In this interview, Liam O’Mahony explores how diet influences the immune system through the metabolic activity of the gut microbiota. Rather than acting only as a direct source of nutrients, food provides substrates that intestinal microbes transform into bioactive molecules capable of modulating immune responses.

A key example was tryptophan metabolism. Gut bacteria can both metabolize dietary tryptophan into a broad range of indole derivatives and, in some cases, produce tryptophan themselves. This microbial contribution may be particularly relevant because bacterial indoles such as indoleacrylic acid and indolepropionic acid were shown to reduce the secretion of Th2-associated cytokines, including IL-5, IL-13 and IL-4, in stimulated lymphocytes. These effects were partly mediated by the aryl hydrocarbon receptor, but also involved the preservation of mitochondrial function, helping activated immune cells avoid excessive reactive oxygen species production and cellular damage.

The interview also addresses the overlap between asthma and obesity, highlighting their additive effects on inflammation and gut microbiome alterations. In this context, dietary patterns, especially low fibre intake in early life, may contribute to reduced production of protective metabolites such as short-chain fatty acids.

Finally, early-life peanut consumption was discussed as a potential model of immune protection during complementary feeding. Beyond antigen exposure, peanut provides fibre and phytochemicals that can be fermented by gut microbes, promoting short-chain fatty acid production and supporting microbial shifts associated with reduced allergic responses. Overall, the interview emphasized that many of the molecules required for immune regulation are not simply present in food, but are generated through microbial transformation, with important implications for preventing allergies, asthma and obesity-related inflammatory damage.