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

## TL;DR

This study found that habitual diet influences how the body uses carbohydrates and adapts metabolically, with Kenyan participants showing better metabolic responses than U.S. participants.

## Contribution

The study provides empirical evidence linking habitual diet patterns to metabolic fuel utilization and flexibility in human populations.

## Key findings

- Kenyan participants had higher carbohydrate oxidation and better metabolic flexibility compared to U.S. participants.
- Dietary factors like fiber, starch, and added sugars significantly predicted metabolic responses to carbohydrate challenges.
- Slowly digestible carbohydrates improved metabolic flexibility more in Kenyan participants.

## Abstract

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.

We assessed metabolic fuel utilization using a portable breath CO2 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 (RERest) was calculated from the CO2 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 RERest/MF to carbohydrate challenges.

Kenyan participants had higher RERest 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 RERest; and for Model 2 (carbohydrate quality), total fiber (P = 0.026), starch (P = 0.001) and added sugars (P < 0.001) were predictive of RERest.

The Kenyan cohort consuming a diet of high carbohydrate quality and low in fat showed greater carbohydrate oxidation and improved MF.