Most people ascribe to the idea that obesity is connected to eating too much and moving too little. Most also believe the idea that cardiovascular disease, diabetes and other chronic illnesses stem from obesity. But what if there’s something else at work. The “mismatch hypothesis suggests exactly that.
According to the mismatch hypothesis, each human body is evolved and adapted to eat and process foods similar to those our ancestors ate. It also suggests that straying from that class of foods will lead those bodies to struggle to metabolize many “mismatched” foods. The result is obesity and chronic diseases like diabetes and heart diseases.
“Humans evolved in a very different environment than the one we’re currently living in,” said Amanda Lea, a postdoctoral research fellow in the Lewis-Sigler Institute for Integrative Genomics (LSI), and the first author on a study appearing in the current issue of the journal Science Advances. “No one diet is universally bad. It’s about the mismatch between your evolutionary history and what you’re currently eating.”
The idea of dietary mismatch isn’t new. Everyone has a phenotype, or a biochemical and genetic “signature,” if you will. This affects and is effected by everything we eat, breathe and come in contact with in some way. So if we are genetically linked to ancestors who were primarily vegetarian in their diets, our bodies might not be genetically predisposed to digest meat well. That’s a part of the theory, anyway.
The problem in proving whether the idea has merit, scientifically, is the methods previously used to try to prove that. It’s a challenge to directly produce useful evidence. Previous studies on the subject have compared hunter-gatherer populations with Western populations. This leads to issues with not just diet, but lifestyle and genetic differences.
There is one group of people who represent an excellent benchmark for this idea, according to the researchers at Princeton University. In a remote desert in Kenya, a subsistence-level, pastoralist group of people known as the Turkana lived a quiet lifestyle. At least they did. Then oil was discovered nearby in the 1980’s. Add an extreme drought to that and what followed was rapid change to the region.
While traditional Turkana still live a largely pastoral lifestyle, depending on livestock for food and livelihood, many abandoned that lifestyle to move into villages and cities. While pastoral Turkana eat a diet that includes goats, fat-tailed sheep and Zebu cattle, those in the villages and cities have adopted a diet including processed foods, higher in carbohydrates. The experience of the Turkana is one that has already occurred numerous times around the globe as the undeveloped, pastoral world slowly becomes the industrialized, developed world.
“We realized that we had the opportunity to study the effect of transitioning away from a traditional lifestyle, relying on almost 80% animal byproducts — a diet extremely protein-rich and rich in fats, with very little to no carbohydrates — to a mostly carbohydrate diet,” said Julien Ayroles, an assistant professor of ecology and evolutionary biology and LSI who is the senior researcher on the new paper. “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.”
To assess the situation and try to get an answer to their question, Ayroles and Lea joined a research team led by Dino Martins at the Mpala Research Center in Kenya. Known primarily for ecological research, the Mpala Center used its familiarity with the region, and the Turkana, to undertake new anthropological and sociological research, as well as research into genetics and genomics. Driving this expansion was a new NSF-funded genomics lab.
Using the Mpala resources, the researchers gathered health information from 1,226 Turkana adults across 44 different locations. Interviews with the Turkana helped them expand the utility of the information gathered.
“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 an anxiety and problems. But here, the communities know us. We’ve been there for 25 years. Our research staff are drawn from local communities.”
Aryoles and Martins were first connected during their time at Harvard University. Martins was based at the Turkana Basin Institute. Visiting Martins, Aryoles observed Turkana women carrying water in jars to their homes. According to Martins, this water would be shared with the Turkana in the women’s family and the pastoral communities. It might represent all the water they would have to drink for a week, Martins told Aryoles.
“Julian says, ‘That’s not possible. Nobody can survive on that little water,'” Martins recalled. “And so his scientist’s brain gets thinking, and he comes up with this project to say, ‘How is it that humans can survive in this incredibly harsh environment?’ And I turned it around by saying, ‘Actually, I think the question is, “How is it that we’ve adapted to survive in other environments?” Because of course, this is the environment that we all came out of.”
Using 10 biomarkers, the team expanded the project, reviewing and assessing health profiles of Turkana across the region. What they found was interesting, and may be a cautionary tale for development and health around the world, particularly as it relates to indigenous and pastoral populations and their health.
For the Turkana who continued to live their traditional, pastoral lifestyle, all 10 biomarkers were excellent. The same was true for those who had migrated to rural villages. Most of these raised livestock for trade or made and sold woven baskets or charcoal.
Those Turkana who had moved into cities, however, hadn’t fared as well. Their cardio-metabolic health had suffered significantly. This population displayed much higher levels of high blood pressure, cardiovascular disease, obesity and diabetes. The longer they had lived in cities, the worse their biomarkers were. Life-long city dwellers were universally at serious to severe risk of cardiovascular illness.
“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.”
Ayroles cautioned that the research should not be interpreted as favoring a protein-based diet. “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 said. “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 research continues with the Turkana. The researchers are looking to study other indigenous groups in similar situations. For example, many Pacific islander groups are experiencing similar adjustments as their lifestyles shift away from the traditional.
“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.”
Does a change in the kinds of foods we eat impact how our bodies metabolize food and deal with nutrients? Is evolution a driver of this metabolic change and it’s effects? Is the experience of the Turkana the same one other pastoral or primitive populations had when the world around them developed?
Can the lessons learned with the Turkana and other groups help us avoid the health fate that seems so integrally connected to development and “Westernization?” Is living in a developed world worth the toll it seems to take on humans as we move further from our “natural state?”
I’m not sure, but one thing seems certain. If we don’t find a way to make progress without destroying our health, that progress may not be worth the effort and sacrifice.
Keep the faith and keep after it!
Journal Reference – Amanda J. Lea, Dino Martins, Joseph Kamau, Michael Gurven, Julien F. Ayroles. Urbanization and market integration have strong, nonlinear effects on cardiometabolic health in the Turkana. Science Advances, 2020; 6 (43): eabb1430 DOI: 10.1126/sciadv.abb1430