Asthma is a chronic disease of the airways, characterized by inflammation that is mainly caused by T-helper (Th) 2 cells. Current lifestyle recommendations of the Global Initiative for Asthma (GINA) include the consumption of a diet high in fruits and vegetables, and healthy weight maintenance. However, in the literature there are numerous nutritional intervention studies in asthma patients with beneficial outcomes, suggesting that other dietary interventions might be helpful as well.

Altogether this raises two questions:
1) which nutritional interventions improve asthma-related outcomes and
2) do these effects occur via immunomodulation?

Therefore, we systematically reviewed studies that reported both asthma-related outcomes as well as immunological parameters and searched for relations between these two domains. A systematic search identified 808 studies, of which 31 studies were included in this review. These studies were divided over six nutrition clusters: herbs, herbal mixtures and extracts (N=8); supplements (N=4); weight loss (N=3); vitamin D (N=6); omega-3 long-chain polyunsaturated fatty acids (LCPUFAs) (N=5); and whole food approaches (N=5).

Eighteen studies reported improvements in either asthma-related outcomes or immunological parameters, of which eight studies reported simultaneous improvements in both domains. Two studies reported worsening in either asthma-related outcomes or immunological parameters. One of these studies, using soy isoflavone supplementation, reported a worsening in both domains. The most promising interventions used herbs, herbal mixtures or extracts, and omega-3 LCPUFAs. However, as compared to the minimal clinical important difference (MCID), only a limited number of interventions resulted in relevant results.

Future studies should focus on further optimizing the beneficial effects of nutritional interventions in asthma patients, e.g. by considering the phenotypes and endotypes of asthma. The potential of promising nutritional interventions and underlying pathways should be explored further, before any of these interventions could be added to the current lifestyle guidelines for asthma patients.