A Western-style diet altered immune and metabolic function within 14 days in participants of a new study published in Nature Medicine. The research, led by scientists from Radboud University Medical Center and Kilimanjaro Christian Medical University College, revealed spikes in inflammation and impaired immune responses.
Urbanisation Drives Shift to Processed Foods in Tanzania
The study, conducted in northern Tanzania, examined how urbanisation is driving shifts from traditional plant-based diets to processed foods. “Inflammation is at the root of many chronic conditions, which makes this study highly relevant for Western countries as well,” said Quirijn de Mast, MD, PhD.
Impact of Urbanisation on Inflammation and Health Risks
Chronic inflammation underpins a range of serious conditions, including heart disease and type 2 diabetes. While past studies have often focused on the benefits of Mediterranean and Japanese diets, this research turns attention to African eating patterns.
“However, there is just as much to learn from traditional African diets, especially now, as lifestyles in many African regions are rapidly changing and lifestyle diseases are increasing,” said Mast. “Africa’s rich diversity in traditional diets offers unique opportunities to gain valuable insights into how food influences health.”
A Controlled Study of Dietary Impacts
Researchers conducted a randomised controlled trial involving 77 healthy men from the Kilimanjaro region, most in their mid-20s. The participants were assigned to one of three dietary interventions: rural men began consuming a Western diet, urban men adopted a traditional local diet, and a third group added the fermented beverage Mbege to their existing Western diet.
Blood tests taken at three intervals tracked changes in immunity, inflammation, and metabolism. The findings were adjusted for age, body mass index, and activity levels.
Western Diets Have Rapid and Measurable Health Effects
Participants who adopted a Western diet showed measurable biological changes within two weeks, including altered metabolic pathways, increased inflammatory markers, impaired immune cell function, and shifts in gene expression.
“Given that Westernised diets promote chronic diseases, this study’s results are unsurprising—processed foods drive inflammation, whereas healthy traditional diets rich in antioxidants and anti-inflammatory compounds help mitigate metabolic and immune dysfunction,” said Thomas M. Holland, MD, MS, a physician-scientist not involved in the study.
Some immune and metabolic disruptions persisted even four weeks after the diet had ended. Holland added, “Western diets are typically high in refined sugars, saturated fats, and processed foods, which can promote inflammation and oxidative stress and disrupt immune regulation.”
Foods featured in the Western diet included processed meats, French fries, fried chicken, pizza, pancakes, spaghetti, and white bread.
Traditional African Diets Provide Protective Benefits
Participants who switched to a traditional African diet or added Mbege, a fermented drink, experienced notable health benefits. Inflammatory markers decreased, immune responses strengthened, and metabolic health improved.
The traditional Kilimanjaro diet, which includes foods like green vegetables, legumes, plantains, and ancient grains such as millet and sorghum, is high in dietary fibre and polyphenols, known for their anti-inflammatory effects.
Acknowledging Study Limitations and Noteworthy Findings
The study’s relatively short duration and small, all-male sample size were key limitations, and the researchers noted that the unrestricted food intake during the intervention might have influenced weight and, subsequently, the results. Nevertheless, the biological changes observed were profound, suggesting that even brief dietary changes can significantly impact health.
Conclusion
The study highlights the growing need to preserve traditional, plant-based diets amidst the rapid urbanisation seen across the globe. Researchers pointed out the harmful impact of unhealthy Western diets on health. “At the same time, we show how harmful an unhealthy Western diet can be,” said Quirijn de Mast, MD, PhD.