People that eat a 'paleo' diet operate under the idea that we should be eating more like our ancestors, and that metabolic diseases like diabetes and obesity are related to a mismatch between the foods our bodies should eat, and what we actually consume. The 'mismatch hypothesis' suggests that our bodies evolved to digest certain foods, and when humans eat foods that are radically different from those we're evolved for, health problems will occur as they fail to metabolize these foods.
This mismatch concept is not a new one, but it is difficult to test scientifically. Comparing groups of people that eat Western diets with those that eat more traditional ones usually also means trying to compare people that have different habits, histories, environments, and physiological characteristics. New research reported in Science Advances has attempted to test the hypothesis by investigating the same population of people in northwest Africa called the Turkana.
In the 1980s, the region the Turkana lived in was transformed dramatically by a major drought and the discovery of oil. Some people stopped their nomadic lifestyle and moved to villages, and others to cities where they began to consume processed foods that were high in carbohydrates. Some Turkana, however, continued to live in rural areas and rely on livestock like sheep, cattle, goats, and donkeys.
"We realized that we had the opportunity to study the effect of transitioning away from a traditional lifestyle, relying on almost 80 percent animal byproducts -- a diet extremely protein-rich and rich in fats, with very little to no carbohydrates -- to a mostly carbohydrate diet," said study co-author Julien Ayroles, an assistant professor of ecology and evolutionary biology at the Lewis-Sigler Institute for Integrative Genomics (LSI). "This presented an unprecedented opportunity: genetically homogenous populations whose diets stretch across a lifestyle gradient from relatively 'matched' to extremely 'mismatched' with their recent evolutionary history."
Increasing globalization has caused a similar shift in lifestyles around the world.
"Humans evolved in a very different environment than the one we're currently living in," said first study author Amanda Lea, a postdoctoral research fellow in the LSI.
In this study, Lea, Ayroles, and a research team based at the Mpala Research Center in Kenya and led by Dino Martins interviewed 1,226 Turkana living in 44 places, and collected their health data.
"This is a very important first paper from the Turkana genomics work and the Mpala NSF Genomics and Stable Isotopes Lab," said Martins. "Doing research like this study involves a huge amount of trust and respect with our local communities and with more remote communities: how we access them, how we interact. And the reason Mpala and Turkana can be a hub for this is because we have a long-term relationship. What has happened in many parts of the world where some of this research has been done, and it's gone wrong, is when you have researchers parachuting in and out of communities. That does not make people trust you -- it just creates a lot of anxiety and problems. But here, the communities know us. We've been there for 25 years. Our research staff are drawn from local communities."
Ten biomarkers of health were all found to be excellent in the Turkana who were continuing their traditional, rural lifestyle, as well as Turkana who did well raising livestock for trade or making and selling goods in villages. Conversely, there were more health problems in Turkana who had become city-dwellers, like higher rates of diabetes, cardiovascular illness, high blood pressure, and obesity. The longer a Turkana spent living in a city, the worse their health was; life-long city dwellers had the biggest risk of cardiovascular disease.
"We are finding more or less what we expected," said Ayroles. "Transitioning to this carbohydrate-based diet makes people sick."
"There's a cumulative effect," added Lea. "The more you experience the urban environment -- the evolutionarily mismatched environment -- the worse it's going to be for your health."
This study has not shown that protein-based diets are healthier, cautioned Ayroles. "One of the most remarkable things about the Turkana is that if you and I went on the Turkana diet, we would get sick really quickly!" he noted. "The key to metabolic health may be to align our diet and activity levels with that of our ancestors, but we still need to determine which components matter most."
The investigators have taken more surveys and are collecting more data; they want to expand this work to include more indigenous groups that are changing their lifestyles.
"We can learn so much about evolution and human health from the many traditional and subsistence-level populations around the globe," said Lea. "They are experiencing this extraordinary, rapid environmental change, and we can witness it in real-time."