Important gaps remain in our understanding how diet and the composition of the gut microbiota influence the function of our immune system. TransMic focused on communities in sub-Saharan Africa that are in different stages of urbanization and a nutrition and epidemiologic transition. These communities offer unique opportunities to investigate the ‘diet-microbiome-health’ axis for the following reasons: a) differences in diet (‘Westernized’ vs traditional) and lifestyle (urban vs rural) are more extreme than in European populations; b) the traditional African diet is rich in plant-based fibers and immunomodulatory molecules (such as polyphenols), but also in fermented products rich in environmental microbes, which have been lost in the industrialized world and  are increasingly recognized to positively influence host defense mechanisms.

Data from cohorts from Tanzania (urban versus rural dwellers; Work Package1), Burkina Faso (rural, semi-urban, urban families; WP2) and Europe were used and analyzed using a multi-omics approach (WP3). In addition, a two-week dietary intervention was performed in healthy young Tanzanian men who were switched from a 'Western' to a traditional diet and vice versa or were exposed to a traditional fermented banana beverage (WP4). Omics-based data, including microbiome composition, genetics, transcriptome, metabolome and plasma proteome were integrated with functional immune data.

Key findings were that changing a traditional plant-rich diet to a calorie-dense ‘Westernized’ diet affects plasma metabolites, the composition of the gut microbiome and the function of the immune and coagulation system. The intervention study confirmed the causal effects of diet on immune function and  showed the immunomodulatory effects of a switch from an urban (‘high caloric, western style’) to a rural (‘traditional plant-rich’) diet and vice versa, and a strong immune effect of intake of a traditional fermented banana brew.

Overall, TransMic shows that the switch from a traditional – largely plant-based –  diet to a high-calorie 'Western' diet has a marked influence on the function of the immune- and coagulation system, via changes in active metabolites in the blood and the composition of the gut microbiome. These changes lead to an increased activation of the immune system. In Europe, the transition to a 'western' diet has had a negative effect on the diversity of the microbiome. TransMic  shows that dietary interventions can contribute to the restoration of a healthy microbiome composition and a more balanced immune system.

The TransMic project shows that rural-to-urban transition in Tanzania and Burkina Faso is associated with a switch in diet from a traditional – largely plant-based – African diet rich in fermented products to a high-calorie 'Western-style' diet. This switch has a marked influence on the function of the immune- and coagulation system via changes in active metabolites in the blood and the composition of the gut microbiome. A short dietary intervention study in healthy men in Tanzania confirmed that a switch from a urban to a traditional diet or the intake of a fermented banana beverage reduced inflammation and improved blood markers of cardiometabolic health. TransMic also shows that the genetic regulation of the immune system in East African individuals differs from that of people in Western Europe with East African individuals having a more activated immune and coagulation system. Sticking to a traditional, immunomodulatory diet may therefore be of extra importance for African communities in order to curb the present surge in inflammation-related conditions.