Halfway up Mount Kilimanjaro in Tanzania, 2,500 meters above sea level, researchers set up a small pop-up restaurant that nearly washed away during the rainy season. Here, healthy young African men walk in for a meal three times a day. On the menu: dishes high in fat, meat and calories. All of this lavished with unlimited ketchup and mayonnaise.
These men are participating in a study led by internist-infectous diseases specialist Quirijn de Mast. In Tanzania, he is studying the factors that influence the immune system functions in healthy people. Nutrition plays an important role. Quirijn compares the diet of Tanzanians living in rural areas with Tanzanians living in cities. For the study in the pop-up restaurant, men who usually eat traditional Tanzanian food are temporarily given a "western" diet high in processed foods, sugar and fat. Conversely, men who live in cities are temporarily given a traditional Tanzanian diet. The researchers measure the effects of the two diets on the body.
Beer made from bananas
‘In our studies, we see clear differences in the function of the immune system and the composition of the bacteria in the gut between people who live in the city and those who live in the countryside,' says Quirijn. 'The traditional Tanzanian diet of rural people causes less inflammation and a healthier composition of bacteria and fungi in the gut as compared to a western diet. Many people think that we are given this so-called intestinal flora at birth, and that it remains stable. But the gut flora actually seems flexible and can change in a matter of weeks.'
Tanzanians in rural areas traditionally eat mainly plant-based foods high in fiber and fermented products. 'An important meal is ugali, a porridge made from corn or millet,' explains Godfrey Temba. Godfrey is from Tanzania and works as a PhD student in Quirijn's group. 'Tanzanians in rural areas eat a lot of spinach and other vegetables, whole grain cereals and different types of beans. Bananas are also often on the menu, and they even brew banana beer. They eat meat at most once a week.’
When Tanzanians move to the big cities, their diet changes. Godfrey: 'They come into contact with western products, fast food and a lot more meat. But it's not only what they eat that changes, but also how they prepare it. In the countryside, people cook the food, while in the cities they often switch to deep-frying. In addition, in the countryside they eat a lot of unprocessed grains, while in the city they buy more processed food, such as white rice without the husks. And that's exactly what contains the most healthy substances.’
‘The consequences of the changed lifestyle are huge. We are seeing a rapid increase in western diseases, particularly in the cities of Tanzania,' Quirijn explains. ‘In the past, infectious diseases, such as malaria, HIV and tuberculosis, were a major problem. Now, more and more lifestyle diseases are seen as well, such as type 2 diabetes, obesity, and cardiovascular diseases. Sticking to the traditional plant-based diet will hopefully slow down this development, because the health care system in Africa cannot cope with an epidemic of non-communicable diseases.’
How does a traditional Tanzanian diet protect against excessive inflammation? In a study published in Nature Immunology, Quirijn and Godfrey examined substances in the blood of Tanzanians in rural and urban areas. What did they find? In the countryside, people had higher concentrations of so-called flavonoids in their blood. Those concentrations changed with the seasons. Flavonoids are found widely in plants and they inhibit inflammation. And it is precisely inflammation that plays an important role in the development of numerous lifestyle diseases.
But intestinal flora can also play a role. In a follow-up study, published in Nature Communications, the researchers looked at the intestinal flora of Tanzanians in the countryside and in the city, and they also studied Dutch people. They saw major differences in the composition of the gut flora. Some bacteria in the gut make substances that are involved in inflammation. Tanzanians in rural areas had the fewest bacteria associated with inflammation, and the Dutch had the most. Tanzanians in big cities were in between, but closer to the Dutch.
The research in Tanzania also has value for us in the Netherlands. Quirijn: ‘Here, urbanization and the change in lifestyle took place quite some time ago. Our research in Tanzania is being conducted in a population that is right in the middle of this change, which is giving us new insights into the role of lifestyle on health. We are also studying which products or substances strengthen the immune system. Flavonoids already came out clearly, including apigenin. We want to know more about that. There has been a lot of attention in recent years on the importance of healthy food, certainly also in the Radboudumc. The immune system plays an important role in numerous disorders. As far as I'm concerned, in the future, we will work even more intensively on the question of how we can influence the immune system through nutrition.’
Traditional Tanzanian recipe (4 people): Ugali and mchicha (corn porridge and curry with spinach and peanuts)
500 grams maize flour
900 grams spinach (chopped)
2 tbsp peanut butter
2 tomatoes (in pieces)
1 red onion (chopped)
2-3 tablespoons curry powder
1 cup coconut milk
Pinch of salt
Freshly ground black pepper
Ugali: boil 1 liter of water, add the cornmeal while stirring. Boil for 10-15 min, stirring frequently. It should become firm. Add more water if necessary. Cut the ugali or make little balls.
Mchicha: mix peanut butter and coconut milk. Heat a skillet and fry the onion, tomatoes, salt and curry powder, until the onions are soft. Add the spinach and heat briefly. Add the coconut mixture and mix well. Heat until hot and add the pepper.
Who is Quirijn de Mast?
Quirijn de Mast works as an internist-infectious diseases specialist at the Department of Internal Medicine. What is he looking forward to for 2022? 'In 2022, Godfrey will receive his PhD and we will celebrate an anniversary: 25 years of collaboration between the Radboudumc and the university hospital in Tanzania, the Kilimanjaro Christian Medical Center (KCMC). Thanks to this intensive collaboration, we are able to do this great research. So many things to look forward to!'
The results described in this article are based on two major projects. The Human Functional Genomics Project is coordinated by colleagues Mihai Netea and Leo Joosten. The TransMic Project was funded by the European Union from the Horizon 2020 program.
The goal of the studies is to understand which factors influence the function of the immune system. The researchers are studying different groups, from a particular area or with a specific condition. In the TransMic Project, they are looking specifically at the role of nutrition and gut flora in people in Tanzania and Burkina Faso. In both projects, researchers analyze DNA, map the gut flora and measure markers in the blood. They also study how immune cells in the blood react to stimulation by pathogens. In this way, the researchers can compare health effects in large groups.
This article was previously published in Radbode #8 2021, and was based on the following two publications:
- Stražar, M. et al. (2021). Gut microbiome-mediated metabolism effects on immunity in rural and urban African populations. Nature Communications
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