Mark Hyman, MD · 2025-06-18 · Andy Galpin, Mark Hyman (host)
The Real Reason You're Always Tired Has Nothing to Do With Sleep
32 claims checked against research: 2 contradicted 1 contradicted online 8 overstated 3 needing context 12 supported 6 unverified
2 Contradicted by research
Monozygotic twin research shows that individuals who do not lift weights exhibit lower muscle quality and lose power and speed more frequently as they age.
"We've done this research in our lab with twins, right? So monozygous twins, exact same DNA with different things. And when you look at the folks who don't lift weights, they don't tend to have as high muscle quality. They start to lose power and speed more frequently." (said at 1:07:55)
The speaker claims that monozygotic twin research from their lab demonstrates that individuals who do not lift weights exhibit lower muscle quality and lose power and speed more frequently. However, the published monozygotic twin study from this research group evaluated 30 years of discordant chronic endurance training (not resistance training/weightlifting) in a single pair of identical twins. In that study, the endurance-trained twin actually exhibited lower muscle size and strength as well as poorer muscle quality compared to the untrained twin, alongside a shift toward slow-twitch (MHC I) muscle fibers. No published monozygotic twin study demonstrating lower muscle quality or accelerated power/speed loss specifically resulting from a lack of weightlifting was identified.
- contradicts: Muscle health and performance in monozygotic twins with 30 years of discordant exercise ha… (European journal of applied physiology 2018) · cited 57x in the literature
"TT exhibited: (1) lower body mass, body fat%, resting heart rate, blood pressure, cholesterol, triglycerides, and plasma glucose, (2) greater relative cycling power, anaerobic endurance, and aerobic capacity (VO 2 max), but lower muscle size/strength and poorer muscle quality, (3) more MHC I (slow-twitch) and fewer MHC IIa (fast-twitch) fibers" (abstract, results, passage verified)
pubmedfull study (doi)
Analysis of the NHANES database revealed no correlation between muscle mass and strength training history, indicating that higher muscle mass in that survey population was driven by higher total body mass.
"We looked in that database, and what's interesting is there was no relationship between the amount of muscle mass people had and their strength training history really in that database. You know what that tells us? How did they get their muscle? If they had a lot of muscle, that had we had no bearing or understanding if they lifted weights or not, which means people in those national databases have generally accrued their muscle by just being bigger, larger people, ate more, bigger body mass comes along with more muscle." (said at 1:26:00)
The assertion that NHANES data show no relationship between muscle mass and strength training history is contradicted by published analyses of the NHANES database. A cross-sectional study of 4,872 U.S. adults from NHANES (1999–2004) demonstrated that muscle-strengthening frequency was significantly and positively associated with fat-free mass percentage in both men and women after adjusting for age, height, race-ethnicity, education, and caloric intake (PMID: 27031912). While it is well-established that absolute fat-free mass in general population surveys scales strongly with total body mass and fat mass (PMID: 27862528), strength training history does correlate significantly with body composition measures in NHANES.
- contradicts: Combined Increases in Muscle-Strengthening Activity Frequency and Protein Intake Reveal Gr… (The Journal of frailty & aging 2015) · cited 6x in the literature
"One unit increase in MSF or protein intake (β-coefficient, ±E) was associated with significantly more FFM% in males (0.6±0.1%; 3.5±0.4%) and females (0.4±0.1%; 5.9±0.4%). Independent of protein intake, males and females with MSF=0 had mean ±SE FFM% of 74.4±0.4 and 60.7±0.3, respectively, while mean ±SE FFM% of males and females who met the recommendation of ≥2 times per week were 77.9±0.5 and 63.0±0.4." (abstract, results, passage verified)
pubmedfull study (doi) - context: Relationships among fat mass, fat-free mass and height in adults: A new method of statisti… (American journal of human biology : the official journal of the Human Biology Council 2017) · cited 4x in the literature
"The positive influence of fat mass (FM) on fat-free mass (FFM) has been quantified previously by various methods involving regression analysis of population data, but some are fundamentally flawed through neglect of the tendency of taller individuals to carry more fat." (abstract, background, passage verified)
pubmedfull study (doi)
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.