Twenty-four-hour Fasting And Carbohydrate Restriction Alter Postprandial Glucose And Lipid Responses In Healthy Adults

PURPOSE: Prolonged fasting reduces carbohydrate (CHO) availability and oxidation. The metabolic response to feeding independently modulates cardiometabolic risk, but research has yet to examine the effects of 24-hour fasting and low CHO intake without energy restriction on postprandial glucose and triglyceride metabolism. METHODS: In a randomized crossover design, 16 healthy adults (13 men, BMI 24.8 ± 3.3 kg/m2, age 22 ± 4 years, mean ± SD) completed three 24-hour dietary conditions in counterbalanced order: i) fasting (0 g CHO); ii) CHO restriction without energy restriction (≤20 g CHO); iii) control diet without energy restriction (>150 g CHO). The next day, participants consumed a mixed-macronutrient liquid meal standardized to 1/3 of resting metabolic requirements, with blood samples collected throughout a 120 min postprandial period. RESULTS: Triglyceride responses diverged between conditions (time x condition, p = 0.012) and were decreased after fasting (tAUC 88.1 ± 27.9 mmol/L*120 min, p = 0.009) and CHO restriction (99.6 ± 12.1 mmol/L*120 min, p = 0.006) relative to control (115.1 ± 49.2 mmol/L*120 min). Glycemic responses were elevated after fasting (iAUC 148.7 ± 146.0 mmol/L*120 min) compared to control (55.8 ± 46.3 mmol/L*120 min, p = 0.009) and CHO restriction (81.4 ± 81.5 mmol/L*120 min, p = 0.014). There were no differences in the magnitude of insulin response between conditions. Baseline non-esterified fatty acid concentrations were highest after fasting (0.82 ± 0.34 mmol/L vs CHO restriction, 0.55 ± 0.27 mmol/L, p = 0.029; vs control, 0.42 ± 0.20 mmol/L, p = 0.0006), whereas tAUC increased after fasting (39.84 ± 13.7 mmol/L*120 min, p = 0.018) and CHO restriction (36.56 ± 11.9 mmol/L*120 min, p = 0.037) compared to control (28.92 ± 12.6 mmol/L*120 min). CONCLUSION: Twenty-four hours of either fasting or CHO restriction reduce postprandial triglyceride responses, an effect previously observed only after longer durations of nutrient restriction. Unlike fasting, CHO restriction did not impair glucose tolerance. Supported by funding from Salus Optima and University of Bath.