Recent insights have shown that there is a triangular relationship between the diet, immune system and intestinal microbiome, in which the gut microbiota is a substantial contributor to human metabolism and health. A better understanding of the relationship between dietary components, including food processing, and the activity of metabolites produced by the gut microbiota on the host, is an essential step in designing food that benefits human health. The nutrient composition of a diet is obviously of importance to health, but the way food is designed also plays an important role in how much reaches the colon, where it is metabolised by the microbiota. Therefore, this thesis describes the effects of different dietary components, (fibres, tryptophan, glucosinolates and polyphenols) on immune modulation during human digestion and fermentation with a main focus on activation of the Aryl hydrocarbon Receptor. The results give insight into the effects of food preparation and microbial fermentation on the potential health properties of food compounds.