Unraveling the Role of Foods on Chronic Anti- and Pro-Inflammatory Cytokines: A Systematic Review of Chronic Dietary Intervention Trials in Humans.

BACKGROUND/OBJECTIVES: Unbalanced diets contribute to a rise in low-grade systemic inflammation, a risk factor for metabolic diseases. The aim of this study is to systematically review evidence from chronic intervention studies to understand the role of foods in modulating inflammatory responses in humans.

METHODS

A literature search was conducted on PubMed using specific keywords. Risk of bias was assessed using Cochrane guidelines. Inclusion criteria required chronic dietary intervention studies measuring cytokine levels in humans.

RESULTS

In the 75 studies selected, results revealed extremely high variability both in outcomes, study design, and participant selection criteria. Studies with fruits and vegetables showed a reduction in circulating cytokine levels and/or an increase in anti-inflammatory cytokines in 80% of studies (8/10), followed by fish (78%; 7/9), dairy (67%; 4/6), cereals (64%; 7/11), and oils (57%; 4/7). Beverages and hot beverages showed a decrease in circulating cytokines in 50% of cases (10/20 and 4/8, respectively). An increase in pro-inflammatory cytokines was observed in dietary interventions with beverages. As further findings, we also observed greater effectiveness from fruits and vegetables (87.5%; 7/8), fish (75%; 6/8), and cereals (62.5%; 5/8) when studies were conducted in subjects with pathologies or risk factors.

CONCLUSIONS

Fruits and vegetables, fish, and cereals reduce systemic inflammation mainly in subjects with pathologies or risk factors. However, the limited number of studies do not allow us to draw solid conclusions on individual foods. Standardized dietary intervention trials are urgently needed to understand the role of foods in modulating inflammatory responses and to deliver findings to the general public.