Ultra-processed foods are dominating much of what Americans eat. (Rimma Bondarenko/Shutterstock)
Study shows the shocking impact that processed foods have on the body — and how a traditional African diet could add more healthy years to your life.
In a nutshell
Just two weeks on a Western diet can trigger inflammation and weaken immune responses, even in healthy young adults. These changes may persist weeks after returning to a healthier diet.
Switching to a traditional African heritage diet rich in plant-based, minimally processed foods significantly reduced inflammation, supporting its protective role against chronic diseases.
A traditional fermented banana drink (Mbege) also showed anti-inflammatory effects, highlighting the potential health benefits of fermented foods often overlooked in modern diets.
NIJMEGEN, Netherlands — Two weeks of burgers and fries might do more damage than you think. A new study shows that men who switched from traditional African diets to Western foods for just 14 days experienced alarming increases in inflammation and immune dysfunction. The changes lingered for weeks after returning to their normal diets.
The study, published in Nature Medicine, demonstrates how quickly the body’s immune and metabolic systems respond to dietary shifts. Its findings raise concerns about the widespread abandonment of heritage diets in favor of processed Western foods.
The Experiment: Switching Diets in Tanzania
Researchers from Tanzania’s Kilimanjaro Christian Medical University College collaborated with scientists from Radboud University Medical Center in the Netherlands to conduct this dietary experiment. They worked with 77 healthy young men from northern Tanzania, some from rural areas who typically ate traditional Kilimanjaro diets and others from urban areas who consumed more Western-style foods.
For two weeks, the rural participants switched to a Western diet high in processed foods, while urban participants adopted a traditional heritage diet. A third group kept eating their usual Western diet but added daily consumption of Mbege, a traditional fermented banana beverage, for one week.
Western dietary habits include eating an abundance of processed foods. (Photo by Sander Dalhuisen on Unsplash)
The men who switched from their traditional diet to Western foods gained an average of about 5.7 pounds. Their blood tests showed increasing levels of inflammation markers and metabolic changes linked to disease risk. More concerning, their immune cells became less responsive to microbial challenges, essentially making their immune systems temporarily less effective.
Many of these negative changes persisted even four weeks after returning to their normal diets, indicating that even short periods of dietary changes might have lasting effects.
On the flip side, urban dwellers who temporarily switched to the traditional Kilimanjaro diet experienced mostly positive changes. Their blood showed decreasing levels of inflammatory proteins and beneficial metabolic shifts. Those who drank the fermented banana beverage also showed anti-inflammatory benefits.
What Makes These Diets Different?
The Kilimanjaro heritage diet typically includes green vegetables and legumes like kidney beans, plantains, cassava, taro, millet, and sorghum. These foods provide abundant fiber and plant compounds with known health benefits.
The Western diet featured foods like beef sausage, white bread with margarine, French fries, chicken stew with white rice, and processed maize porridge with added sugar.
The global nutrition transition happening as traditional diets give way to Western-style eating patterns is an important issue. While most nutrition research focuses on Western populations, this study examines how dietary changes affect people in sub-Saharan Africa, a region experiencing rising rates of chronic diseases like heart disease and diabetes.
At the genetic level, those eating the Western diet showed increased activity of genes related to inflammation and decreased activity of genes involved in immune function. Their blood samples also revealed changes in white blood cell counts and activation patterns indicating increased inflammation.
Traditional African diets are being steadily displaced by Western-style eating habits, driven by factors like urban growth, economic shifts, wider availability of processed foods, globalization, and evolving cultural norms.
Bottom Line: Diet Influences Inflammation
This rapid dietary shift occurring across developing regions might help explain the rising epidemic of noncommunicable diseases worldwide. Chronic inflammation, which can persist at low levels for years without obvious symptoms, damages tissues and organs over time. The study reveals how quickly inflammatory processes can be triggered by dietary changes, pointing to a potential mechanism for how Western diets increase disease risk.
What about the group that consumed the fermented beverage? After just one week of consuming Mbege, participants showed reduced inflammatory markers and increased production of anti-inflammatory compounds. This also supports growing research interest in fermented foods for gut health and immune regulation.
Mediterranean diets are a great alternative to Western diets because they have shown promising results for overall health.
(© fascinadora – stock.adobe.com)
For those living in Western countries, the results add more evidence that incorporating more elements from plant-rich, minimally processed dietary patterns might help reduce inflammatory burden. The Mediterranean diet, which shares many characteristics with the Kilimanjaro heritage diet (emphasis on plant foods, whole grains, limited processed foods), has similarly been linked to reduced inflammation and chronic disease risk.
Even short-term exposure to a Western diet can trigger inflammation that might increase disease risk over time. Traditional food systems face increasing pressure from globalization, but preserving valuable dietary traditions may help combat the rising global epidemic of chronic diseases.
Paper Summary
Methodology
The researchers set up a randomized controlled trial with 77 healthy men aged 20-40 years. They created three main groups: rural men who switched to a Western diet for two weeks, urban men who switched to a heritage diet for two weeks, and urban men who added a traditional fermented banana beverage to their Western diet for one week. Small control groups maintained their habitual diets throughout the study. All participants received freshly prepared meals three times daily at central locations. Blood samples were collected before the diet change, immediately after the intervention, and four weeks later as follow-up. These samples underwent comprehensive analysis for markers of inflammation, metabolic health, immune function, gene expression, and metabolite levels.
Results
The Western diet group gained an average of 5.7 pounds and showed increases in 26 inflammatory and cardiometabolic proteins in their blood. Their immune cells became less responsive to microbial challenges, suggesting impaired immune function. Genetic analysis revealed increased expression of inflammation-related genes and decreased expression of genes involved in adaptive immunity. The heritage diet group showed significant reductions in 28 inflammatory proteins and beneficial metabolic shifts without significant weight changes. The fermented beverage group showed anti-inflammatory effects, particularly increased production of anti-inflammatory compounds. Many changes persisted four weeks after the interventions ended, suggesting potentially lasting effects from even short-term dietary changes.
Limitations
The study had several constraints: participants ate as much as they wanted rather than receiving controlled portions, potentially confounding the results with weight gain in the Western diet group; only men participated due to cultural and logistical considerations; the sample size was relatively small (about 22 participants per group); the analytical methods for metabolite identification had some technical limitations; and the findings from the Chagga tribe’s diet may not apply equally to all traditional diets in the region. Despite these limitations, the results align with other research on diet and inflammation, strengthening the study’s conclusions.
Discussion and Takeaways
The research reveals how rapidly dietary changes can affect immune and metabolic systems, potentially influencing disease risk. The inflammatory responses observed with the Western diet help explain why urbanization and dietary westernization might increase chronic disease rates in populations undergoing nutrition transition. The anti-inflammatory effects of the heritage diet and fermented beverage suggest that preserving elements of traditional diets could help prevent chronic disease. For individuals in Western countries, incorporating more plant-rich, minimally processed foods might help reduce inflammation and disease risk. The findings add to growing evidence that traditional dietary patterns often promote better health than modern Western diets.
Funding and Disclosures
The study received support from the Joint Programming Initiative: A Healthy Diet for a Healthy Life and ZonMW (Netherlands), the Radboud Revolving Research Funds, the Spinoza Prize, a European Research Council Advanced Grant, and the German Research Foundation. The company AB Biotek provided funding for future studies to some researchers but had no involvement in this particular study’s design, execution, or publication.
Publication Information
The study “Immune and metabolic effects of African heritage diets versus Western diets in men: a randomized controlled trial” appeared in Nature Medicine on April 3, 2025. The research team included scientists from Kilimanjaro Christian Medical University College in Tanzania, Radboud University Medical Center in the Netherlands, and several other European and African institutions.