(OR17-01-26) Minimum Dietary Carbohydrate Requirement in Healthy Chinese Adults: A Controlled Feeding Trial Using Nutritional Ketosis as a Biomarker

Objectives: We aimed to assess 1) the minimum dietary carbohydrate requirement in apparently healthy Chinese adults by identifying the highest carbohydrate intake that avoids nutritional ketosis, 2) the effect modification by sex and age, and 3) validate a novel ex vivo method to monitor the 24-hour dynamics of β-hydroxybutyrate (BHB).

Methods: In this controlled feeding trial, 22 healthy adults (20–50 years) first completed a 3-day very-low-carbohydrate diet (20 g/d) to induce nutritional ketosis (fasting venous BHB ≥ 0.5 mmol/L). Carbohydrate intake was then progressively increased (40, 50, 70, 90, 110 g/d) while maintaining protein and fat intakes constant. We measured circulating BHB levels via gold-standard venous blood biochemistry and a novel ex vivo method for continuous ketone monitoring (CKM). Linear mixed-effects models were used to estimate the carbohydrate intake threshold corresponding to a BHB concentration of 0.5 mmol/L.

Results: During the study period, participants’ resting metabolic rate remained unchanged, although a shift from carbohydrate to fat oxidation was confirmed during ketosis. A significant negative nonlinear relationship was observed between carbohydrate intake and BHB levels. The minimum carbohydrate requirements were approximately 105 g/d for males and 93 g/d for females as indicated by venous blood measures, and 88 g/d for males and 78 g/d for females via CKM. There was strong agreement between the CKM and venous measurements (intraclass correlation coefficient [ICC] = 0.97).

Conclusions: Findings from this controlled feeding study provide sex-specific estimates of the minimum carbohydrate requirement in healthy adults and validated the clinical utility of a novel ex vivo method for dynamic metabolic monitoring.

Funding Sources: This work was supported by the National Key Research and Development Program of China and the Dietary Nutrition Research and Public Education Fund.