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IBS and IBD share symptoms such as diarrhea, constipation, bloating, and abdominal pain, but unlike IBS, IBD is consistently associated with inflammation and oxidative stress. Biophenols (aka polyphenols) are phytochemicals with antioxidant and anti-inflammatory properties, but though they have been shown to interact with the gut microbiota, their effects on gastrointestinal conditions are unknown.

The study

This meta-analysis assessed 23 parallel or crossover randomized placebo-controlled trials with a total of 25 interventions. All 1,566 participants were diagnosed with IBD (either mild to moderate UC or unspecified IBD) or IBS.

Peppermint oil was studied the most, with other interventions using aloe vera, anise oil, curcumin, ginger, mastic tree, pomegranate peel, resveratrol, soy isoflavones, wheat grass, yarrow, or a biophenol blend.

Gastrointestinal symptom scores (GIS) were measured using visual analog scales and condition-specific tools. The other outcomes were quality of life, adverse events, and markers of inflammation (calprotectin, CRP, IL-6, IL-8, and TNF-α) and oxidative stress (superoxide dismutase and oxidized LDL-C).

The results

Peppermint oil improved gastrointestinal symptoms in IBS. Resveratrol improved gastrointestinal symptoms and quality of life in IBD.

Markers of inflammation and oxidative stress were only measured in IBD. Aloe vera, mastic tree, resveratrol, and yarrow improved CRP. In one trial, resveratrol and ginger improved malondialdehyde (a marker of oxidative stress the authors didn’t list in their initial outcomes), but total antioxidant capacity wasn’t affected. In one trial, mastic tree reduced oxidized LDL-C, whereas resveratrol reduced TNF-α and superoxide dismutase.

Adverse effects such as bloating, constipation, diarrhea, heartburn, and nausea occurred in 19 of the 23 trials, but were mild to moderate. There were 80 adverse events in the intervention groups and 46 in the control groups, but this difference was not found to be statistically significant (the authors’ confidence in that finding, however, was low).

Dietary intake was not controlled or accounted for in any of the trials. Except for peppermint oil and resveratrol, the evidence is too limited to support broad recommendations for biophenol supplementation in IBS or IBD. Optimal dosing has not yet been determined for any of these biophenols.


The authors reported moderate to high levels of certainty and moderate to large effect sizes for both peppermint oil and resveratrol. Considering the long-term safety and mild side effects, these are cost-effective means of improving gastrointestinal symptoms and quality of life.

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This Study Summary was published on June 4 2021.