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If your ancestors lived on a diet of fish, eggs and meat, you are likely to develop problems like obesity, diabetes and heart disease on daily meals comprising mostly carbohydrates. Researchers call this the “mismatch hypothesis”—that is, a mismatch between your diet and what your body has evolved to digest and process.
Now, researchers at the Lewis-Sigler Institute for Integrative Genomics (LSI), Princeton University, and the Mpala NSF Genomics and Stable Isotopes Lab in Kenya say they have found the perfect example to prove the mismatch hypothesis: the Turkana people from a desert in northwest Kenya.
Forty years ago, a drought forced a subset of Turkana nomads to settle down in villages and cities while many others stuck to their old nomadic ways—rearing cattle such as dromedary camels, zebu cattle, fat-tailed sheep, goats and donkeys, and getting 80% of their energy from animal products.
Those who settled down saw a “sudden and massive” change in their diet, as they started consuming more carbs and processed foods.
The researchers interviewed 1,226 Turkana adults across 44 locations and found that those who had moved to the city—and away from a diet rich in proteins and fats to one based mostly on carbohydrates—had more complaints of heart problems, obesity and metabolic problems like diabetes. Further, the longer the participants had been in a city or village, the worse their cardio-metabolic health seemed to be.
Why is this study important?
For one, it compares like and like: Turkana people with Turkana people, rather than people of a different ethnicity (we know that ethnicity plays a big role in the development of chronic conditions; for example, Asians and African-Americans are at higher risk for heart problems than Caucasians).
Julien Ayroles, assistant professor at LSI and senior researcher on the paper, said that the movement of Turkana people from a nomadic existence to villages and cities in 1980 "presented an unprecedented opportunity: genetically homogenous populations whose diets stretch across a lifestyle gradient from relatively 'matched' (animal products-based) to extremely 'mismatched' (carbohydrates-heavy) with their recent evolutionary history."
Second, the clear break between the two groups 40 years ago helped the scientists see how a change in the diet affects health—normally, this change occurs in a more dispersed manner in various settings, communities and countries.
To be sure, there are other factors to consider—other plausible causes of poorer health in the set that settled down in villages and cities. For example, a nomadic life might involve more exercise and less exposure to air pollution.
But the researchers were clear in what their findings indicate: "We are finding more or less what we expected… Transitioning to this carbohydrate-based diet makes people sick," Julien Ayroles said.
The researchers published their findings in Science Advances on 21 October, in a paper titled "Urbanization and market integration have strong, nonlinear effects on cardiometabolic health in the Turkana". Princeton University's Dean for Research Innovations Funds and the Mpala funds, among others, supported the research project and the researchers.
