Researchers compared how people from Kenya and the United States use food for energy based on what they typically eat. They found that Kenyans, who eat more whole grains and fiber and less fat, were better at switching between burning carbohydrates and other fuel sources. Americans, who eat more processed foods and added sugars, showed less flexibility in how their bodies use different types of fuel. This suggests that eating whole foods and fiber-rich carbohydrates might help your body become more efficient at using whatever fuel it needs.

The Quick Take

  • What they studied: Whether eating different types of diets affects how well your body can switch between burning carbohydrates and other fuels for energy
  • Who participated: 23 people from Kenya and 13 people from the United States with typical eating habits from their respective countries
  • Key finding: Kenyans showed better metabolic flexibility (ability to switch fuel sources) and burned more carbohydrates efficiently, likely because their diet contained more fiber, whole grains, and less added sugar and fat
  • What it means for you: Eating more whole grains, fiber, and less processed foods with added sugars may help your body become more efficient at using different types of fuel. However, this is a small study, so more research is needed before making major dietary changes based on these findings alone

The Research Details

This study compared two groups of people with very different eating habits. Kenyan participants typically ate traditional diets high in whole grains and fiber but low in fat. American participants ate typical Western diets with more processed foods, added sugars, and fat. Researchers gave each person two types of carbohydrate challenges: one with fast-digesting carbs (like white bread) and one with slow-digesting carbs (like whole grains). They measured how efficiently each person’s body burned these carbohydrates using a special device that measured carbon dioxide in breath.

The researchers collected detailed information about what each person normally ate using three separate 24-hour food recalls. They then used statistical analysis to see if the differences in diet explained the differences in how well people’s bodies could switch between burning different fuel sources. This approach allowed them to compare real-world eating patterns with actual metabolic responses.

Understanding how diet affects your body’s ability to use different fuels is important because metabolic flexibility—the ability to switch between burning carbs, fat, and other fuels—is linked to better overall health and weight management. By studying people with naturally different diets, researchers can see how real-world eating patterns influence this important metabolic ability without requiring people to follow strict experimental diets.

This study has both strengths and limitations. The strength is that it compares real people eating their normal diets rather than forcing everyone to eat the same experimental food. However, the sample size is quite small (only 36 people total), which means the results may not apply to everyone. The study is also observational, meaning researchers observed what people naturally ate rather than randomly assigning them to different diets, so we can’t be completely certain diet caused the differences observed.

What the Results Show

Kenyan participants showed significantly better metabolic flexibility compared to American participants, meaning their bodies were better at switching between burning carbohydrates and other fuels. This difference appeared regardless of whether they consumed fast-digesting or slow-digesting carbohydrates. Kenyans also burned more carbohydrates overall, suggesting their bodies were more efficient at using this fuel source.

When researchers looked at specific dietary components, they found that eating more total fiber, more starch (from whole grains), and less added sugar were all associated with better metabolic flexibility. The Kenyan diet, which naturally contained these characteristics, appeared to train the body to be more metabolically flexible. In contrast, the American diet pattern—higher in added sugars and fat but lower in fiber—was associated with reduced metabolic flexibility.

The study also measured how quickly food moved through the stomach (gastric emptying). While the paper mentions this measurement, the specific results for stomach emptying weren’t fully detailed in the abstract, suggesting this may have been a secondary outcome. The researchers used advanced statistical modeling to understand how different dietary components independently contributed to metabolic flexibility, beyond just comparing the two countries.

Animal studies have previously shown that diet affects how bodies use fuel, but this study is valuable because it demonstrates the same pattern in humans eating their normal diets. The findings align with previous research suggesting that high-fiber, whole-grain diets support better metabolic health. However, most previous studies have focused on weight loss or blood sugar control rather than specifically measuring metabolic flexibility, making this research a useful addition to our understanding.

The sample size is quite small—only 36 people total—which limits how much we can generalize these findings to larger populations. The study compares two very different populations (Kenya vs. US) with many differences beyond just diet, including genetics, physical activity levels, and climate, which could influence results. The study is observational rather than experimental, meaning we can see associations between diet and metabolic flexibility but cannot prove that diet directly causes the differences. Additionally, dietary data was collected using recall methods, which can be subject to memory errors and bias.

The Bottom Line

Based on this research, eating more fiber-rich whole grains, reducing added sugars, and moderating fat intake may help improve your body’s metabolic flexibility. However, confidence in this recommendation is moderate because the study is small and observational. These dietary changes are generally considered healthy for other reasons too (heart health, blood sugar control), so they’re worth trying. Consult with a healthcare provider or registered dietitian before making significant dietary changes, especially if you have existing health conditions.

This research is most relevant for people interested in optimizing their metabolic health, managing weight, or improving their body’s efficiency at using different fuel sources. It may be particularly interesting for people with metabolic concerns like prediabetes or metabolic syndrome. People eating typical Western diets high in processed foods may see the most benefit from dietary changes. However, these findings shouldn’t replace medical advice for people with diagnosed metabolic conditions.

Changes in metabolic flexibility likely develop gradually over weeks to months as your body adapts to a new diet. You probably won’t notice dramatic changes immediately, but consistent eating of whole grains, fiber, and less processed food should gradually improve your body’s ability to use different fuels. Most metabolic adaptations take 4-12 weeks to become noticeable.

Want to Apply This Research?

  • Track daily fiber intake (aim for 25-30g) and added sugar intake (aim for less than 25g for women, 36g for men) for 8-12 weeks. Monitor energy levels and hunger patterns as potential indicators of improving metabolic flexibility
  • Use the app to log whole grain servings, vegetables, and legumes at each meal while reducing processed foods and sugary drinks. Set a daily fiber target and track progress toward it
  • Create a weekly summary tracking fiber intake, added sugar intake, and subjective measures like energy levels and hunger satisfaction. Compare trends over 4-week periods to identify patterns and improvements in how you feel

This research suggests associations between diet patterns and metabolic flexibility but does not prove causation. Individual results may vary based on genetics, activity level, and other factors. People with diabetes, metabolic syndrome, or other medical conditions should consult their healthcare provider or registered dietitian before making significant dietary changes. This information is for educational purposes and should not replace professional medical advice.