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Annual Microbiome Issue: External Factors to Microbiome Health

Stress Affects the Ability to Efficiently Absorb Nutrients in the Digestive Tract


When fermentable carbohydrates are passing through the small intestine, not fully digested, they are rapidly fermented by the colon, by susceptible subjects. This malabsorption may be exacerbated by stress.

This study examined the effects of corticotropin-releasing factor (CRF) on fructose absorption and the resulting volume of water in the small intestine. It was performed on 20 healthy men and women through the use of a high fructose meal and intravenous CRF administration to mimic a stress response.

  • CRF administration resulted in significant increases in salivary cortisol for approximately 135 min.
  • Small bowel water content rose, peaking at 45 min after fructose ingestion with hydrogen breath testing peaking at 75 min.
  • Ascending colon volume rose 29% on average after CRF administration.
Key Message:

Stress exerts a powerful influence over the body’s ability to absorb nutrients, even in healthy subjects. The increased speed of bowel transit in response to stress results in nutrients reaching inappropriate portions of the digestive tract, with potential consequences including increased fermentation in the colon creating an increased volume of the ascending portion. While the effects of chronic stress were not evaluated, the stressful event resulted in a physiological response lasting for 135 minutes. One could surmise that those who experience stressful events more often than 135 minutes, would have chronic increased motility creating a situation of chronic malabsorption.

Key Points:
  • Stress has a powerful lasting effect on the small intestines ability to absorb nutrients.
  • When nutrients are presented to inappropriate bacteria high levels of fermentation in the digestive track are possible.
  • It is important to consistently reduce stress and eat meals in a relaxed stress free environment to promote healthy digestive processes.

Healthy Diet Impacts the Balance of the Microbiome and is Associated with Healthy Insulin Sensitivity and Weight


Gut microbiota are closely linked to weight and metabolic health. The authors sought to investigate the impact of a prebiotic food, flaxseed mucilage, on the gut microbiota and the balance within the microbiome. The changes in the microbiome were then analyzed in reference to changes in metabolic markers and overall weight.

58 women were randomized into a single-blinded, parallel-group, placebo controlled intervention for 6 weeks. Baseline metabolic markers were analyzed and compared to markers tested at the 6-week mark.

  • Serum C-peptide was reduced.
  • Insulin response during an oral glucose tolerance test improved.
  • Insulin sensitivity was improved.
  • Microbiota from the Firmicutes phylum decreased over the course of 6 weeks.
  • No direct link between the modification of the gut microbiome and metabolic health markers was discovered, but this association deserves further study.
Key Message:

The food eaten on a daily basis carries a powerful influence over the health and balance of the gut microbiome. It is important to understand the positive impact on metabolic health support, which is conveyed through appropriate prebiotic foods. It is also important to remember a deleterious impact on the microbiome is possible when choosing the wrong types of foods for consumption on a long term basis.

Key Points:
  • Prebiotic foods support the healthy balance of the microbiome, thus promoting healthy metabolic function with appropriate insulin sensitivity and blood sugar metabolism.
  • There is still a lot to learn about how the gut microbiome interacts with the rest of the body, necessitating further research in the future.
  • We do know that appropriate balance of the microbiome is associated with many health supportive end results.

Heartburn Medication May Modify the Balance of the Microbiome


Proton pump inhibitors (PPI) have been associated with Clostridium difficile infection (CDI), but the mechanism remains unknown. With the increased use of PPI medication, the authors sought to understand mechanisms which increase the incidence of CDI in those using PPI medication.

An open-label crossover trial was performed on 12 healthy volunteers to access whether PPIs affect the gastrointestinal microbiome over the course of 12 weeks. Fecal samples were taken at the start of the trial and every 4 weeks thereafter, with the sample at 4 weeks to determine baseline, an additional sample after 4 weeks of PPI use, and then a last sample after half the group stopped PPI use for 4 weeks.

  • The use of PPI medication did not alter microbial diversity significantly but changes in taxa associated with CDI and gastrointestinal bacterial overgrowth were noted.
  • No changes regarding bile acids were noted.
  • An increase in pathways corresponding to genes involved in bacterial invasion was identified.
Key Message:

The use of PPI medication looks to have a mechanistic cause of CDI and bacterial overgrowth through the promotion of pathways corresponding with genes involved in bacterial invasion of the gastrointestinal tract.

Key Points:
  • When taking PPI medication, it is important to monitor for the symptoms of CDI and bacterial overgrowth of the digestive tract.
  • Supporting the proper balance of microbial taxa in the gut, may provide support for GI health in the presence of PPI medication.

  1. Murray KA, Lam C, Rehman S, et al. (2016). Corticotropin-releasing factor increases ascending colon volume after a fructose test meal in healthy humans: a randomized controlled trial. 103(5):1318-1326. doi:10.3945/ajcn.115.125047. Available at:
  2. Brahe LK, Le Chatelier E, Prifti E, et al. (2015). Dietary modulation of the gut microbiota–a randomised controlled trial in obese postmenopausal women. Br J Nutr. 114(3):406-417. doi:10.1017/S0007114515001786. Available at:
  3. Freedberg DE, Toussaint NC, Chen SP, et al. (2015). Proton Pump Inhibitors Alter Specific Taxa in the Human Gastrointestinal Microbiome: A Crossover Trial. Gastroenterology. 149(4):883-885.e9. doi:10.1053/j.gastro.2015.06.043. Available at:
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