, signaling hunger and an increased appetite—a defense mechanism to restore previous fat levels. This hormonal feedback creates a new, higher "defendable" body set point, making sustained weight loss increasingly difficult for those who have gained significant weight.

Long-term weight loss maintainers demonstrate consistent strategies to work against these b ...

Daniel Lieberman provides a comprehensive view of how human dietary evolution is closely intertwined with natural selection, physiological tradeoffs, varied ancestral diets, and the transformative impact of cooking.

Natural Selection Optimized Humans For Reproduction, Creating Modern Mismatches

Evolution Shaped Dietary Preferences and Metabolic Adaptations for Reproductive Success and Survival, Not For Thriving In Later Decades

Lieberman emphasizes that humans are not evolved for health or longevity but for reproduction. Natural selection’s sole interest is in maximizing reproductive success, not in ensuring health or longevity far past reproductive years. Consequently, many human adaptations are present not to enhance ongoing health, but to maximize the likelihood of having offspring.

Physiological Tradeoffs: Enhanced Reproductive Fitness vs. Long-Term Health Compromises

This reproductive focus creates physiological tradeoffs. Evolutionary adaptations, such as dietary preferences and metabolic processes, aim to improve reproductive fitness rather than ensuring robust health into old age. Modern mismatches occur when contemporary environments and diets interact with evolutionary traits not optimized for long-term well-being, creating risks for chronic diseases or health issues common in later life.

Evolutionary Constraints Explain why Ancestral Diets Don't Guarantee Modern Health

Lieberman also clarifies that ancestral diets themselves do not ensure ideal health for present-day humans. For example, the shift to agriculture brought about larger, more sedentary populations reliant on grain-based diets, which has been linked to declines in nutritional diversity and health, as seen in the archaeological record. However, Lieberman points out that much of the resulting health decline actually stemmed from the emergence of infectious diseases associated with denser populations and living alongside animals, rather than diet alone.

Even with these apparent health costs, farming diets allowed for dramatic population growth due to higher caloric output, despite higher vulnerability to famines and the rise of organized violence. This complexity underscores that evolutionary success in terms of population growth and reproduction often involves significant health and societal tradeoffs.

Humans Evolved As Omnivores Thriving On Diverse Diets, Not a Single Ancestral Diet

Analysis of 12 Hunter-Gatherer Societies Shows Diverse Diets From Plant to Animal Foods, All Maintaining Health, Indicating Humans Lack Specialization in Macronutrient Ratios

Lieberman highlights evidence from 12 hunter-gatherer groups with meticulously documented diets. Their eating patterns vary widely, with some groups subsisting mainly on plants and others on animal foods, and many blending both in various proportions. These groups maintain health across the spectrum, demonstrating that humans are ultimate omnivores and lack adaptations for any single ideal macronutrient ratio. This diversity refutes popular claims that there is one optimal ancestral diet for humans.

Evidence of Ancestral Humans Eating Grains and Legumes Contradicts Modern Paleo Diet Claims

Lieberman directly challenges the assertion—often made by modern paleo diet proponents—that ancestral humans did not eat grains or legumes. Paleontological evidence, such as grains and starches found on Neanderthal teeth, supports the inclusion of these foods in ancient diets. For example, among Kalahari hunter-gatherers, the marama bean—a type of legume—is their second most consumed food.

Ancient Legume Consumption Highlights the Discovery of Complementary Protein Combinations Like Rice and Beans for Adequate Amino Acid Intake, Not a Modern Agricultural Mistake

Lieberman further clarifies that combining legumes and grains, a hallmark of many traditional agricultural diets (such as rice and beans or Mediterranean combinations of bread with lentils or chickpeas), yields complementary amino acids essential for complete protein intake. The notion that such combinations are a ...

Strong Evidence for Mediterranean and Dash Diets Despite Cultural Specificity

The Mediterranean diet stands out with the strongest scientific support. The Predimed Study in Spain, which enrolled over 7,500 Spaniards assigned to either a Mediterranean diet incorporating olive oil or walnuts or a standard non-Mediterranean diet, was halted early due to the undeniable health benefits observed in the Mediterranean group—continuing was deemed unethical to the control group. Prospective, epidemiological, and mechanistic studies, including meta-analyses involving hundreds of thousands of individuals, consistently link the Mediterranean diet with reduced risks of cardiovascular diseases, cancer, and metabolic disorders. These repeated findings rank it among the most scientifically validated diets, although some argue its predominance in research is due in part to a Eurocentric focus.

Both the Mediterranean and DASH diets emphasize whole grains, legumes, fruits, vegetables, fish, and minimal refined carbohydrates. The Mediterranean diet is also characterized by healthy monounsaturated fats (from olive oil), omega-3 fats (from fish), and reduced added sugar, providing a constellation of healthy nutrients while avoiding deleterious processed foods. Success is attributed to both diet composition and intertwined lifestyle aspects, including sociability, underscoring that health benefits arise from a holistic pattern rather than one specific ingredient.

Studies: Plant-Based Diets Lead To Better Health Despite No Essential Nutrient Edge Over Omnivorous Diets

Recent meta-analyses and long-term cohort studies show that plant-based diets are linked to better health outcomes, including reduced risks of cancer and cardiovascular disease, particularly when compared to diets high in red meat. Epidemiological data demonstrate a dose-dependent relationship: each increment of red meat consumption further increases cancer risk, supported by mechanistic evidence. Red meat introduces carnitine, which gut bacteria convert to TMAO—an inflammatory molecule implicated in atherosclerosis. Another compound, Neu5Gc, unique to red meat, provokes an inflammatory immune reaction in all humans.

Despite their superior health associations, these benefits arise largely from the reduction of red meat rather than a biologically unique advantage of plant foods. Still, plant-based diets can fully provide all essential nutrients: soy is a source of complete plant protein, while combining legumes and grains covers all amino acids, and nuts supply key micronutrients. Well-constructed plant-based diets avoid the health pitfalls of refined carbohydrates and ultra-processed foods, which offer no clear advantage.

Carnivore and Low-carb Diets: Masculine Appeal and Simplicity Despite Lack of Superior Evidence

The carnivore (all-meat) and low-carb diet trends are driven in part by cultural associations with masculinity and the appeal of dietary simplicity, as exemplified by anecdotes like James Blunt’s attempt to improve manliness through all-meat eating—resulting in scurvy. Though people seeking quick benefits from processed diets may initially feel better, robust evidence for the superiority of these diets is lacking.

Low-carb diets tend to result in slightly more weight loss than low-fat diets in controlled ("efficacy") settings, but this advantage nearly disappears in more "effective" real-world studies due to poor long-term adherence and hunger. The carbohydrate-[restricted term] model explains how low-carb diets lower [restricted term], promoting fat mobilization and storage reduction, but numerous biological pathways can mediate weight loss, and the benefits are limited by the sustainability challenges many dieters face.

Paleo Diets Misuse Evolutionary Logic Via Naturalistic Fallacy but Correctly Suggest Avoiding Refined Foods

The paleo diet is based on the fallacious assumption that there is an ideal evolutionary diet, but archaeological evidence contradicts this, demonstrating that ancient humans consumed a diverse array of foods, including grains and legumes. While the avoidance of refined modern foods is sound advice, the premise against legumes and grains is flawed; supposed “anti-nutrients” like lectins and phytates are neutralized by cooking or fermentation. Populations with high longevity, such as in Japan, clearly thrive on diets rich in cooked beans and grains.

The paleo exclusion of dairy after weaning is also contradicted by the evolution of lactase persistence and the nutritional utility of fermented dairy products. Thus, though the paleo movement is correct in warning against processed foods, its claims about ancient diets and anti-nutrients are not supported by either archaeological or medical evidence.

Blue Zone Marketing Exemplifies how Manipulation and Poor Documentation Undermine Longevity Claims

Claims about Blue Zones—regions reputed for extreme longevity—are undermined by unreliable documentation: only 18% of reported centenarians in these areas have birth certificates, making self-reported ages and thus longevity claims highly dubious. Small pockets with extraordinary centenarian rates may reflect statistical outliers or even insurance fraud rather than genuine diet-induced longevity.

The most prominent U.S. Blue Zone, Loma Linda, California, owes its longevity to lifestyle patterns such as regular exercise, vegetarianism, and abstaining from smoking, rather than any specific diet. There is no single dietary pattern proven to ensure longevity, environmental sustainability, disease prevention, and satisfaction for everyone. The idea of an “optimal diet,” as often marketed, lacks scientific credibility and is more salesmanship than science.

Raw Food Diets Reflect Misguided Evolutionary Beliefs Causing Unsustainable Nutritional Stress Without Modern Supplements

Raw food diets are predicated on a misunderstanding of human evolution, ignoring the essential role cooking played in human development. Raw food diets are unsustaina ...

Daniel Lieberman and Chris Williamson discuss how a combination of educational, regulatory, and structural interventions can help improve dietary health without excessively restricting individual freedom. They highlight the need for better information, practical education, and systemic reforms to counteract the profit-driven food environment, which undermines personal responsibility and public health alike.

Educational and Regulatory Interventions Can Enhance Food Choices Without Restricting Freedom

Lieberman uses England's traffic-light food labeling system as an example of a simple, effective intervention. Green, yellow, and red labels quickly communicate the relative health value of foods, enabling informed choices without prohibiting the purchase of less healthy items. Despite their practicality, these labeling systems face industry resistance, and their adoption elsewhere is limited.

He emphasizes the lack of thorough nutritional education, noting that even medical schools devote little attention to this topic. Lieberman argues for integrating nutritional literacy into the standard curriculum—teaching macronutrient chemistry, the effects of food processing, and ingredient recognition. He proposes teaching the chemistry of food alongside traditional subjects, empowering people to discern between, for example, saturated and unsaturated fats or processed and whole foods. Lieberman notes that this knowledge is not especially complex and should be accessible to all, not just specialists.

Another approach Lieberman suggests is taxing ultra-processed foods and sugary products, drawing a parallel with cigarette taxes. Such economic incentives discourage unhealthy choices without outright bans. However, these policies often meet strong resistance from the food and beverage industry, as seen in Mexico, where an attempted soda tax was overturned following pressure from major corporations like Coca-Cola. Lieberman acknowledges the need for public debate about such measures, as the health impact of cheap ultra-processed foods is a broad societal concern.

Lieberman also calls for regulatory measures requiring clear disclosure of ultra-processed ingredients, to counteract misleading claims commonly found on packaging. For example, fruit roll-ups often advertise benefits like being "made with real fruit" and "filled with vitamin C," yet are essentially candy, stripped of fiber, and nutritionally misleading. More transparent labeling would allow consumers to make better-informed decisions, rather than relying on deceptive marketing.

Agency Within Constraints Requires Knowledge and Structural Support

Lieberman stresses that while individual responsibility is important, agency is difficult without knowledge and structural support. Many people would like help making healthier choices, but the food system creates an environment engineered to pr ...