HoldsUp

Daniel Lieberman

Harvard University

Daniel Lieberman is a professor of human evolutionary biology, paleoanthropologist, and author at Harvard. His published research focuses on the biomechanics and energetics of human physical activity, including studies on running kinematics, footwear, and metabolic rates. He also investigates the physiological and metabolic impacts of exercise, such as energy expenditure, myokine secretion, and disease prevention.

67 claims checked on air: 5 context 5 contradicted 7 overstated 41 supported 9 unverified

What they said on air - supported

1 citing their own research

0:06:48supportedmoderateHarvard Professor: “I Tried Every Diet. This Is By Far The W

Large-scale meta-analyses and long-term studies show that plant-based diets generally yield better health outcomes than animal-heavy diets.

"when you look at the data and you look at like big meta-analyses, large-scale studies, I don't think there's much contest that, you know, plant-based diets of various sorts—and they're not all the same—tend to have better health outcomes in terms of meta-analyses, long-term studies, and there's also mechanistic data as well." (said at 0:06:48)

Large-scale systematic reviews, meta-analyses, and prospective cohort studies show that plant-based diets and higher intake of plant protein relative to animal protein are associated with lower all-cause and cause-specific mortality (including cardiovascular disease and cancer mortality). Meta-analyses also note nuances, such as the quality of plant foods (healthy vs. unhealthy plant-based diet indices), consistent with the speaker's statement that plant-based diets 'are not all the same.' Evidence from observational prospective cohorts is graded moderate certainty overall.

0:07:38supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

Carnitine from meat is converted by gut bacteria into TMAO, an inflammatory molecule mechanistically linked to atherosclerosis and elevated blood pressure.

"meat has a protein called carnitine, and carnitine, when it goes to your gut, is transformed into another molecule called TMAO... And TMAO is a known inflammatory molecule that causes inflammation and has been associated with risk of actually it's been shown to be mechanistically related to atherosclerosis, to hardening of the arteries, to increased blood pressure." (said at 0:07:38)

Published studies confirm that dietary L-carnitine (an amino acid derivative abundant in red meat) is metabolized by intestinal microbiota into trimethylamine (TMA), which is oxidized in the liver to form trimethylamine N-oxide (TMAO). Mechanistic research in animal models demonstrates that TMAO promotes atherosclerosis and vascular inflammation, while randomized dietary interventions and prospective cohort studies in humans show that dietary red meat significantly elevates circulating TMAO levels and increases cardiovascular disease risk.

0:09:05supportedmoderateHarvard Professor: “I Tried Every Diet. This Is By Far The W

Saturated fat intake raises atherogenic lipoprotein levels in individuals possessing specific genetic susceptibilities.

"Some of us can eat as much saturated fat as we want, and it doesn't really have any negative effect, but others do have some genetic susceptibility to saturated fat, and it does raise their their risk of raise the levels of of lipoproteins or cholesterol molecules that cause heart disease." (said at 0:09:05)

Published randomized dietary interventions and gene-diet interaction studies confirm that interindividual variability in low-density lipoprotein (LDL) cholesterol and apolipoprotein B responses to saturated fat intake is significantly modified by specific genetic variants, notably polymorphisms in apolipoprotein E (APOE) and other lipid-metabolizing genes.

0:12:52supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

Participants tracked in the National Weight Control Registry have maintained their weight loss for an average of approximately 5.6 to 6 years.

"There's something called the National Weight Control Registry where they've actually analyzed, again, because you can't randomize huge numbers of people to different kinds of diets perfectly, so what this study has done is that they've looked at they've tracked people who managed to lose weight and keep it off for a long period of time. I think the average for the respondents is at least six years or something like that, 5.6 years or something like that." (said at 0:12:52)

The claim that participants in the National Weight Control Registry (NWCR) have maintained their weight loss for an average of approximately 5.6 to 6 years is supported by published studies of the NWCR cohort. Across multiple publications describing the registry enrollees, the average duration of maintained weight loss at enrollment is reported between 5.1 and 5.8 years (frequently reported as an average of 5.5 or 5.8 years).

0:14:45supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

The human body can convert fats and proteins into glucose (sugars).

"your body can transform fats and proteins into sugars." (said at 0:14:45)

The human body synthesizes glucose from non-carbohydrate precursors via gluconeogenesis, primarily in the liver and kidneys. Glucogenic amino acids derived from dietary or endogenous protein breakdown, as well as the glycerol backbone of triglycerides (fats) and odd-chain fatty acids, are established substrates for endogenous glucose production.

0:15:05supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

Protein requires more energy to digest than other macronutrients.

"Protein takes a little bit more energy to digest and and it's pretty nutritious." (said at 0:15:05)

The claim that protein requires more energy to digest than other macronutrients is supported by nutritional research. The energy expended to digest, absorb, and metabolize nutrients is known as the thermic effect of food (TEF) or diet-induced thermogenesis. Protein has a consistently higher thermic effect than either carbohydrates or fats.

0:17:50supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

Soy contains all essential amino acids and is a complete protein capable of supporting human nutritional requirements without meat.

"soy is a complete protein. You could actually live your life off soy. You don't actually need to eat meat in order to get protein." (said at 0:17:50)

Soy protein is well established in nutritional science as a high-quality, complete plant protein. It contains all nine essential amino acids in proportions that satisfy human physiological requirements across the lifespan. Using standard protein quality evaluation metrics such as the Protein Digestibility-Corrected Amino Acid Score (PDCAAS), isolated soy proteins and concentrates achieve scores near or equal to 1.00 (the maximum score, comparable to dairy and egg proteins), confirming that human protein and essential amino acid requirements can be fully met without meat.

0:22:00supportedmoderateHarvard Professor: “I Tried Every Diet. This Is By Far The W

In a randomized trial in Spain with over 7,500 participants (PREDIMED), the Mediterranean diet intervention was halted after roughly 5 years because the cardiovascular benefits were so pronounced that continuing the control diet was deemed unethical.

"one of the biggest studies was one done in Spain, for example, where they had over 7,500 Spaniards, and they assigned some of them a Mediterranean diet where they had to have olive oil or or walnuts—there were two arms to that—versus Spaniards who were not eating a Mediterranean diet. And after I think after 5 years, they stopped the study because the effects, the beneficial effects of the Mediterranean diet were so high that they felt that it was unethical to continue the study" (said at 0:22:00)

The PREDIMED multicenter randomized trial enrolled 7,447 participants at high cardiovascular risk in Spain, randomizing them to a Mediterranean diet supplemented with extra-virgin olive oil, a Mediterranean diet supplemented with mixed nuts, or a control diet (low-fat advice). After a median follow-up of 4.8 years, the trial was stopped early based on a prespecified interim analysis showing a statistically significant ~30% reduction in major cardiovascular events in both Mediterranean diet groups compared to the control group. Protocol irregularities related to randomization led to retraction and re-analysis in 2018, which confirmed the primary findings.

0:31:00supportedmoderateHarvard Professor: “I Tried Every Diet. This Is By Far The W

A typical American supermarket stocks around 40,000 distinct food items, and more than 50% of them are ultra-processed foods.

"the typical American supermarket has 40,000 different kinds of food. 40,000. It's kind of amazing. And over 50% of that is ultra-processed, designed to be highly appealing, addictive, convenient, inexpensive" (said at 0:31:00)

Industry retail data (such as benchmarks from the Food Marketing Institute) consistently estimates that an average US supermarket carries between 30,000 and 40,000 distinct items. Regarding the level of processing in the US retail supply, a comprehensive cross-sectional study of 230,156 packaged food and beverage products in the US (representing >80% of all products sold) classified 71% of products as ultra-processed according to the NOVA classification system, well exceeding the 50% threshold stated in the claim.

0:31:54supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

Refining flour by removing the outer layers and germ removes substantial amounts of the grain's protein and fiber.

"So when you take flour and you refine it, right, you remove the outer layers and you remove the germ, you're removing a lot of the protein and you're removing a lot of the fiber." (said at 0:31:54)

Refining flour by removing the outer bran layer and the germ significantly reduces both dietary fiber and protein content compared to whole wheat flour. During conventional milling to produce white flour, the fibrous outer bran layers and nutrient-dense germ are removed, leaving mostly the starchy endosperm. Studies evaluating milling fractions show marked reductions in fiber and protein when comparing whole wheat flour to refined white flour.

0:36:45supportedmoderateHarvard Professor: “I Tried Every Diet. This Is By Far The W

In Blue Zones, the proportion of centenarians is approximately 6 per 10,000 compared to 3 per 10,000 in the United States.

"So it's like six people out of 10,000, as opposed to in the United States where it's three people out of 10,000." (said at 0:36:45)

The speaker's figures closely reflect demographic estimates of centenarian prevalence. In demographic studies evaluating longevity hotspots and Blue Zones, centenarian prevalence typically ranges from approximately 5 to 13 per 10,000 inhabitants (50 to 130 per 100,000), such as observed in validated clusters in Sardinia, Okinawa, and related regions. In contrast, the nationwide prevalence of centenarians in the United States has historically hovered around 2 to 3 per 10,000 inhabitants.

0:43:16supportedhightheir own paperHarvard Professor: “I Tried Every Diet. This Is By Far The W

A comprehensive review paper on the carbohydrate-insulin model of obesity was published in the American Journal of Clinical Nutrition.

"But in fact, I'm one of the co-authors of the carbohydrate-insulin model big paper that was recently in the American Journal of Clinical Nutrition." (said at 0:43:16)

A major review and perspective paper detailing the carbohydrate-insulin model of obesity ('The carbohydrate-insulin model: a physiological perspective on the obesity pandemic') was published in The American Journal of Clinical Nutrition in 2021.

0:47:26supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

The DASH diet was originally developed by the National Institutes of Health (NIH).

"DASH stands for Dietary Approaches to Stop Hypertension. So it was originally developed for... blood pressure, but it turns out to be a low-fat diet, and it's actually probably the second-most studied diet after Mediterranean. It's very well studied. So it was developed by NIH" (said at 0:47:26)

The Dietary Approaches to Stop Hypertension (DASH) dietary pattern was developed and evaluated in multicenter clinical trials sponsored and funded by the National Institutes of Health (specifically the National Heart, Lung, and Blood Institute, NHLBI) to test whether dietary patterns rich in fruits, vegetables, and low-fat dairy products with reduced saturated fat could lower blood pressure.

0:50:06supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

Physical activity enhances muscle insulin sensitivity, leading to lower insulin secretion in response to a given quantity of carbohydrate.

"when people are very physically active, it changes the insulin sensitivity of their muscles so that they're um so that you actually produce less um you actually produce less insulin for a given amount of carbohydrate." (said at 0:50:06)

The speaker's statement accurately describes a core principle of exercise physiology and glucose homeostasis. Regular physical activity and exercise training enhance skeletal muscle insulin sensitivity, increasing insulin-stimulated glucose uptake and disposal. Because tissues respond more efficiently to insulin, the pancreatic beta cells require less insulin secretion to clear a given carbohydrate or glucose load, thereby reducing postprandial hyperinsulinemia.

0:52:38supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

Monounsaturated and polyunsaturated fats lower the risk of cardiovascular disease.

"So polyunsaturated, monounsaturated fats are are risk-lowering fats." (said at 0:52:38)

A broad body of evidence from randomized controlled trials and prospective observational studies demonstrates that polyunsaturated and monounsaturated fats lower cardiovascular disease (CVD) risk, particularly when replacing saturated fats or refined carbohydrates. A Cochrane systematic review of 15 randomized controlled trials (56,675 participants) found that reducing saturated fat and replacing it with polyunsaturated fat reduced cardiovascular events by 17% (RR 0.83, 95% CI 0.70 to 0.98). Similarly, the American Heart Association Presidential Advisory on dietary fats concluded that replacing saturated fats with unsaturated fats (particularly polyunsaturated and monounsaturated vegetable oils) lowers LDL cholesterol and reduces CVD incidence.

0:54:26supportedmoderateHarvard Professor: “I Tried Every Diet. This Is By Far The W

In the University of Wisconsin macaque calorie restriction study, the control group macaques were fed an ad libitum diet high in refined sugars.

"So, do you know there's there was a big study that was done in um in um was Wisconsin where they took a whole bunch of macaques, right? And they gave uh one group of macaques a calorie-restricted diet and another group of macaques—and this is a 20-year long study... But guess what? When people looked at the data, the non-calorie restricted macaques were basically being fed a crap food diet. They were getting lots of sugary foods. They were getting obese. They were, you know, they were not healthy normal macaque diets. They were fed an ad libitum crap diet." (said at 0:54:26)

The speaker accurately describes the dietary differences identified in the long-term nonhuman primate calorie restriction (CR) trials. In comparative analyses between the University of Wisconsin (UW) and National Institute on Aging (NIA) rhesus macaque studies (such as Mattison et al., 2017), researchers documented that the UW study fed monkeys a purified, semi-synthetic diet high in refined sucrose (approximately 28.5% of the diet) with ad libitum access for control animals. This dietary formulation contributed to higher rates of obesity, diabetes, and metabolic dysfunction in the control group compared to the NIA study, which used a portion-controlled, natural-ingredient diet with substantially lower refined sugar content.

0:56:09supportedvery lowHarvard Professor: “I Tried Every Diet. This Is By Far The W

Caloric restriction reliably extends lifespan in model organisms including yeast and fruit flies, but its effect on lifespan varies across different mouse strains.

"So, yes, it is true that for some species, for some um mouse lines, but not all, caloric restriction has been shown to improve their lifespan, but not all of them, by the way. Um certainly true for yeast, certainly true for fruit flies" (said at 0:56:09)

Extensive literature in model organisms demonstrates that dietary and caloric restriction (CR) robustly extends lifespan in invertebrate models such as the yeast Saccharomyces cerevisiae and the fruit fly Drosophila melanogaster. Furthermore, research in mice shows that the lifespan response to caloric restriction is strongly genotype-dependent: in a study evaluating 40% caloric restriction across 41 recombinant inbred mouse strains, lifespan was extended in some strains, unaffected in others, and shortened in a substantial subset of strains.

0:57:22supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

Intermittent fasting and caloric restriction downregulate mTOR signalling and upregulate AMPK signalling, shifting cells from growth to repair mode.

"there's another pathway that's turned on by another big gene called AMPK. Um and AMPK is like your repair gene. And what happens when you go through intermittent fasting or calorie restriction is that you turn down or turn off the mTOR and turn up the AMPK. So you're turning off growth and you're turning up repair." (said at 0:57:22)

The speaker's statement accurately reflects established nutrient-sensing biology. Intermittent fasting and dietary restriction reduce nutrient availability, leading to the inhibition of mammalian target of rapamycin (mTOR) signaling (which normally drives cell growth and protein synthesis) and the activation of AMP-activated protein kinase (AMPK) signaling, which promotes cellular maintenance, mitochondrial rejuvenation, and repair processes like autophagy.

1:03:02supportedmoderateHarvard Professor: “I Tried Every Diet. This Is By Far The W

Intermittent fasting alternates the body between positive and negative energy balance, activating and deactivating mTOR and AMPK through metabolic switching.

"Well, again, intermittent fasting moves your body in and out of what's we call positive and negative energy balance, therefore turning on and off mTOR and AMPK. It's called metabolic switching." (said at 1:03:02)

The speaker's statement accurately describes the established cellular and metabolic dynamics of intermittent fasting. Fasting induces a negative energy state that triggers metabolic switching (from glucose utilization to fatty acid oxidation and ketogenesis), activating the cellular energy sensor AMP-activated protein kinase (AMPK) and inhibiting the mechanistic target of rapamycin (mTOR). Conversely, postprandial refeeding shifts the body into positive energy balance, downregulating AMPK and activating mTOR to support cellular growth and repair.

1:07:51supportedmoderateHarvard Professor: “I Tried Every Diet. This Is By Far The W

Dental calculus evidence shows Neanderthals consumed grains and plant starches.

"We have paleontological evidence. We have Neanderthals with grain starch things on their teeth." (said at 1:07:51)

Analysis of dental calculus (calcified plaque) from Neanderthal fossil remains directly demonstrates the presence and consumption of plant starches and grass/grain seeds. In a landmark study published in PNAS, researchers recovered starch grains and phytoliths from the dental calculus of Neanderthal specimens from Shanidar Cave (Iraq) and Spy Cave (Belgium). These microfossils included starch grains from grass seeds (Triticeae family), legumes, and date palms, with many showing signs of thermal alteration characteristic of cooking.

1:10:50supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

Anti-nutrients bind to dietary vitamins and minerals in the digestive tract and inhibit their absorption.

"anti-nutrients are compounds that like bind to vitamins and minerals and and prevent us from absorbing them." (said at 1:10:50)

The speaker's statement accurately describes the definition and primary mechanism of dietary anti-nutrients. Anti-nutritional factors (such as phytic acid/phytates, oxalates, tannins, and lectins) are naturally occurring plant compounds that bind, chelate, or complex with essential dietary minerals (such as iron, zinc, and calcium) and other micronutrients in the gastrointestinal tract, forming insoluble complexes that significantly inhibit their bioavailability and intestinal absorption.

1:11:00supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

Cooking and fermentation reduce anti-nutritional factors in foods such as legumes and grains to harmless levels.

"If you cook your food or you ferment your food, you get rid of the anti-nutrients." (said at 1:11:00)

Thermal processing (cooking) and fermentation are well-established methods for substantially reducing or eliminating antinutritional factors (such as phytates, lectins, tannins, and trypsin inhibitors) in legumes and cereal grains. Cooking denatures heat-labile antinutrients such as lectins and protease inhibitors, while fermentation utilizes microbial enzymatic activity (such as phytases) and organic acid production to degrade phytates and polyphenols by up to 90% to 100%, thereby markedly improving mineral bioaccessibility and protein digestibility.

1:12:54supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

Cooking foods increases net energy yield and nutrient availability by breaking down plant and animal cell walls.

"Cooking increases how much energy you get from food. It actually Cooking releases nutrients from food." (said at 1:12:54)

Cooking increases the net energy yield and nutrient availability of food. Thermal processing gelatinizes starches, denatures proteins, and alters cellular structures, which enhances digestibility and reduces the energetic metabolic cost of digestion. Controlled feeding studies in animal models and human physiological research demonstrate that cooking meat, tubers, and lipid-rich plant foods yields significantly greater net metabolizable energy compared to equivalent raw foods.

1:14:52supportedmoderateHarvard Professor: “I Tried Every Diet. This Is By Far The W

Hominins began cooking up to 1 million years ago, and evidence indicates cooking became widespread by 400,000 years ago.

"our species started cooking maybe a million years ago. Certainly by 400,000 years ago, cooking became extremely common among our ancestors" (said at 1:14:52)

Archaeological records support both parts of the claim. Microstratigraphic and spectroscopic analysis of intact Acheulean sediments at Wonderwerk Cave in South Africa provides unambiguous evidence of in situ fire use—including burned bone and ashed plant remains—dating to approximately 1.0 million years ago. Furthermore, archaeological syntheses show that widespread, regular use of fire emerged and diffused across hominin populations in Africa and western Eurasia starting around 400,000 years ago.

1:19:12supportedmoderateHarvard Professor: “I Tried Every Diet. This Is By Far The W

In behavioral experiments, chimpanzees preferentially choose cooked foods over raw foods.

"there are these fun experiments where they give chimpanzees the opportunity to choose between cooked food and raw food. And even though chimpanzees don't cook their food, they usually prefer the cooked food." (said at 1:19:12)

Experimental studies evaluating the cognitive foundations of cooking have demonstrated that chimpanzees (Pan troglodytes) spontaneously prefer cooked foods over raw foods when presented with a choice between the two, even willing to pay temporal costs or exchange raw food to obtain cooked alternatives.

1:19:59supportedmoderateHarvard Professor: “I Tried Every Diet. This Is By Far The W

The archaeological record indicates human health markers declined with the advent of farming, largely due to increased infectious disease from cohabiting with animals and higher population density.

"And if you look in the archaeological record, once farming starts, people's health declined. But the reason for most of those declines in health was because of infectious disease, because several things happened. First is we started living with animals, right? So we were living with our sheep and our cows and whatever. We started getting diseases from those animals." (said at 1:19:59)

Bioarchaeological and paleopathological evidence broadly supports the claim that health markers deteriorated across many human populations during the transition from foraging to agriculture (often termed the First Epidemiological Transition). Skeletal remains from early farming settlements consistently exhibit increased indicators of physiological stress, infection, and chronic disease. This decline in health is widely attributed to the combined effects of sedentism, higher population density, nutritional shifts, and increased transmission of zoonotic pathogens resulting from close contact with domesticated herd animals.

1:30:03supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

When weight is lost, adipocytes shrink in volume rather than being eliminated entirely.

"Once you create fat cells, you can't get rid of the fat cells; they only empty themselves. Is that correct? That's correct for the most part, yeah. The fat cells swell, and so what you're doing is reducing" (said at 1:30:03)

The claim that weight loss reduces adipocyte volume (cell size) rather than eliminating fat cells (adipocyte number) is supported by scientific evidence. Studies using 14C bomb-test dating demonstrated that total adipocyte number remains constant in adulthood even after marked weight loss, indicating that changes in adipose mass are primarily driven by changes in fat cell volume (lipid content) rather than changes in total cell number (PMID: 18454136). Furthermore, long-term studies in individuals undergoing significant weight loss (such as via bariatric surgery) confirm that substantial weight reduction significantly decreases adipocyte volume without altering the total number of subcutaneous fat cells (PMID: 24760260).

1:31:25supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

When fat mass is lost, shrinking adipocytes decrease leptin secretion, signaling the brain to stimulate appetite.

"they're also producing less of a hormone called leptin, which is now telling your brain, "We're losing energy. You need to eat more to replace us." So it's called—we call it the leptinostat. So the fat cells—when you lose fat, the fat cells send a signal to your body to eat more." (said at 1:31:25)

The speaker accurately describes the classic adipostatic feedback loop (often termed the 'adipostat' or 'leptinostat'). Leptin is an adipokine secreted by adipose tissue in proportion to fat mass. When adipose tissue mass decreases (such as during caloric restriction or weight loss), circulating leptin levels fall markedly. This decline in leptin signaling to hypothalamic regulatory circuits removes central inhibition on orexigenic pathways, leading to increased appetite, hunger, and reductions in energy expenditure to defend baseline fat stores.

1:38:20supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

Performing physical activity prior to eating reduces the amount of insulin secreted in response to a meal.

"had I gone running this morning and I just had lunch, the amount of insulin I would have produced from the taco that I had in the airport would have been less than the fact that I didn't go running this morning." (said at 1:38:20)

Acute physical activity performed prior to a meal improves insulin sensitivity and stimulates insulin-independent glucose uptake via skeletal muscle contraction, which attenuates postprandial glucose and insulin excursions compared to remaining sedentary prior to eating.

1:39:32supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

Wilbur Atwater established the caloric conversion values of approximately 4.1 calories per gram of carbohydrate and protein and 9 calories per gram of fat.

"This formula was created by a guy named Wilbur Atwater, who analyzed more poop than you can imagine. But anyway, Wilbur Atwater was a professor in Connecticut who came up with these—and what they do is you take some food and you separate out the carbohydrates, the fats, and the protein. And then you use a formula: 4.1 calories per gram of carb, 4.1 calories per gram of protein, and 9-something for the fat." (said at 1:39:32)

Wilbur Olin Atwater developed the foundational system for calculating the metabolizable energy of macronutrients using human bomb calorimetry and balance studies measuring energy losses in feces and urine. The resulting Atwater factors establish the standard energy conversion values of approximately 4 kcal/g (or 4.1 kcal/g) for carbohydrates and proteins and 9 kcal/g (or 9.3 kcal/g) for fats.

1:41:09supportedvery lowHarvard Professor: “I Tried Every Diet. This Is By Far The W

Stephen Secor's research on boa constrictors showed that ground rats require significantly less diet-induced thermogenesis to digest than whole rats.

"one of my favorite experiments is a guy named Stephen Secor at the University of Alabama who studies what's called diet-induced thermogenesis... You give it the same rat or the exactly the same size rat, but this time he grinds it up. Same rat, same amount of calories, ground rat. And the boa constrictor slips right through his digestive system. It doesn't heat up at all or much less so because the boa constrictor is getting way more energy from that rat." (said at 1:41:09)

The core finding described by the speaker is supported by published research from Stephen Secor and colleagues (Boback et al., 2007), though with minor species and diet differences compared to the podcast description. The study examined Burmese pythons (Python molurus), rather than boa constrictors, fed intact or ground beef (not whole vs. ground rats). Grinding raw meat decreased specific dynamic action (SDA / diet-induced thermogenesis) by 12.4%, cooking reduced it by 12.7%, and the combination of cooking and grinding reduced it by 23.4%, demonstrating that processing meat significantly decreases the metabolic energy required for digestion. Because this claim is based on animal physiology experiments in reptiles, certainty is graded as very low.

1:42:09supportedmoderateHarvard Professor: “I Tried Every Diet. This Is By Far The W

Short-chain fatty acids produced from fiber fermentation by the gut microbiome can account for around 10% of total dietary energy uptake in some people.

"So all those bacteria that are once the celery passes through your, you know, the fiber from the celery passes into your colon, they're all these happy bacteria and they're delighted that you had the celery and they're breaking that celery down into what's called short-chain fatty acids of which you which you then up take up into your bloodstream and then you use. So we think actually that for some people maybe about 10% of the energy that they get from their food is not even measured on those nutrition facts labels because it comes from our microbiome." (said at 1:42:09)

The claim is supported by nutritional and physiological research on human colonic fermentation. Dietary fiber and resistant starches that pass undigested into the large intestine are fermented by gut microbiota into short-chain fatty acids (SCFAs), which are absorbed and utilized as an energy source. Classic metabolic estimations and reviews indicate that colonic microbial fermentation supplies roughly 5% to 10% of total daily energy requirements in humans.

1:47:25supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

Controlled human feeding studies show that increasing dietary intake of omega-6 fatty acids does not increase systemic inflammation.

"However, people have done studies, they give people like you and me, they go go sit in a lab, they give people omega-6 fatty acids and then measure whether their metabolism does that. Turns out that doesn't. There's no evidence and and there are quite a few studies, my book cites them, you can go look them up where where the the the increasing the amount of omega-6 fatty acids actually increases inflammation." (said at 1:47:25)

Systematic reviews and meta-analyses of randomized controlled intervention trials in humans show that increasing dietary intake of omega-6 polyunsaturated fatty acids (such as linoleic acid) does not increase circulating levels of systemic inflammatory markers, including C-reactive protein (CRP), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), fibrinogen, or adhesion molecules.

1:47:35supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

Omega-6 fatty acids can be biochemically converted in the body into arachidonic acid, which can subsequently be metabolized into inflammatory prostaglandins.

"the omega-6 fatty acids can be turned into a by your digestive system into another thing called arachidonic acid, which can then be turned into an inflammatory compound like a prostaglandin" (said at 1:47:35)

The biochemical pathway described by the speaker is well established. Dietary omega-6 polyunsaturated fatty acids, primarily linoleic acid, undergo elongation and desaturation in human tissues to form arachidonic acid. Arachidonic acid incorporated into cell membrane phospholipids can subsequently be released and metabolized by cyclooxygenase (COX) enzymes into 2-series prostaglandins (such as prostaglandin E2), which function as potent mediators of inflammation.

1:47:57supportedmoderateHarvard Professor: “I Tried Every Diet. This Is By Far The W

Large prospective cohort studies, such as the Nurses' Health Study, show that higher intake of omega-6 fatty acids is associated with lower risks of heart disease and cancer.

"There's now epidemiological studies as well which show that people who eat a lot of omega-6 fatty acids do really well. In fact, people eat in fact omega-6 fatty acids have been shown to be more preventive like the Nurses' Health Study and various other big huge studies. We're talking hundreds of thousands of people, prospective studies over decades, actually have lower risks of heart disease, cancers, etc. than people who don't eat them." (said at 1:47:57)

Large prospective cohort analyses, including findings from the Nurses' Health Study and the Health Professionals Follow-up Study tracking over 120,000 individuals over several decades, demonstrate that higher dietary intake of omega-6 polyunsaturated fatty acids (such as linoleic acid) is associated with lower overall mortality and lower risk of death from major chronic conditions, including cardiovascular disease and cancer.

1:52:36supportedmoderateHarvard Professor: “I Tried Every Diet. This Is By Far The W

Approximately 75% of people fail to maintain standard traditional weight-loss diets.

"Well again um there you know various studies uh have shown that a lot of the standard traditional diets people do fall off them um and they're the numbers run all over the place but yeah I would say that probably a reasonable estimate is about 75% of people fall off their diet." (said at 1:52:36)

Published literature on weight management and dietary interventions supports the estimate that roughly 75% to 80% of individuals fail to sustain traditional weight-loss diets over the long term. Landmark reviews of weight loss maintenance indicate that only approximately 20% of overweight individuals successfully lose at least 10% of their initial body weight and maintain that loss for a year or more, reflecting high rates of long-term non-adherence and weight regain across standard caloric restriction and traditional dietary programs.

1:54:31supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

GLP-1 receptor agonist medications can lead to a 25% loss in total body weight.

"Some people lose 25% of their body weight, and there are new ones being formulated that maybe even they've been more powerful." (said at 1:54:31)

Randomized controlled trials confirm that incretin-based medications and multi-receptor agonists can lead to body weight reductions of 20% to 25% or more in a substantial portion of individuals, and newer formulations show even greater weight-loss potency. In the phase 3 SURMOUNT-1 trial, adults receiving the dual GIP/GLP-1 receptor agonist tirzepatide achieved mean weight reductions of up to 20.9% at 72 weeks, with 57% of patients in the 15-mg group losing 20% or more of their body weight. Furthermore, a phase 2 trial of retatrutide (a newer triple GIP, GLP-1, and glucagon receptor agonist) demonstrated a mean weight reduction of 24.2% at 48 weeks with the 12-mg dose.

1:54:45supportedhighHarvard Professor: “I Tried Every Diet. This Is By Far The W

Rapid weight loss from GLP-1 medications and bariatric surgery leads to substantial loss of skeletal muscle mass.

"So, we published my colleagues and I published a paper in JAMA, the journal of the American Medical Association recently. One of the big concerns about about GLP-1s is that people not only lose fat, they also lose muscle and they and they seem to lose a lot of muscle. It's a bit like bariatric surgery too. Like when you lose a lot of weight really fast, uh people lose a lot of muscle and that can put you at serious risk of frailty" (said at 1:54:45)

Published systematic reviews and meta-analyses confirm that rapid and substantial weight loss induced by incretin-based therapies (such as GLP-1 receptor agonists) and bariatric surgery results in significant concurrent loss of fat-free mass (FFM) and skeletal muscle mass. A 2026 systematic review and meta-analysis of randomized trials found that FFM accounted for approximately 33.3% of total weight loss with incretin therapies (mean loss of 4.8 kg vs. placebo) and 34.2% with bariatric surgery (mean loss of 9.1 kg). Similarly, meta-analytic data for bariatric surgery show an average loss of over 8 kg of lean body mass at 12 months, with the majority occurring rapidly in the first 3 months postsurgery.

1:56:10supportedmoderateHarvard Professor: “I Tried Every Diet. This Is By Far The W

Approximately 60% of people who initiate GLP-1 agonist therapy discontinue the medication within one to two years.

"The last study I saw, and again, things may change because they're now oral versions of the pill. They're now there's now a pill version so you don't have to inject it. But something like 60% of people who have tried GLP-1s have quit them after a year or two. 60%." (said at 1:56:10)

Published real-world evidence from large electronic health record and pharmacy claims databases supports the claim that approximately 50% to 65% of patients discontinue GLP-1 receptor agonist therapy within one to two years of initiation. Studies and reviews evaluating real-world persistence report that one-year discontinuation rates often range between 40% and 67%, and two-year discontinuation rates reach approximately 64%, driven by gastrointestinal adverse effects, high out-of-pocket costs, medication shortages, and tolerability issues.

2:00:40supportedmoderateHarvard Professor: “I Tried Every Diet. This Is By Far The W

Most medical schools provide little to no formal curriculum training in clinical nutrition to medical students.

"most physicians are given very little training in nutrition. I teach my undergraduates more nutrition. I tell them in my their lectures, you're going to get more from me than you're going to get in medical school." (said at 2:00:40)

The claim is supported by national surveys and systematic reviews of medical curricula. A national survey of accredited US medical schools found that medical students received an average of only 19.6 total contact hours of nutrition instruction over their entire medical education, with only 25% offering a dedicated nutrition course and only 27% meeting the minimum 25-hour guideline recommended by the National Academy of Sciences. A 2019 systematic review across multiple countries similarly confirmed that clinical nutrition remains insufficiently incorporated into medical school education globally.

2:05:35supportedmoderateHarvard Professor: “I Tried Every Diet. This Is By Far The W

Very few children are deficient in vitamin C.

"Well, very few kids are vitamin C deficient." (said at 2:05:35)

Nationally representative population surveillance data confirm that vitamin C deficiency is rare in children. In the United States National Health and Nutrition Examination Survey (NHANES), children consistently exhibit the highest circulating serum vitamin C concentrations of any age demographic, resulting in very low rates of deficiency compared to adults and smokers.

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