Glycogen storage capacity and de novo lipogenesis during massive carbohydrate overfeeding in man.
Level 4 - case-series / case-control
Uncontrolled physiological metabolic balance study in a case series of 3 participants.
PubMed 3165600 · doi:10.1093/ajcn/48.2.240
What was done
Metabolic balance measurements were performed in three men to determine the fate of massive carbohydrate overfeeding. Participants first underwent glycogen depletion via 3 days of exercise and a low-carbohydrate, high-fat diet (decreasing from 1994 +/- 65 kcal/d to 1361 +/- 247 kcal/d; 15% protein, 75% fat, 10% carbohydrate). They then underwent 7 days of carbohydrate overfeeding (11% protein, 3% fat, 86% carbohydrate) starting at 3642 +/- 263 kcal/d and increasing progressively to 4930 +/- 311 kcal/d, followed by 2 days of carbohydrate restriction (602 kcal/d; 85% protein, 15% fat).
What was found
Glycogen storage capacity was approximately 15 g/kg body weight, accommodating a gain of approximately 500 g before net lipid synthesis contributed to fat mass. Following saturation of glycogen stores, massive carbohydrate intakes were disposed of via high carbohydrate-oxidation rates and substantial de novo lipid synthesis (150 g lipid/d utilizing approximately 475 g carbohydrate/d) without postabsorptive hyperglycemia.
Why it matters
This study provides physiological reference values for human glycogen storage capacity and demonstrates that substantial de novo lipogenesis from carbohydrate occurs only after glycogen stores are saturated.
Limits
The sample size was extremely small (n = 3) and restricted entirely to men. The dietary protocol involved extreme, non-habitual macronutrient compositions and caloric overfeeding, limiting generalizability to ordinary diets, women, or individuals with metabolic disease.
Cited by
- supports The human body stores approximately 2,000 calories of carbohydrate as glycogen, while fat tissue can store well in excess of 100,000 calories.