The title is a synopsis of this post. The key phrase there is “gut bacteria” which you can read about further down.

Press release: Metabolite Produced By Gut Microbiota From Pomegranates Reduces Inflammatory Bowel Disease, EurekAlert, 9 January 2019

Scientists at the University of Louisville have shown that a microbial metabolite, Urolithin A, derived from a compound found in berries and pomegranates, can reduce and protect against inflammatory bowel disease (IBD). Millions of people worldwide suffer from IBD in the form of either ulcerative colitis or Crohn’s disease.

Actual study: Enhancement Of The Gut Barrier Integrity By A Microbial Metabolite Through The Nrf2 Pathway, Nature Communications, 9 January 2019

We demonstrate that UroA and UAS03 exert their barrier functions through activation of … pathways to upregulate epithelial tight junction proteins. Importantly, treatment with these compounds attenuated colitis in pre-clinical models by remedying barrier dysfunction in addition to anti-inflammatory activities. Cumulatively, the results highlight how microbial metabolites provide two-pronged beneficial activities at gut epithelium by enhancing barrier functions and reducing inflammation to protect from colonic diseases.

The mechanism:

1. Eat food that contains ellagitannins (ETs) or ellagic acid (EA). Pomegranate and berries, especially raspberries, are high in EA. Chestnuts, walnuts, pecans, almonds, rose hips, grapes, cranberries, cherries, strawberries, and peaches also contain EA. More here: Phenol-Explorer and here.

2. Bacteria (certain bacteria, see below*) that live in the large intestine consume ellagic acid and give off urolithins.

3. Among urolithins, Urolithin A (UroA) was found to tighten junctions between cells that line the intestine. (Note the needle-and-thread in the graphic above.) Tight junctions prevent leaks into our body of microbes and chemicals that can cause inflammation, both locally in the intestines and systemically.

* There’s a sticking point. Only some bacteria produce UroA from ellagic acid:

The microbe Bifidobacterium pseudocatenulatum INIA P815 strain in the gut has the ability to generate UroA from ellagic acid (EA), a compound found in berries and pomegranates. Variations in UroA levels, despite consumption of foods containing EA, may be the result of varied populations of bacteria responsible for the production of UroA from one individual to another, and some individuals may not have the bacteria at all.

One researcher said that, for this to work, it “requires that we protect and harbor the appropriate gut microbiota and consume a healthy diet.” So, it’s not just about eating berries, it’s about promoting the growth of beneficial bacteria, specifically Bifidobacteria strains. Looking around I see that peas, beans, legumes, members of the onion family (onions, leeks, garlic), asparagus, chicory, artichoke, wheat, oats, barley, bananas, and low-fat diets can all increase this strain. But high-fat diets, especially saturated fat/animal fat, and animal protein can decrease it.

In the end, before you can benefit from ellegic acid, you have to establish good gut bacteria. Eating a low-fat, plant-based diet can do that.

I should say … The workaround for not having enough Bifidobacteria is to take UroA (or the synthetic UAS03) directly by mouth, which they found “significantly mitigated systemic inflammation and colitis suggesting potential therapeutic applications for the treatment of IBD.” But then you’re talking about drugs, and pharmaceutical profit.