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Special Reports May 2017 Issue

Nourishing Your Microbiota

Page 2: What Microbes Produce and Eating for Trillions

What Microbes Produce:

When microbes ferment fiber, they produce short-chain fatty acids (SCFAs). Some of the main ones are acetate, propionate and butyrate. "SCFAs support the immune system and gut health," Meydani says. "And, some of them have anti-inflammatory effects." Over the long term, too much inflammation in our body is associated with increased risk of heart disease, type 2 diabetes and certain cancers.

Recently, Meydani and colleagues completed a trial in which they fed 81 healthy men and postmenopausal women (age 40 to 65) a diet that was either rich in whole grains or refined grains (primarily wheat) for six weeks. Whole-grain wheat is a good source of fiber, including a type called inulin, which is a prebiotic. In refining wheat, more than half (58%) of the fiber is lost.

All food was provided to people in the study and in amounts to maintain their weight. Except for the type of grains, both groups ate the same foods. The whole-grain group averaged 40 grams fiber daily; the refined grain group, 21 grams.

"In the whole-grain group compared to the refined grain group, we saw a modest change in the gut microbiota (based on analyzing stool samples), including an increase in bacteria that produce SCFAs that have anti-inflammatory effects," Meydani says. "However, we didn’t see an overall decrease in inflammation when we looked at the gut or throughout the body."

She explains that may be because the changes in the gut microbiota and their products weren’t enough to cause a pronounced effect on inflammation. Also, the time period people ate the whole-grain diet may not have been long enough for a stronger benefit. Other human trials of diet effects on the gut microbiota have typically shown modest effects over the short term, too (unless diet is drastically changed).

"We saw other benefits of consuming whole grains that were independent of the immune system and inflammation," Meydani adds. "For example, people on the whole-grain diet had a significant increase in their stool weight (which makes elimination easier) and frequency of stools." The research was published in the American Journal of Clinical Nutrition.

Eating for Trillions:

To nourish your microbiota, Holscher recommends following the government's MyPlate guidelines (or Tufts' MyPlate for Older Adults), including trying to eat more fruits, vegetables, whole grains, legumes and nuts. "Really eat the rainbow - getting a variety of colorful plant foods," Holscher says. "Remember, each plant food contains varying fibers that support different microbes, so getting a variety can help support a healthier gut microbiota."

She urges people to focus on eating whole plant foods rather than purchasing supplements or other special food products. By eating the whole food, you get phytonutrients, which may also support the microbiota. Plus, focusing on unprocessed and minimally processed foods avoids the risk that processing may have changed the fiber in a way that reduces the ability of the microbiota to utilize it.

Lastly, don't limit your selection of plant foods to examples listed as containing prebiotics, left. Inulin, one prebiotic, is found in hundreds of plant foods, although in smaller amounts in some. "Also, even if a fiber isn't fermentable and is not able to provide a specific prebiotic effect, the fiber can still provide a benefit in your gut," Holscher says. "For example, the fibers in celery aren’t generally fermentable by microbes, but the fibers can still help with regularity, which also supports gut health." So, enjoy a wide variety of plant foods.

To learn more: American Journal of Clinical Nutrition, March 2017

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