US Army exploring how stressors affect gut health in soldiers

© iStock/Maksym Dragunov

The mental and physical stresses associated with military training may be detrimentally affecting the health of the gut in US soldiers, potentially opening doors to nutritional interventions.

Data published in American Journal of Physiology - Gastrointestinal and Liver Physiology indicated that the stressors experienced during military training may impact the composition of the gut microbiota and metabolic activity, and increase intestinal permeability (IP) that is associated with inflammation.

“Observed associations between increased IP, the pre-stress microbiota, and stool metabolites associated with the microbiota suggest that targeting the intestinal microbiota could provide novel strategies for maintaining intestinal barrier integrity during physiologic stress,” wrote the scientists, led by J. Philip Karl, PhD, RD, from the U.S. Army Research Institute of Environmental Medicine Military Nutrition Division.

In an email to NutraIngredients-USA, Dr Karl said: “Our work is currently aimed at characterizing the impact of different military-relevant stressors on the gut microbiome.  However, moving forward we do plan to test different nutrition-based approaches for targeting the gut microbiome to benefit Warfighter health.”

Study details

The scientists used a systems biology approach to assess the impacts of a four-day cross-country ski march on the composition of the gut microbiota and metabolic activity, and intestinal permeability in 73 soldiers eating three rations per day.

“To our knowledge, this study is the first to examine intestinal microbiota responses during military training, and expands knowledge regarding the temporal effects of exercise and psychological stress on the microbiome, which is largely limited to animal studies at present,” they explained.

Results showed that intestinal permeability increased by a whopping 62%.

“Ultimately, the increase in IP is thought to result in mild endotoxemia and inflammation, and contribute to gastrointestinal distress in endurance athletes and possibly military personnel,” explained Dr Karl and his co-workers. “Gastrointestinal distress, to include infectious diarrhea, is historically the leading non-battle injury encountered in deployed military personnel, representing a significant burden to military health care and operational readiness. Identifying mediators of intestinal barrier responses to severe stress, and developing strategies to target those mediators may therefore have substantial benefit for military personnel.”

Gut microbiota changes

Analysis of the gut microbiota showed that the ski march led to an increase in levels of less dominant bacteria, some of which are considered potential deleterious and infectious, including Peptostreptococcus, Staphylococcus, Peptoniphilus, Acidaminococcus, and Fusobacterium.

On the other hand, a decrease in levels of bacteria considered beneficial because of their ability to deter pathogen invasion, reduce inflammation and promote immunity was also observe. These included Bacteroides, Faecalibacterium, Collinsella, and Roseburia.

“[A]lthough findings are correlative and the study design precludes determining causality, the observed associations between the pre-stressed microbiota and changes in IP during stress are plausible and provide potential targets for further study,” wrote the researchers.

The study was funded by the U.S. Army Medical Research and Material Command, the U.S. Defense Health Agency, and the Norwegian Defense Research Establishment.

Source: American Journal of Physiology - Gastrointestinal and Liver Physiology
Published online ahead of print, doi: 10.1152/ajpgi.00066.2017
“Changes in intestinal microbiota composition and metabolism coincide with increased intestinal permeability in young adults under prolonged physiologic stress”
Authors: J.P. Karl et al. 

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