Eating walnuts regularly may help to protect people against ulcerative colitis (UC), a study in mice suggests.
But exactly how walnuts are metabolized and work in the colon is not fully understood.
Titled “Dietary Walnut Supplementation Alters Mucosal Metabolite Profiles During DSS-Induced Colonic Ulceration,” the study was published in the journal Nutrients.
Walnuts contain a variety of compounds thought to have health benefits, like anti-inflammatory properties. They have the highest levels of omega-3 fatty acid, an essential fat for good health, of any tree nut.
Previous studies have suggested that eating walnuts provides some protection against disorders ranging from colon cancer to heart disease to diabetes. Might these nutrient-rich nuts also have protective effects in ulcerative colitis?
To find out, researchers fed mice either a standard chow diet or a diet containing up to 14% walnuts, which is the equivalent of a human eating around two ounces (56.6 grams) — between 20 and 25 walnuts — per day.
After being on this diet for two weeks, the mice were treated with the ulcer-inducing chemical dextran sodium sulfate (DDS), making them a preclinical model of UC. The researchers then compared the intestines of mice fed either diet.
In animals with a walnut-free diet, ulcers took up about 15% of the area of their colons. In mice fed the 14% walnut diet, the ulcer area was down to about 5%. This relationship wasn’t perfectly dose-dependent — mice fed the lowest amount of walnuts (3.5%) actually had slightly more ulcers on average than control (no walnut) mice — but there was, overall, a statistically significant correlation between eating walnuts and having fewer ulcers.
This effect was even more pronounced when the researchers waited longer (10 days after DDS use rather than two, during which the mice continued eating the walnut-infused chow) before examining their colons. On that diet for four weeks, these mice “showed almost no evidence of remaining colonic ulceration,” the researchers wrote.
It’s important to note that the scientists could not say for certain whether the smaller ulcer areas seen was due to walnuts protecting against the formation of ulcers, or because the walnuts were prompting the ulcers that formed to heal more rapidly.
The team also analyzed metabolites present in the tissues and feces of mice fed walnuts or not, and found some important differences, such as higher levels of omega-3 fatty acids and kynurenic acid, potent anti-inflammatory molecules.
“Significant changes in metabolites levels present in both fecal samples and colonic mucosa indicate that regular walnut consumption may improve lipid metabolism and enhance the production of antioxidants in the colon,” the scientists wrote.
These results may help explain exactly why this effect was observed, but more research will be needed to say with any certainty what walnut components affected ulcers and to what extent.
“We are continuing our work to understand whether those metabolic changes are part of the protection,” Daniel Rosenberg, PhD, a professor at UConn Health and a study co-author, said in a press release. “We are not suggesting that people with ulcerative colitis be maintained on a large walnut diet between active flares. But, we are hoping that we’ll be able to determine the active compounds — nutrients, phytochemicals — in walnuts that cause protection.”
“It is reasonable to speculate that walnut consumption has provided the ‘at-risk’ colonic mucosa with a more protective milieu which may better withstand subsequent environmental insults,” the study concluded.
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