The “mismatch hypothesis” argues that our bodies evolved to digest foods our ancestors ate and that we will struggle to handle “unfamiliar” foods. In other words, no style of eating is universally bad; instead, what contributes to obesity and poor health is the mismatch between our evolutionary history and what we’re currently eating.

While this theory is hard to test directly, the Turkana—a pastoralist population in a remote section of Kenya—presents a natural experiment. Traditional Turkana still rely on livestock for subsistence, while Turkana who’ve relocated to cities have switched to diets that are much higher in carbohydrates and processed foods.

As reported in Science Advances, the effect of transitioning away from a traditional, “matched” diet, relying much more on protein and fat than carbohydrates, to an evolutionary, “mismatched” one that is much higher in processed carbs has not been good for the health of city-dwelling Turkana. They exhibit poorer cardiometabolic health with much higher levels of obesity, diabetes, cardiovascular illness and high blood pressure. The researchers found a cumulative effect—the more the Turkana experienced the urban environment and the mismatched style of eating, the worse it was for their health.

The key to better metabolic health for all of us may be to align our diet with that of our ancestors and our evolutionary history. Perhaps the future of personalized nutrition will help us determine which dietary components matter most. It’s likely that if you and I adopted the traditional Turkana diet, our bodies would cry foul.

See also: Can We Get All of Our Nutrients From Food?