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.
- contradicts: Glucose and Fructose Hydrogel Enhances Running Performance, Exogenous Carbohydrate Oxidati… (Medicine and science in sports and exercise 2022)
"Absolute and relative endogenous CHO oxidation was lower in both CHO conditions compared with placebo (P < 0.001), with no difference between CHO conditions. Absolute and relative liver glucose oxidation and muscle glycogen oxidation were not different between CHO conditions." (abstract, results, passage verified)
pubmedfull study (doi) - contradicts: Increased exogenous but unaltered endogenous carbohydrate oxidation with combined fructose… (European journal of applied physiology 2022)
"Exogenous carbohydrate oxidation rates were higher in the 120 g h -1 condition (120-180 min: 1.51 ± 0.22 g min -1 ) as compared to the 90 g h -1 condition (1.29 ± 0.16 g min -1 ; p = 0.026). Endogenous carbohydrate oxidation rates did not differ between conditions (2.15 ± 0.30 and 2.20 ± 0.33 g min -1 for 120 and 90 g h -1 conditions, respectively; p = 0.786)." (abstract, results, passage verified)
pubmedfull study (doi) - contradicts: From Metabolism to Medals: Contemporary Perspectives and Revisiting Carbohydrate Guideline… (The Journal of nutrition 2026)
"From a metabolic perspective, the ergogenic effect of CHO intake is likely mediated by liver (and potentially muscle) glycogen sparing, maintenance of plasma glucose concentrations, and whole-body CHO oxidation rates, such that the required exercise intensity can be sustained for a longer duration thereby delaying fatigue." (abstract, results, passage verified)
pubmedfull study (doi)