Can glutamine supplementation enhance the effects of a low-FODMAP diet? Original paper

There are many causes of irritable bowel syndrome (IBS), and the molecular mechanisms behind the condition are not well understood. However, dietary intolerances, modulation of the gut microbiome, and increased intestinal permeability have been identified as risk factors.^[1][2] A low-FODMAP diet (FODMAPs are types of carbohydrates that are poorly absorbed by the small intestine) reduces gastrointestinal symptoms in most people with IBS, but the response varies among individuals, and some report zero benefit, which warrants new strategies for managing the condition.

Glutamine is a nonessential amino acid that is a preferred energy source for intestinal cells. Evidence suggests that glutamine supplementation reduces intestinal permeability and alters the composition of the gut microbiota.^[3][4] Could glutamine supplementation enhance the effects of a low-FODMAP diet?

In this 6-week randomized controlled trial, 50 participants (average age of 38) with IBS and a normal body mass index were advised to consume a low-FODMAP diet and assigned to take 15 grams of either glutamine powder or whey protein isolate powder (the control). The powders were ingested as 5-gram doses three times per day.

The primary outcome was the change in IBS-Symptom Severity Score (IBS-SSS), a questionnaire that assesses the severity and frequency of abdominal pain, abdominal distension (bloating), satisfaction with bowel habits, and how much IBS interferes with quality of life using a visual analog scale. The secondary outcomes were changes in individual items within the IBS-SSS; stool frequency; stool consistency, assessed using the Bristol Stool Form Scale; and quality of life, assessed using a 34-item self-report specific to IBS.

IBS-SSS scores improved at least 45% in 22 of 25 (88%) participants in the glutamine group, while 15 of 25 (60%) improved in the control group.

Regarding individual items within the IBS-SSS score, the glutamine group saw greater improvements in “dissatisfaction of bowel habit” and “interference with community function” than the control group. Quality of life, stool frequency, and stool consistency improved in both groups compared with baseline, with no difference between groups.

The use of whey protein as the control was a questionable decision. The researchers did not elaborate on the product used, other than it was an isolate. While whey protein isolates undergo more extensive processing than whey protein concentrates, thus reducing the lactose content, there may have still been enough lactose present to influence the results.

Also, the researchers did not adjust for multiple comparisons, despite the inclusion of numerous outcomes, which increases the risk of false-positive results. The secondary outcomes should be considered exploratory.