Carrageenan and insulin resistance in humans: a randomised double-blind cross-over trial.

Background: The potential impact of specific food additives, common in Western diets, on the risk of developing type 2 diabetes is not well understood. This study focuses on carrageenan, a widely used food additive known to induce insulin resistance and gut inflammation in animal models, and its effects on human health.

Methods: In a randomised, double-blind, placebo-controlled, cross-over trial conducted at a university hospital metabolic study centre, 20 males (age 27.4 ± 4.3 years, BMI 24.5 ± 2.5 kg/m) participated. The intervention involved oral intake of carrageenan (250 mg) or placebo in the morning and in the evening and each intervention lasted 2 weeks. The primary outcome measured was insulin sensitivity (using oral glucose tolerance test [OGTT] and hyperinsulinaemic-euglycaemic clamp). Additional end-points included whole body and hepatic insulin sensitivity, MRI-measured brain inflammation and insulin resistance, intestinal permeability (via lactulose-mannitol test and plasma zonulin levels), and gut microbiome composition. Immune-cell activation and pro-inflammatory cytokine release from peripheral blood mononuclear cells were measured.

Results: Overall insulin sensitivity did not show significant differences between the treatments. However, interactions between BMI and treatment were observed (OGTT-based insulin sensitivity index: p=0.04, fasting insulin resistance: p=0.01, hepatic insulin sensitivity index: p=0.04). In overweight participants, carrageenan exposure resulted in lower whole body and hepatic insulin sensitivity, a trend towards increased brain inflammation, and elevated C-reactive protein (CRP) and IL-6 levels compared to placebo. Additionally, carrageenan was associated with increased intestinal permeability. In vitro natural killer (NK-)cell activation and increased pro-inflammatory cytokine release were found after carrageenan exposure in the participant's peripheral blood mononuclear cells.

Conclusions: These findings suggest that carrageenan, a common food additive, may contribute to insulin resistance and subclinical inflammation in overweight individuals through pro-inflammatory mechanisms in the gut. Further investigation into the long-term health impacts of carrageenan and other food additives is warranted.

Trial Registration: NCT02629705.