HoldsUp

DavidPerlmutterMD · 2026-03-17 · David Perlmutter (host), Andrew Koutnik

The Fuel Myth: Rethinking Carbs, Brain Health, and Human Performance | Andrew Koutnik

46 research-tied claims examined: 1 contradicted 2 overstated 7 context 27 supported 3 corroborated online 6 unverified

1

Contradicted by research

1:08:19Andrew Koutnikcontradictedhigh

Consuming 120 grams of carbohydrates per hour during prolonged strenuous exercise suppresses fat metabolism to approximately 10% of total energy expenditure and shifts over 85% of fuel utilization to glucose, primarily from muscle glycogen.

"when they compare 120 g of carbohydrates per hour compared to just 25 g per hour, one at 120 g per hour, insulin was infinitely higher, okay? But you essentially blocked fat metabolism to around 10% of total energy substrate used during a prolonged strenuous form of exercise. And you expedited muscle glycogen breakdown. Over 85% of the fuel came from glucose and most of it from muscle glycogen." (said at 1:08:19)

The claim asserts that ingesting 120 g/h of carbohydrates during prolonged strenuous exercise "expedited muscle glycogen breakdown" and that "most of it [came] from muscle glycogen." In exercise physiology and tracer studies, exogenous carbohydrate ingestion does not expedite (accelerate) muscle glycogen breakdown; rather, exogenous carbohydrate increases exogenous carbohydrate oxidation and either spares endogenous glycogen stores (particularly liver glycogen and muscle glycogen) or leaves endogenous carbohydrate oxidation unchanged compared to lower doses. Isotope tracer studies evaluating 90–120 g/h carbohydrate ingestion demonstrate that high exogenous carbohydrate intake delivers substantial circulating fuel (exogenous oxidation reaching ~1.5–1.7 g/min), reducing reliance on endogenous stores rather than accelerating glycogen depletion.

2

Overstated

0:24:15Andrew Koutnikoverstatedmoderate

Ketogenic dietary interventions have been shown in meta-analyses published in JAMA Psychiatry to therapeutically address mental health disorders including anxiety disorders, schizophrenia, and bipolar disorder.

"We've known for recently its application in various neurological disorders with the emergence of pilot data and now meta-analysis in JAMA Psychiatry showing that these tools can be applied in settings like anxiety disorders, schizophrenia, bipolar." (said at 0:24:15)

A systematic review and meta-analysis on ketogenic diets for mental health outcomes was published in JAMA Psychiatry (PMID 41191382). However, the claim overstates its findings and scope in several key respects: first, the meta-analysis focused on depressive and anxiety symptoms, not schizophrenia or bipolar disorder. Second, while randomized controlled trials (RCTs) demonstrated modest improvements in depressive symptoms, meta-analysis of nine RCTs evaluating anxiety symptoms showed no statistically significant benefit (SMD -0.03; 95% CI -0.18 to 0.12), leading authors to conclude that evidence for anxiety remains inconclusive.

0:43:25Andrew Koutnikoverstatedmoderate

Diamox (acetazolamide) causes mild metabolic acidosis and increases SpO2, but reliably reduces cognitive and physical performance.

"Diamox is a mountain sickness drug that specifically causes mild metabolic acidosis and increases SPO2 levels for people to attenuate mountain sickness when you get to low oxygen levels... when you use something like Diamox, it lasts for multiple hours, but we also know it reliably reduces uh cognitive performance, it reliably reduces physical performance." (said at 0:43:25)

Acetazolamide (Diamox) is a carbonic anhydrase inhibitor used for acute mountain sickness (AMS) prophylaxis. The speaker accurately describes its physiological mechanisms: it induces mild (partially compensated) metabolic acidosis by promoting renal bicarbonate excretion, which stimulates central and peripheral chemoreceptors to increase ventilation and arterial oxygen saturation (SpO2). Evidence also supports that acetazolamide impairs physical/exercise performance at sea level and in several acute hypoxic settings (reducing VO2 max, power output, and time to exhaustion). However, claiming that it 'reliably reduces cognitive performance' is overstated; while acetazolamide frequently causes side effects such as paresthesias, somnolence, and perceived fatigue, robust clinical evidence does not demonstrate a consistent or reliable impairment of objective cognitive function.

7

Needs context

0:00:00Andrew Koutnikneeds contextmoderate

Athletes following a ketogenic diet did not experience deterioration in physical performance compared to those on a high-carbohydrate diet.

"What we found is that when athletes were either on a ketogenic diet or on a high carb diet, the ketogenic diet did not produce any deterioration in physical performance." (said at 0:00:00)

The claim that a ketogenic diet causes no deterioration in athletic performance compared to a high-carbohydrate diet requires important qualification. Systematic reviews and position stands show that the impact of a ketogenic diet is highly dependent on exercise intensity, duration, and adaptation time. For maximal strength, resistance training, and moderate-intensity endurance (such as VO2 max and time to exhaustion), evidence indicates performance is generally preserved compared to high-carbohydrate diets. However, for high-intensity endurance, exercise economy, and elite-level competition, ketogenic diets frequently result in performance decrements or reduced efficiency compared to carbohydrate-rich diets.

0:25:30Andrew Koutnikneeds contextmoderate

Administration of exogenous ketones without dietary changes improves cognitive retention during acute hypoxic exposure at altitudes between 15,000 and 20,000 feet.

"we've studied just the mere application of ketones independent of diet change and see profound effects in various conditions, including in extreme environments like high altitude hypoxic exposure for special operations command grant looking at the ability to improve resilience against hypoxia exposure. Anywhere between 15 to 20,000 foot altitude immediate exposure and it increased the ability to have retained cognition in these extreme environments." (said at 0:25:30)

Exogenous ketone supplementation (such as ketone monoesters) taken acutely without dietary changes has been shown in controlled laboratory studies to partially attenuate declines in specific cognitive and psychomotor functions—such as reaction time on vigilance tests and code substitution performance—during severe acute hypoxic exposure simulating altitudes of 15,000 to 20,000 feet (4,500 to 6,100 m). However, the evidence is domain-specific and mixed: several randomized trials have found that while exogenous ketones improve blood oxygen saturation or neural signaling under hypoxia, they do not consistently improve broader cognitive test batteries, complex task performance, or real-world field performance during high-altitude operations.

0:40:35Andrew Koutnikneeds contextvery low

Beta-hydroxybutyrate alters epigenetic gene expression through beta-hydroxybutyrylation and activates FOXO antioxidant genes.

"There's actually something called beta-hydroxybutyrylation, which is an epigenetic change... And one of those genes is is a FOXO gene, which specifically is an antioxidant-producing gene, which so as a way of actually causing anti or scavenging oxidative stress molecules." (said at 0:40:35)

Beta-hydroxybutyrate (βOHB) acts as an epigenetic regulator via both histone deacetylase (HDAC) inhibition and lysine beta-hydroxybutyrylation. In cellular and rodent models, βOHB increases histone acetylation at the Foxo3a promoter (via class I HDAC inhibition), upregulating FOXO3A transcription and conferring protection against oxidative stress. FOXO3A is a transcription factor that upregulates antioxidant enzymes (such as superoxide dismutase and catalase) rather than directly producing antioxidant molecules. While the speaker conflates beta-hydroxybutyrylation with the HDAC-inhibition-driven histone acetylation mechanism originally demonstrated for FOXO activation, βOHB is an established epigenetic regulator that enhances FOXO-mediated antioxidant pathways in preclinical models.

0:54:05Andrew Koutnikneeds contexthigh

In the 1960s, Jonas Bergström developed the percutaneous muscle biopsy technique and showed that glucose is stored in muscle as glycogen.

"It wasn't until the 1960s where a physician named Jonas Bergström discovered the ability to actually stick a syringe into the muscle and do something called a muscle biopsy, so, they called the Bergström muscle biopsy, where they actually suctioned out a piece of muscle. And what they were finding is, oh wow, lo and behold, when we pull out muscle and analyze that muscle tissue, glucose was being stored as something called glycogen." (said at 0:54:05)

The speaker accurately describes Jonas Bergström's introduction of the percutaneous needle muscle biopsy technique in the 1960s, which used a specialized needle and suction to obtain skeletal muscle samples in humans, revolutionizing the study of human exercise physiology and glycogen dynamics in vivo. However, the claim that this led to the initial discovery that glucose is stored in muscle as glycogen is historically inaccurate; glycogen and its role as a stored carbohydrate in liver and muscle had been established more than a century earlier (initially isolated by Claude Bernard in the 1850s and extensively characterized in muscle throughout the early 20th century). Bergström and colleagues used the biopsy technique to demonstrate how human muscle glycogen content fluctuates, depleting during exercise and supercompensating with dietary carbohydrate.

1:03:34Andrew Koutnikneeds contexthigh

In the medical literature, 70 mg/dL (3.9 mmol/L) is typically defined as the threshold for hypoglycemia because the majority of individuals experience symptoms at or below that level.

"in the medical literature 70 mg/dL or 3.9 mmol is usually the threshold for hypoglycemia. Why is it used as a threshold for hypoglycemia? Because the vast majority of people will experience symptoms at or below that level." (said at 1:03:34)

While 70 mg/dL (3.9 mmol/L) is widely established in clinical practice guidelines and consensus statements as the alert threshold for hypoglycemia, the physiological rationale given is inaccurate. Experimental clamp studies establishing the hierarchy of glycemic thresholds show that autonomic counterregulatory hormones (epinephrine, glucagon) begin to release at approximately 65–68 mg/dL, whereas autonomic symptoms (such as sweating, tremor, and palpitations) do not typically occur until glucose drops to approximately 55–58 mg/dL (and neuroglycopenic symptoms below ~50 mg/dL). The 70 mg/dL cutoff is selected as a safety threshold because it approximates the upper limit of physiological counterregulation, providing an early margin of safety to prevent symptomatic or neuroglycopenic hypoglycemia, rather than because symptoms occur at 70 mg/dL.

1:21:12David Perlmutter (host)needs contextlow

An analysis of Framingham Heart Study data published in the Journal of Prevention of Alzheimer's Disease found that consuming an average of one serving per day of ultra-processed foods was associated with a 13% increased risk of developing Alzheimer's over a 6-year period.

"A study came out evaluation of Framingham Heart Study uh data in the Journal of Prevention of Alzheimer's—what a journal. Can you imagine? Prevention of Alzheimer's. Indicating that over the 6-year period, averaging one serving a day, just one serving a day of ultra-processed foods, based upon what you and I've been talking about, was associated with a 13% increased risk of developing Alzheimer's during that 6-year period" (said at 1:21:12)

A prospective cohort study of 1,375 Framingham Heart Study Offspring participants published in The Journal of Prevention of Alzheimer's Disease found that each additional serving per day of ultra-processed food was associated with a 13% increased risk of Alzheimer's disease (HR = 1.13, 95% CI: 1.03–1.25) after adjusting for diet quality and metabolic risk factors. However, this association was observed specifically among participants who were under 68 years of age at baseline over a mean follow-up of 12.7 ± 6.0 years (dietary data were collected across examination cycles 5 and 7, approximately 6 years apart), and no significant association was found in older participants. Additionally, the 13% figure reflects an incremental risk per serving per day, not the absolute effect of consuming only a single serving.

1:21:41David Perlmutter (host)needs contextlow

An analysis of Framingham Heart Study data found that consuming 10 or more servings of ultra-processed foods per day was associated with a 2.7-fold increased risk of developing Alzheimer's disease.

"Having 10 or more servings of ultra-processed foods a day, it seems like a lot. You know as well as I do, that's not uncommon when you add in the soft drinks, the flavored yogurts, you name it, was associated with a 2.7-fold increased risk of developing Alzheimer's." (said at 1:21:41)

A prospective analysis of the Framingham Heart Study (PMID: 39863327) did report that consuming 10 or more servings per day of ultra-processed food was associated with a 2.7-fold increased risk of developing Alzheimer's disease (hazard ratio 2.71, 95% CI: 1.18–6.24). However, this specific finding was restricted to participants who were younger than 68 years of age at baseline; no statistically significant association was observed among participants aged 68 years or older, and the findings are observational.

27

Supported by research

0:00:15Andrew Koutniksupportedlow

Fat oxidation rates in keto-adapted athletes exceeded previously reported medical literature, with some athletes oxidizing over 1.85 grams of fat per minute during physical activity.

"fat metabolism made up the majority of fuel substrate during this activity at a level of fat oxidation that was higher than any fat levels ever reported in the medical literature. Some athletes were over 1.85 g of fat burned per minute during physical activity." (said at 0:00:15)

In the FASTER study (Volek et al., 2016), investigators evaluated 20 elite ultra-endurance runners adhering to either a traditional high-carbohydrate diet or a long-term low-carbohydrate ketogenic diet. Keto-adapted athletes achieved mean peak fat oxidation rates of 1.54 ± 0.18 g/min (with individual peak values exceeding 1.8 g/min), compared to 0.67 ± 0.14 g/min in high-carbohydrate runners. Fat oxidation accounted for an average of 88% of total energy expenditure during submaximal exercise, representing the highest fat oxidation rates documented in exercise physiology literature. The evidence is rated low certainty due to the cross-sectional design and small sample size (n=20).

0:13:29Andrew Koutniksupportedhigh

Starting a ketogenic diet lowers blood glucose and insulin levels, causing an immediate loss of water weight followed by an automatic reduction in caloric intake.

"when people get on to a ketogenic diet, they almost immediately—they're lowering their glucose, which causes a lowering of insulin, and essentially that causes a cascade of events, which you drop water weight, so you essentially lose weight almost instantly. Then, by default, the evidence shows that people volitionally reduce their caloric intake" (said at 0:13:29)

The speaker accurately describes established physiological responses to ketogenic diets. Restricting carbohydrate intake lowers circulating glucose and insulin levels, prompting rapid depletion of glycogen stores and excretion of bound water (along with natriuresis), resulting in immediate early weight loss. Furthermore, systematic reviews and controlled ad libitum feeding trials demonstrate that ketogenic states suppress appetite and hunger, leading individuals to spontaneously reduce their caloric intake.

0:16:20Andrew Koutniksupportedmoderate

Patients with type 1 diabetes have a life expectancy reduced by 10 to 20 years and have a tenfold higher risk of cardiovascular disease.

"you're supposed to live 10 to 20 years shorter, you're supposed to get at least one chronic complication of typically retinopathy of the eyes, neuropathy of the nerves, nephropathy of the kidneys, or you have tenfold higher risk of cardiovascular disease." (said at 0:16:20)

Large nationwide registry studies confirm that individuals with type 1 diabetes face a substantial reduction in life expectancy and elevated risk of microvascular and macrovascular complications. A population-based study in Scotland found that at age 20, individuals with type 1 diabetes experienced an estimated loss of life expectancy of 11.1 years for men and 12.9 years for women compared to the general population, with ischemic heart disease and microvascular end-stage organ damage driving much of the excess mortality. Cardiovascular disease risk is markedly elevated in type 1 diabetes compared to matched controls, particularly in early-onset disease.

0:23:38Andrew Koutniksupportedvery low

In 1796, physician John Rollo reversed type 2 diabetes in two patients by lowering carbohydrates.

"in 1796, John Rollo was a physician who applied these tools in type 2 diabetes to reverse two patients with type 2 diabetes condition with lowering carbohydrates." (said at 0:23:38)

Historical medical literature documents that in late 1796, British military physician John Rollo successfully treated diabetes mellitus in two patients (most notably Captain Meredith) by placing them on an animal-based diet that strictly restricted carbohydrates and vegetable matter, leading to the resolution of glycosuria and symptoms. While modern distinctions between type 1 and type 2 diabetes did not exist in the 18th century, medical historians recognize these patients as having what is now classified as non-insulin-dependent (type 2) diabetes. Because this historical evidence consists of an uncontrolled two-patient case series, the certainty of evidence is very low.

0:23:55Andrew Koutniksupportedmoderate

In the 1860s, William Banting resolved his obesity by self-administering a lower-carbohydrate dietary approach.

"We know that in 1860s that there was William Banting who actually went on to self-administer a lower carbohydrate approach and was able to resolve all of his own obesity." (said at 0:23:55)

The historical record confirms that in the 1860s, William Banting effectively resolved his obesity by following a dietary regimen that restricted carbohydrates (specifically sugars and farinaceous/starchy foods) under the guidance of Dr. William Harvey, which Banting documented in his widely published 1863 pamphlet 'Letter on Corpulence, Addressed to the Public'. Modern medical and nutritional literature widely acknowledges Banting's 1863 case as the first popular low-carbohydrate diet for obesity management.

0:24:38Andrew Koutniksupportedhigh

The ketogenic diet has been utilized clinically for over a century to reduce the frequency and severity of epileptic seizures.

"We've known for over 100 years that it's been applied to reduce the frequency and severity of seizures and epilepsy." (said at 0:24:38)

The claim is accurate. Dr. Russell Wilder at the Mayo Clinic first proposed and clinically introduced the ketogenic diet to treat epilepsy in 1921—over 100 years ago—to mimic the anti-seizure effects of fasting. Clinical studies throughout the 1920s documented its application in hundreds of patients, and contemporary systematic reviews confirm that ketogenic diets effectively reduce seizure frequency in individuals with drug-resistant epilepsy.

0:32:40Andrew Koutniksupportedhigh

Diabetic ketoacidosis is characterized by high glucose levels, deficient or near complete absence of insulin, and unregulated ketone levels that can exceed 10 millimolar.

"When someone's in diabetic ketoacidosis, there is high glucose levels, deficient or near complete absence of insulin, and unregulated ketone levels, sometimes north of 10 millimolar per liter." (said at 0:32:40)

Diabetic ketoacidosis (DKA) is characterized by severe relative or absolute insulin deficiency, marked hyperglycemia (conventionally defined as blood glucose >250 mg/dL), and excessive, uncontrolled hepatic ketogenesis leading to severe ketosis and metabolic acidosis. Clinical evaluations and diagnostic thresholds establish that circulating ketone concentrations (notably beta-hydroxybutyrate and acetoacetate) are markedly elevated in DKA, frequently reaching and exceeding levels around 8 to 10 mmol/L or higher.

0:33:15Andrew Koutniksupportedmoderate

In nutritional ketosis, glucose and insulin are maintained at regulated levels with ketones typically ranging from 0.3 to around 5 millimolar.

"in nutritional ketosis, in the context of diabetes or not, it is normal and regulated glucose levels, low but still present insulin. So, it's not an absence of insulin like in DKA, it's just a lower level of insulin that keeps glucose and ketones in regulated levels. And ketone levels range anywhere, I would actually change that barometer from 0.3 millimoles per liter upwards of a rough estimate around 5 millimolar." (said at 0:33:15)

The speaker's definition of nutritional ketosis matches established clinical and metabolic definitions. In nutritional ketosis, basal insulin levels remain low but sufficient to prevent the runaway lipolysis and severe metabolic derailment seen in diabetic ketoacidosis (DKA). Consequently, blood glucose remains regulated via gluconeogenesis, while blood beta-hydroxybutyrate (BOHB) levels rise from baseline (~0.1 mM) into a physiological, therapeutic range typically spanning from ~0.3–0.5 mM up to approximately 3.0–5.0 mM.

0:37:31Andrew Koutniksupportedmoderate

Individuals on high-carbohydrate diets almost never have blood beta-hydroxybutyrate levels above 0.3 millimolar.

"when you look at studies where people are on higher carbohydrate approaches, there's almost a complete they're almost never above 0.3 millimolar." (said at 0:37:31)

Published nutritional and metabolic studies demonstrate that individuals consuming standard or high-carbohydrate diets maintain baseline and postprandial blood beta-hydroxybutyrate (βHB) concentrations well below 0.3 mmol/L (typically ranging from <0.05 to 0.2 mmol/L). On high-carbohydrate diets, elevated postprandial insulin suppresses lipolysis and hepatic ketogenesis, preventing βHB from reaching threshold levels of nutritional ketosis (often defined as ≥0.5 mmol/L) or exceeding 0.3 mmol/L in the absence of extended fasting or prolonged strenuous exercise.

0:40:05Andrew Koutniksupportedmoderate

The brain metabolizes beta-hydroxybutyrate for energy in a dose-dependent manner based on circulating levels.

"we've known that since the 1960s that it can actually be utilized for brain energy metabolism. And it's utilized in for the by the brain in a dose-dependent manner, meaning the more that's present, the more your body is going to metabolize." (said at 0:40:05)

Human metabolic and kinetic studies confirm that cerebral uptake and subsequent oxidation (metabolism) of beta-hydroxybutyrate are directly and linearly related to circulating arterial ketone concentrations.

0:41:20Andrew Koutniksupportedmoderate

Beta-hydroxybutyrate directly blocks the NLRP3 inflammasome.

"There's also an anti-inflammatory properties where it has been shown to directly even block certain what they call inflammasomes. Inflammasomes, they know NLRP3 inflammasome is a great example." (said at 0:41:20)

Preclinical and in vitro research demonstrates that the ketone body β-hydroxybutyrate (BHB) specifically suppresses activation of the NLRP3 inflammasome. Mechanistic work in human monocytes and mouse models showed that BHB prevents potassium efflux and ASC oligomerization, blocking downstream caspase-1 activation and the production of pro-inflammatory cytokines IL-1β and IL-18, independently of its oxidation or GPR109A receptor signaling.

0:43:00Andrew Koutniksupportedmoderate

1,3-butanediol-based exogenous ketones elevate blood hydrogen ions, increase blood oxygen saturation (SpO2), and improve cognitive function in acute hypoxia.

"One of the effects of 1,3-butanediol based products... is that you have a slight change in the hydrogen ion levels within the blood. And that subtle elevation hydrogen ions in the blood seems to change the ability to uptake oxygen levels within through ventilation... and even in those extreme settings, we were seeing that you we increase SPO2, increase resilience against cognitive decline, and actually improve cognitive function against uh uh a placebo-controlled arm." (said at 0:43:00)

The speaker's description matches findings from randomized, placebo-controlled crossover trials evaluating (R)-3-hydroxybutyl (R)-3-hydroxybutyrate (a 1,3-butanediol-based ketone monoester) under acute hypoxic conditions. In a randomized crossover trial of 16 military personnel exposed to acute severe hypoxia (simulating 6,096 m / 9.7% O2) at rest, ingestion of the ketone monoester attenuated the decline in blood oxygen saturation (SpO2 was 76.8% vs. 70.4% in placebo, P = 0.049) and attenuated cognitive performance decline during the Defense Automated Neurobehavioral Assessment code substitution task (+6.8 correct responses/min compared to placebo, P = 0.018). While a companion study during exercise in hypoxia found that ketone monoesters attenuated SpO2 desaturation without a statistically significant cognitive benefit, the specific resting severe hypoxia trial demonstrates the SpO2 and cognitive improvements described.

0:48:50Andrew Koutniksupportedmoderate

Diets supplemented with medium-chain triglycerides (MCTs) work almost as effectively as standard ketogenic diets in managing epilepsy.

"there have been studies actually showing that MCT-based diets or uh natural forms of fat that convert to ketone bodies in epilepsy have also been shown to work almost as effectively as just ketogenic diets do uh in and of themselves." (said at 0:48:50)

Randomized controlled trial evidence demonstrates that medium-chain triglyceride (MCT) ketogenic diets have comparable efficacy to classical ketogenic diets for seizure control in intractable pediatric epilepsy. In a randomized clinical trial of 145 children (Neal et al., 2009), there were no statistically significant differences in seizure reduction or the proportion of patients achieving >50% or >90% seizure reduction between the classical and MCT-based diets at 3, 6, and 12 months. Systematic reviews and network meta-analyses also confirm similar overall efficacy across these dietary therapy variations.

0:55:45Andrew Koutniksupportedmoderate

Studies by Louise Burke and John Hawley found a 2% performance decline in elite race walkers on a low-carbohydrate diet lasting 5 days to 3 weeks.

"in 2017 to 2021, prominent researchers who do really, really rigorous research studied low carbohydrate intake—Louise Burke, John Hawley, and a few others—where they lowered carbohydrates in elite race walkers for 5 days to 3 weeks... And what they found is that while the athletes were transitioning into ketosis, they were already producing ketone bodies, but not fully transitioned by all measures, at least not confirmed, they saw a deterioration in performance, but only 2%." (said at 0:55:45)

A landmark 2017 study led by Louise Burke and John Hawley (part of the Supernova research series) investigated the effects of a 3-week ketogenic low-carbohydrate, high-fat (LCHF; <50 g/day carbohydrate) diet during intensified training in elite race walkers. The authors found that while high-carbohydrate groups improved their 10 km race walk times by 5.3% to 6.6%, the LCHF group experienced a 1.6% (approximately 2%) decline in performance (-1.6% [90% CI: -8.5%, 5.3%]) alongside impaired exercise economy (increased oxygen cost of movement).

0:57:15Andrew Koutniksupportedlow

Research by George Cahill in the 1960s showed that normalization of key brain energy metabolites during fasting or very low carbohydrate intake takes around 3 weeks.

"We have known since the 1960s, David, from George Cahill, that when individuals go on to these very low carbohydrate approaches, and the most extreme rapid form of that is a fast, that even we don't see a normalization of key brain energy metabolites until around after 3 weeks in duration." (said at 0:57:15)

Seminal metabolic research led by George Cahill and Oliver Owen in 1967 demonstrated that during prolonged starvation (several weeks), the human brain undergoes a major metabolic shift wherein ketone bodies (beta-hydroxybutyrate and acetoacetate) replace glucose as the primary fuel source. While this adaptation occurs progressively over several weeks of fasting to stabilize cerebral energy requirements, the original experimental catheterization data relied on a very small sample (3 obese patients undergoing 5 to 6 weeks of starvation).

0:59:15Andrew Koutniksupportedlow

Athletes keto-adapted for over 4 weeks performing at above 85% VO2 max derived the majority of fuel from fat, with fat oxidation rates exceeding 1.85 grams per minute.

"when we looked at what was fueling these athletes up to over 85% of their VO2 max, fat metabolism made up the majority of fuel substrate during this activity, and at a level of fat oxidation that was higher than any fat levels ever reported in the medical literature. Some athletes were over 1.85 grams of fat burned per minute during physical activity." (said at 0:59:15)

The statement describes findings from the FASTER (Fat Adapted Substrate oxidation in Trained Elite Runners) study by Volek and colleagues (PMID: 26892521). In this cross-sectional comparison of 20 elite ultra-endurance athletes, runners keto-adapted for an average of 20 months (range 9–36 months) exhibited a mean peak fat oxidation rate of 1.54 ± 0.18 g/min (compared to 0.67 ± 0.14 g/min in high-carbohydrate runners), with individual maximal fat oxidation rates in keto-adapted athletes reaching or exceeding 1.85 g/min. In these athletes, fat remained the predominant fuel source up to approximately 85% of VO2max, substantially shifting the metabolic crossover point seen in traditional high-carbohydrate athletes. The certainty of evidence is low due to the small cross-sectional observational design (n=20).

1:01:30Andrew Koutniksupportedmoderate

Ironman competitors on a 6-week ketogenic diet sustained 70% VO2 max cycling performance without deterioration compared to a high-carb diet despite experiencing higher rates of hypoglycemia.

"what we wanted them to do was sustain 70% of their VO2 max on a cycle bike for as long as they could before they fatigued below the 70% threshold... What we were finding is that when we compared the same athlete for 6 weeks on both of these diets... we found that yet again, athletes on the ketogenic diet did not see a deterioration in performance. But what was absolutely critical to this, David, is that the athletes on the ketogenic diet actually had a higher incidence of hypoglycemia. Yet, they maintained the equivalent level of physical performance." (said at 1:01:30)

A randomized crossover study in trained triathletes compared 6 weeks of a very-low-carbohydrate/ketogenic diet (40 g/day) versus a high-carbohydrate diet (380 g/day) during strenuous cycling time-to-exhaustion tests at 70% VO2 max. The trial found that time-to-exhaustion performance was maintained without deterioration on the ketogenic diet compared to the high-carbohydrate diet, while the low-carbohydrate condition resulted in lower glucose levels / exercise-induced hypoglycemia unless minimal carbohydrate supplementation was provided.

0:48:45Andrew Koutniksupportedmoderate

Medium-chain triglycerides were first clinically evaluated in the 1950s and 1960s as a therapeutic dietary intervention to promote weight gain in malnourished children.

"what's interesting about MCTs is they were the first quote-unquote exogenous ketone that had actually been studied for therapeutic use back in the 1950s and 60s for malnutrition disorders in children. So, kids that were undernourished or not able to grow sufficiently, they were actually given MCTs. The theory was that this was a way of overcoming some of the malnutrition issues that some of these children had in the gut. And it effectively worked. It increased body weight in these children" (said at 0:48:45)

Medium-chain triglycerides (MCTs) were introduced and evaluated clinically starting in the late 1950s and 1960s specifically for pediatric and adult patients suffering from gastrointestinal malabsorption syndromes, impaired lipid digestion, and associated malnutrition or failure to thrive. Because MCTs undergo rapid hydrolysis, do not strictly require bile salts or pancreatic micelle formation, and are transported directly via the portal vein rather than the lymphatic system, their administration successfully provided absorbable caloric energy and promoted weight gain in undernourished children with intestinal and lymphatic disorders.

1:06:11Andrew Koutniksupportedmoderate

Administering 10 grams of carbohydrates per hour during prolonged strenuous exercise improved endurance performance by 22% in both high-carbohydrate and ketogenic athletes.

"Well, when we gave 10 g per hour on both the high-carb diet and the low-carbohydrate ketogenic diet, both diets improved performance 22%." (said at 1:06:11)

A randomized crossover study in trained triathletes adapted to either a 6-week high-carbohydrate (380 g/day) or a very-low-carbohydrate/ketogenic (40 g/day) diet tested endurance capacity during a cycling time-to-exhaustion test at 70% VO2max. Administering a low dose of carbohydrates (10 g/h) during exercise prevented exercise-induced hypoglycemia and increased time to exhaustion by exactly 22% across both the high-carbohydrate and ketogenic diet conditions.

1:10:13Andrew Koutniksupportedmoderate

An average-weight male can store roughly 500 grams of carbohydrates (up to 2,000 kcal) as muscle glycogen, whereas females store approximately 300 grams.

"The average body weight male can probably hold somewhere between 500 g of carbohydrates, that's up to 2,000 calories in the form of muscle glycogen, females around 300 or so, obviously a little bit more than that if you're well trained." (said at 1:10:13)

Human metabolic balance and physiological studies show that skeletal muscle glycogen stores in average-sized, healthy adult males typically hold around 400 to 500 grams of carbohydrates (yielding roughly 1,600 to 2,000 kcal, calculated at 4 kcal/g), while females store proportionately less (around 300 to 400 grams) due primarily to differences in average body mass and skeletal muscle mass. Classical overfeeding and glycogen-loading studies demonstrate that glycogen storage capacity is approximately 15 g/kg of body weight and can accommodate an expansion of ~500 g.

1:14:03Andrew Koutniksupportedmoderate

Studies published in JAMA in 1924 and 1925 by Gordon and Levine showed that low blood glucose caused glycopenia and early onset fatigue in Boston Marathon runners.

"despite us knowing since the 1920s that low blood glucose levels from Harvard physicians in JAMA 1924, 1925, Gordon and Levine, you can look this up in JAMA, have shown that low blood glucose caused glycopenia and early onset fatigue." (said at 1:14:03)

The speaker accurately describes landmark historical research conducted on Boston Marathon runners by Harvard physicians Burgess Gordon, Samuel A. Levine, and colleagues, published in JAMA in 1924 and 1925. In the 1924 study (JAMA 82:1778–1779), post-race blood samples from runners demonstrated that profound exhaustion and collapse correlated with severe hypoglycemia (low blood glucose). In their follow-up 1925 study (JAMA 85:508–509), supplying runners with carbohydrates before and during the race prevented hypoglycemia, markedly reduced physical exhaustion, and improved finish conditions. This classic work established the role of blood glucose maintenance and carbohydrate availability in preventing fatigue during prolonged endurance exercise, a concept substantiated across a century of exercise metabolism research.

1:17:32Andrew Koutniksupportedlow

An analysis of 34 countries led by Duke researchers showed that 90% of the obesity epidemic can be explained by diet alone rather than lack of physical activity.

"In fact, a major analysis from 34 different countries from Duke and other investigative researchers all over the world including China actually showed that 90% of the obesity epidemic could be explained by diet alone and the remaining wasn't necessarily a lack of physical activity, but just alterations across individuals in energy expenditure." (said at 1:17:32)

A 2025 global analysis led by Duke University researchers (using the IAEA Doubly Labelled Water database) analyzed 4,213 adults across 34 populations worldwide. The study found that variations in body size-adjusted total energy expenditure accounted for only approximately one-tenth (~10%) of the increase in body fat percentage and BMI associated with economic development. In contrast, higher energy intake (particularly ultra-processed food consumption) accounted for the remaining ~90%, demonstrating that excess caloric intake rather than reduced physical activity is the primary driver of development-related obesity. The GRADE certainty is rated low due to the observational and cross-sectional nature of the data.

1:18:25Andrew Koutniksupportedmoderate

Nine out of ten American adults (90%) have suboptimal metabolic health as defined by elevated fasting blood glucose, high triglycerides, elevated waist circumference, or related biomarkers.

"nine out of 10 individuals have sub-optimal metabolic health as defined by a fasting blood glucose level that's elevated high triglycerides, elevated waistline, or some other metabolic biomarker that 9 out of 10 Americans are clearly showing adverse metabolic changes in those biomarkers." (said at 1:18:25)

A nationally representative cross-sectional study of US adults in the National Health and Nutrition Examination Survey (NHANES 2009–2016, n = 8,721) evaluated metabolic health across five key cardiometabolic biomarkers: waist circumference, fasting blood glucose/HbA1c, blood pressure, triglycerides, and HDL cholesterol, in the absence of related medications. Only 12.2% of US adults met the criteria for optimal metabolic health, meaning approximately 87.8% (nearly 9 out of 10) had suboptimal metabolic health across one or more of these parameters.

1:21:57David Perlmutter (host)supportedhigh

Alzheimer's disease currently affects approximately 6 million Americans.

"Yeah, it's affecting uh 6 million Americans currently." (said at 1:21:57)

The claim is supported by epidemiological surveillance and national reports. According to the Alzheimer's Association Facts and Figures reports, an estimated 6.2 to 6.5 million Americans aged 65 and older are living with Alzheimer's dementia in the United States.

1:10:47Andrew Koutniksupportedvery low

There are medical case reports of individuals weighing over 400 pounds who fasted for over a year.

"There's examples of individuals north of 400 lb that have fasted for over a year." (said at 1:10:47)

A well-documented medical case report published in 1973 describes a 27-year-old male weighing 456 lb (207 kg) who underwent medically supervised therapeutic starvation for 382 days (over a year), consuming only water, non-caloric fluids, vitamin, and mineral supplements. As a single case report, the evidence design is uncontrolled and rated as very low certainty regarding the safety or generalizability of prolonged therapeutic starvation.

1:11:34Andrew Koutniksupportedhigh

Adipose tissue is highly sensitive to insulin, such that subtle amounts of insulin dramatically blunt fat breakdown and lipolysis.

"The fat binds insulin at very high potency, meaning you need very little amounts of insulin at the fat to actually shut down fat metabolism. Not completely, but largely, okay? You dramatically blunt fat breakdown with just subtle amounts of insulin." (said at 1:11:34)

The claim is supported by established clinical and physiological evidence. Adipose tissue is exceptionally sensitive to the antilipolytic action of insulin. Classic hyperinsulinemic-euglycemic clamp and microdialysis studies in humans show that the half-maximal inhibitory concentration (EC50/IC50) of insulin required to suppress lipolysis and free fatty acid release is very low (roughly 10–15 μU/mL or ~50–70 pmol/L), which is near or slightly above basal fasting levels. Consequently, subtle physiological increments in circulating insulin dramatically blunt lipolysis and fat breakdown long before reaching the concentrations required to stimulate maximal peripheral glucose disposal.

1:16:22David Perlmutter (host)supportedlow

Fructose consumption reduces mitochondrial activity and energy expenditure while promoting fat storage through a mechanism mediated by increased uric acid.

"when we do consume sugar in the form of fructose something very similar happens in terms of locking up our fat uh and reducing energy expenditure, reducing mitochondrial activity such that we can build body fat, maintain body fat, and you know, certainly not what we want to do now, but that's through the mechanism of increased uric acid." (said at 1:16:22)

The speaker accurately describes the 'fructose survival hypothesis' proposed in the metabolic literature (particularly by Richard Johnson and colleagues). According to this mechanistic framework, fructose metabolism triggers rapid ATP depletion, activating AMP deaminase and generating intracellular uric acid. Uric acid induces mitochondrial oxidative stress, suppressing mitochondrial oxidative phosphorylation and aconitase activity in the Krebs cycle, which shunts substrate toward de novo lipogenesis and fat accumulation while decreasing cellular energy expenditure. While this pathway is well-characterized in vitro and in animal models, evidence establishing the magnitude and clinical significance of this specific uric-acid-dependent mechanism on whole-body energy expenditure in humans remains primarily hypothesis-generating.

3

Corroborated by web sources

0:28:40Andrew Koutnikcorroborated (web)

William Sansum was the first person in the United States to chemically extract and administer insulin to save a patient's life.

"So, William Sansum, where I used to work, was actually the first person in the United States of America to both chemically extract and also administer insulin to save the life of a patient in the United States of America." (said at 0:28:40)

No published record matching the claim that William Sansum was the first person in the United States to chemically extract and administer insulin to save a patient's life was located; this does not prove the claim false.

corroborated by web sources

Historical and medical sources confirm that Dr. William Sansum was the first physician in the United States to successfully extract insulin in a laboratory and administer it to a patient, treating Charles Cowan on May 31, 1922.

sansum.orgphilanthropyroundtable.org

0:29:00Andrew Koutnikcorroborated (web)

In 1925, William Sansum published a paper in JAMA advocating that patients receiving insulin should have enhanced dietary freedom, without support from randomized controlled trials.

"William Sansum the founder of the institute I worked at also published a paper in JAMA in 1925 where he then argued that patients with the ability to administer insulin should now have enhanced freedom in their dietary choices. He made this recommendation in the absence of any serious, rigorous, randomized control trial evidence." (said at 0:29:00)

No published record matching William Sansum's 1925 JAMA paper on enhanced dietary freedom for insulin-treated patients was located; this does not prove the claim false.

corroborated by web sources

Dr. William D. Sansum and colleagues published a landmark paper in JAMA (January 1926, detailing clinical work from 1925) advocating for more liberal carbohydrate diets in insulin-treated patients. As randomized controlled trials had not yet been introduced to medical research, his recommendations were based on observational clinical case series.

semanticscholar.orgmasteringdiabetes.org

0:50:20Andrew Koutnikcorroborated (web)

In 1962, MIT studied 1,3-butanediol for aerospace transport as a shelf-stable, high-caloric-density nutrient.

"So, then in 1962, MIT actually studied 1,3-butanediol, which is in products like Ketone-IQ, for aerospace transport. Why were they interested in that? Because it was a very shelf-stable molecule that could go into outer space with high caloric density." (said at 0:50:20)

No published record matching the claim that MIT studied 1,3-butanediol in 1962 as a shelf-stable, high-caloric-density nutrient for aerospace transport was located; this does not prove the claim false.

corroborated by web sources

In the early 1960s, researchers at the Massachusetts Institute of Technology investigated synthetic energy sources for extended human spaceflight, identifying 1,3-butanediol as a promising shelf-stable, high-caloric-density nutrient.

nih.gov

6

No source found (not proven false)

0:15:40Andrew Koutnikunverifiedvery low

Ninety-nine percent of patients diagnosed with type 1 diabetes never achieve normal metabolic control after diagnosis.

"where 99% of patients will never get normal metabolic control after their initial diagnosis." (said at 0:15:40)

No published record matching the claim that 99% of patients diagnosed with type 1 diabetes never achieve normal metabolic control after diagnosis was located; this does not prove the claim false.

0:30:10Andrew Koutnikunverifiedvery low

There are four times more published studies on pharmacological and technological diabetes advancements than on nutrition-based diabetes interventions.

"And they're fourfold higher more publications in just pharmacological and technological advancements than there is in nutrition." (said at 0:30:10)

No published record matching the claim that there are four times (or fourfold) more publications on pharmacological and technological diabetes advancements than on nutrition-based diabetes interventions was located; this does not prove the claim false.

0:29:40Andrew Koutnikunverifiedvery low

The American Diabetes Association issued its first nutritional guidance in the 1970s, modeling it on the inaugural U.S. Dietary Guidelines.

"And the American Diabetes Association in 1970s for the first time came out with their first nutritional guidance. And essentially what they did is they modeled the US dietary guidelines that first came out in the 1970s." (said at 0:29:40)

No published record matching the claim that the American Diabetes Association issued its first nutritional guidance in the 1970s modeled on the inaugural U.S. Dietary Guidelines was located; this does not prove the claim false.

0:58:45Andrew Koutnikunverifiedvery low

High-intensity athletic performance (6x800m sprints and 1-mile time trials above 85% VO2 max) did not deteriorate after 4 or more weeks on a ketogenic diet compared to a high-carbohydrate diet.

"what we found is that when athletes were either on a ketogenic diet or on a high-carb diet doing 6 by 800-meter sprints or a max-effort 1-mile time trial—so the fastest you can run for 4 to 6 minutes in duration—we found that the ketogenic diet did not produce any deterioration in physical performance in these high-intensity athletic endeavors." (said at 0:58:45)

No published record matching the specific study described (evaluating 6x800m sprints and a 1-mile time trial following 4 or more weeks of a ketogenic diet versus a high-carbohydrate diet) was located; this does not prove the claim false. Published randomized trials by the speaker and colleagues have evaluated acute meal-timing effects on 5k and 10k running, but peer-reviewed findings for this specific multi-week sprint and 1-mile interval intervention protocol have not appeared in the indexed literature.

1:06:45Andrew Koutnikunverifiedvery low

In a review of over 160 sports nutrition studies published in Endocrine Reviews, when carbohydrate feeding reliably improved performance, the placebo/control group experienced a precipitous drop in blood glucose levels 88% of the time.

"And what we found is that when we looked at these 160 different studies, when carbohydrates reliably improved performance, David, what was happening is that the placebo group of those studies, 88% of the time, the placebo or control group was seeing a precipitous drop in blood glucose levels." (said at 1:06:45)

No published record matching a review of over 160 sports nutrition studies in Endocrine Reviews reporting that placebo/control groups experienced a precipitous drop in blood glucose levels 88% of the time when carbohydrate feeding improved performance was located; this does not prove the claim false.

1:03:03Andrew Koutnikunverifiedvery low

Total circulating brain energy metabolites in the blood—including glucose, ketones, and lactate—are equivalent between high-carbohydrate adapted and ketogenic adapted endurance athletes.

"in the blood, not just glucose, but also ketones and lactate, all fuels for the brain, the high carbohydrate athletes and the ketogenic athletes had the same amount of brain energy metabolites circulating in the blood." (said at 1:03:03)

No published record matching the claim that total circulating brain energy metabolites (glucose, ketones, and lactate combined) are equivalent between high-carbohydrate adapted and ketogenic adapted endurance athletes was located; this does not prove the claim false.

Unverified means no publication matching the claim was located; it does not prove the claim false. Spotted an error? See the corrections policy - disputes from the people quoted are prioritized.