Common dietary emulsifiers promote metabolic disorders and intestinal microbiota dysbiosis in mice

Dietary emulsifiers are widely used food additives that stabilize emulsions in processed foods. Recent research has highlighted the crucial role of gut microbiota-host interactions in health and disease, prompting a reassessment of the safety of these additives. An imbalance in the gut microbiome (dysbiosis) is linked to various health issues, including metabolic syndrome and inflammatory bowel disease. This study focuses on four common emulsifiers – lecithin, sucrose fatty acid esters, CMC, and MDG – to examine their impact on glucose homeostasis, lipid metabolism, gut microbiota composition, and mucus layer integrity in a mouse model. The high levels of human exposure to these emulsifiers necessitate a thorough investigation of their potential adverse effects through the lens of gut-microbiota interactions. The study aims to address the gap in knowledge regarding the long-term effects of emulsifier consumption and to provide evidence-based insights into their potential health implications.

Existing literature indicates a link between dietary emulsifiers and various diseases. Studies have shown that emulsifiers like CMC and polysorbate 80 induce intestinal inflammation and metabolic syndrome by altering the gut microbiota and thinning the intestinal mucus layer, leading to increased gut permeability and lipopolysaccharide (LPS) levels. Human studies have also demonstrated that CMC consumption can reduce gut microbiota diversity, decrease beneficial metabolites, and increase bacterial encroachment into the inner mucus layer. However, the classification of emulsifiers varies across regulatory bodies, creating challenges for international comparisons of research. Dietary exposure estimates are lacking for many commonly used emulsifiers, especially those with high exposure levels like MDGs, lecithin, and CMC. Traditional safety assessments primarily relied on toxicological data, neglecting the crucial role of the gut microbiome. This study addresses this gap by comprehensively examining the effects of four commonly consumed emulsifiers on the gut microbiota and their relationship with obesity and metabolic diseases.

The study used two mouse models. In the first model, 15-week-old male C57BL/6JNarl mice were divided into four groups: control, lecithin (7523.3 mg/kg bw/day), sucrose fatty acid esters (1110 mg/kg bw/day), and CMC (1% in drinking water). These doses were based on estimated human dietary exposure levels, scaled up tenfold. The mice were fed a standard chow diet and received emulsifiers in their drinking water for 17 weeks. Body composition, blood biochemistry (glucose, insulin, cholesterol, triglycerides, liver enzymes), oral glucose tolerance tests (OGTT), and gut microbiota analysis (16S rRNA gene sequencing) were performed. An in vitro insulin resistance model using 3T3-L1 adipocytes was also employed to assess the direct effects of the emulsifiers on glucose uptake. In the second model, 8-week-old male C57BL/6JNarl mice were divided into two groups: control and MDG (5.5% in diet). Mice were calorie-restricted to ~85 kcal/week for 14 weeks. Similar assessments as in the first model were performed, along with confocal microscopy to visualize mucus layer thickness and bacterial location. Statistical analyses included ANOVA, t-tests, ANOSIM, and Spearman's correlation.

The study revealed that sucrose fatty acid esters and CMC induced hyperglycemia and hyperinsulinemia in mice, with CMC also increasing relative fat mass and decreasing lean mass. Lecithin, sucrose fatty acid esters, and CMC disrupted glucose homeostasis in the in vitro model. MDG impaired lipid and glucose metabolism. All emulsifiers altered gut microbiota diversity and composition. Lecithin, sucrose fatty acid esters, and CMC did not significantly impact mucus-bacterial interactions, while MDG showed a trend toward bacterial encroachment into the inner mucus layer and elevated circulating LPS. Specific findings include: * **Sucrose fatty acid esters and CMC:** Increased fasting glucose and insulin levels, higher HOMA-IR index, suggesting insulin resistance. * **Lecithin, sucrose fatty acid esters, and CMC:** Reduced 2-deoxyglucose uptake in vitro, indicating direct impact on insulin resistance. * **MDG:** Elevated serum cholesterol and reduced serum triglycerides, also led to higher blood glucose levels during OGTT. * **All emulsifiers:** Significant changes in gut microbiota α- and β-diversity, with specific genera altered by each emulsifier, and correlations between altered microbiota and metabolic biomarkers. * **MDG:** Trend toward shorter distance between bacteria and intestinal epithelial cells, along with significant increase in circulating LPS. The study also characterized the changes at the genus level, noting increases in disease-related bacteria and decreases in potentially beneficial bacteria for each emulsifier treatment. The findings are supported by statistical analyses presented throughout the study.

The results demonstrate that common dietary emulsifiers can negatively impact metabolic health and disrupt the gut microbiome. The observed effects vary depending on the specific emulsifier, with sucrose fatty acid esters and CMC causing prominent metabolic disturbances and MDG leading to alterations in lipid and glucose metabolism alongside gut dysbiosis and increased inflammation potential. The impact of these emulsifiers on gut microbiota appears to be a significant mechanism in driving these metabolic alterations. The relatively modest effects of lecithin may be because it's a natural emulsifier compared to the synthetic ones like CMC and the differences in how they're metabolized and interact with the gut. The findings highlight the importance of considering the gut microbiota in evaluating the safety of food additives and suggest that the current GRAS (Generally Recognized As Safe) guidelines, primarily based on toxicological data, may be inadequate for these compounds. Further investigation is needed to understand the precise mechanisms through which these emulsifiers exert their effects, including their interactions with specific gut bacterial taxa and their metabolites.

This study provides compelling evidence that common dietary emulsifiers, including lecithin, sucrose fatty acid esters, CMC, and MDG, have the potential to disrupt metabolic health and cause gut microbiota dysbiosis. The varying effects of different emulsifiers underscore the need for a nuanced approach to evaluating their safety. The results warrant a reevaluation of current food safety regulations and the consideration of gut microbiome effects in future assessments of food additives. Future research could focus on investigating the long-term effects of these emulsifiers, exploring the specific mechanisms of action, and developing strategies to mitigate their potential health risks.

The study utilized a mouse model, which may not fully translate to human responses. The high doses of emulsifiers used in some cases may not accurately reflect typical human consumption patterns, although they were based on estimates of human exposure scaled up. Calorie restriction in the MDG experiment is a limitation as it is not representative of free access feeding. The study's focus on a limited number of emulsifiers may not generalize to all emulsifiers. While the study identifies several correlation, more mechanistic study is needed to prove causal relationship between the results.