Role of habitual diet in metabolic fuel utilization and metabolic flexibility, evidence in Kenyan and U.S. cohorts

Background/objectives Animal studies support that diet affects metabolic fuel utilization and metabolic flexibility. We hypothesized that individuals with contrasting dietary patterns would have different metabolic responses. Differences in metabolic fuel utilization, metabolic flexibility, and gastric emptying time to carbohydrate challenges (rapidly vs slowly digestible carbohydrates [RDC/SDC]) were assessed between US and Kenyan cohorts consuming diets characteristic of each population. Subjects/methods We assessed metabolic fuel utilization using a portable breath CO 2 measuring device and gastric emptying in two cohorts (Kenya, n = 23; US, n = 13) for 2 h following RDC and SDC challenges. Study meals, matched in energy content (732 kJ), consisted of test carbohydrates (30 g) mixed into applesauce (200 g). An estimated respiratory exchange ratio (RER est ) was calculated from the CO 2 values. Metabolic flexibility (MF) was assessed using Percent Relative Cumulative Frequency followed by modeling with the Weibull Cumulative Distribution function. We collected dietary data using three 24-h dietary recalls and used multivariate mixed effect models to assess dietary influences on RER est /MF to carbohydrate challenges. Results Kenyan participants had higher RER est and greater MF compared to US participants regardless of the carbohydrate challenge ( P < 0.0001), and had improved MF response with SDC vs RDC. Multivariate Model 1 (macronutrient composition) showed that carbohydrate ( P = 0.02) and protein ( P < 0.001) were predictive of RER est ; and for Model 2 (carbohydrate quality), total fiber ( P = 0.026), starch ( P = 0.001) and added sugars ( P < 0.001) were predictive of RER est . Conclusion The Kenyan cohort consuming a diet of high carbohydrate quality and low in fat showed greater carbohydrate oxidation and improved MF.