α-linolenic Acid (ALA) prevents severe calorie restriction-mediated changes to the intestinal microbiota and epithelial architecture
Creators: name: Weninger, Alyssa
Publisher: name: The University of North Carolina at Chapel Hill University Libraries
Year: 2024

description: Objectives:
Extreme and chronic calorie restriction observed in severe acute malnutrition (SAM) and anorexia nervosa (AN) decreases the capacity of the gastrointestinal (GI) tract to absorb calories by altering gut morphology and microbiota composition. Previous studies have associated the lack of microbes within the Ruminococcus genus, particularly Ruminococcus gnavus, with malnourishment and failure to restore normal growth. Furthermore, the Carroll lab has demonstrated that monoassociating germ-free mice (mice raised in sterile conditions) with R. gnavus during severe calorie restriction protects against starvation-mediated morphologic changes to the gut epithelium. Ready to use therapeutic foods (RUTFs) are nutrient-dense supplements designed to reduce SAM mortality, yet their efficacy is variable as many malnourished children are unable to completely restore healthy growth and a diverse gut microbiota, necessitating improved treatments. In addition, clinical renourishment of patients with AN fails to restore a healthy gut microbiota and the metabolic capacity of this microbial community. Therefore, investigators have been testing the efficacy of microbiota directed complementary foods and have observed children with SAM experiencing improved growth while consuming fewer calories on these diets compared to those on conventional RUTFs.
This study sought to investigate the influence of a specific nutrient (the essential omega-3 fatty acid, alpha linolenic acid (ALA)) on the intestinal epithelium and microbes during caloric restriction. The choice of ALA is based on preliminary data that found that the intestinal epithelium switches its preference from glucose to fatty acid metabolism during severe caloric restriction. ALA is known to promote glucose absorption, nutrient transport, ISC proliferation, and alters the gut microbiota (marked by an increase in Ruminococcus gnavus). As R. gnavus monoassociation prevents gut architectural damage in calorie-restricted mice, this study hypothesizes that dietary ALA will prevent abnormal intestinal morphologic changes observed during severe calorie restriction, thereby aiding in weight maintenance, via the promotion of intestinal R. gnavus.

Methods: 16 B6/JAX mice were randomly distributed into one of four experimental groups (ad libitum control, 60CR control, AdLib ALA, and 60CR ALA) with 2 male and 2 female mice per group. All mice were placed on a control diet for 7 days to determine the amount of food consumed per day. Mice either remained on the control diet or were fed a diet enriched with ALA for 9 days. Half of the mice in each diet group were put on a 60% calorie restriction (60CR) diet (9 days) with 2 days of refeeding following restriction. Mice were weighed daily, and fecal samples were collected for qPCR analysis to quantify Ruminococcus abundance. Upon sacrifice, duodenum tissue was harvested, and H&E analysis was performed to assess gut morphology. To investigate the specific effect ALA has on R. gnavus, this microbe was grown in varying concentrations of ALA in vitro.

Results: In 60CR mice, ALA supplementation decreased weight loss, preserved gut morphology, and increased the abundance of Ruminococcus species. At 50 μM ALA supplementation in vitro, R. gnavus growth exceeded that of the control. As ALA concentration increased, R. gnavus growth decreased significantly, indicative of a possible threshold for the positive effects of ALA.

Conclusion: ALA supplementation minimizes weight loss, preserves gut morphology, and increases the intestinal concentration of R. gnavus. Isolating the effects of specific nutrients on individual gut microbes provides a scientific foundation for the development of individualized and more effective dietary treatments for malnutrition.