Dietary fiber — a name given to several different forms of carbohydrate that resist being broken down by the digestive process — has long been known to be good for digestive and intestinal health, for a number of different reasons. It may help with intestinal motility (movement of digested food through the intestines), slow the digestion of other forms of carbohydrate, reduce blood cholesterol levels by encouraging bile (a cholesterol-rich digestive fluid) to be excreted rather than reabsorbed, and improve the balance of healthy bacteria in the colon by acting as food for the bacteria. This last role of fiber — as food for bacteria — was the subject of the latest study. Researchers were interested in the effect of both fiber intake and milk intake on byproducts (known as metabolites) of tryptophan, a chemical found in many protein-rich foods. Some byproducts of tryptophan — created when gut bacteria break down the chemical — have been found to be harmful, potentially increasing the risk for type 2 diabetes, while other metabolites of tryptophan may be beneficial.
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Certain metabolites linked to lower type 2 risk
For the latest study, researchers looked at the effects of 11 different byproducts of tryptophan on the risk of developing type 2 diabetes, as well as what dietary factors affected levels of these byproducts. The participants were 9,180 people who took part in five different general health studies, and came from a variety of racial and ethnic backgrounds. The researchers found that four metabolites of tryptophan were linked to a higher risk of developing type 2 diabetes over time, while one metabolite was linked to a lower risk for type 2.
The researchers found that fiber intake was the strongest dietary factor responsible for a beneficial balance of tryptophan metabolites, linked to a lower risk for type 2. In fact, fiber intake was more strongly linked to a beneficial balance of these byproducts than intake of tryptophan itself — indicating that the balance of different types of gut bacteria, which is affected by fiber intake, explains which byproducts of tryptophan are created when bacteria break down the chemical. They also found that among people who carry a gene that’s linked to lactose intolerance, a higher milk intake actually increased levels of a beneficial type of bacteria called Bifidobacterium — as well as a beneficial balance of tryptophan byproducts, linked to a lower risk for type 2 diabetes.
These results show that in all people, a higher fiber intake may play a key role in reducing the risk of type 2 diabetes by affecting the levels of different gut bacteria that break down tryptophan — and that in people with a common gene linked to lactose intolerance, a higher milk intake may have a similar effect. More research on how different foods affect levels of gut bacteria may reveal more specific links between fiber-rich foods and diabetes risk — but for now, it’s a safe bet that consuming a variety of fiber-rich foods is a good way to reduce your risk for type 2 diabetes, and may improve your diabetes control and overall health if you already have the condition.
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