Whole Grains Reduce Intestinal Serotonin Production Linked to Diabetes and Colorectal Cancers

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Adults consuming whole grain rye have lower plasma serotonin levels than people eating low-fiber wheat bread, according to a recent study. In the study, conducted by the University of Eastern Finland and the International Agency for Research on Cancer (IARC), the consumption of cereal fiber from rye or wheat was also found to reduce serotonin levels in the colon of mice. In light of the results, the health benefits of whole grain cereals may be linked, at least in part, to the alteration of serotonin production in the intestines, where the majority of the body’s serotonin is produced. The results of were published in The American Journal of Clinical Nutrition.

The consumption of whole grain cereals has been associated with a lower risk of type 2 diabetes, cardiovascular disease and some cancers, but the underlying mechanisms are still poorly understood. There may be effects on bioactive compounds contained in whole grains, phytochemicals and fibers from which different metabolites are produced by intestinal bacteria.

The new study explored how the consumption of wholegrain rye modulates concentrations of different metabolites in the bloodstream. For the first four weeks of the study, the participants ate 6 to 10 slices a day of low-fiber wheat bread, and then another four weeks the same amount of wholegrain rye bread or wheat bread supplemented with rye fiber. Otherwise, they didn’t change their diet. At the end of both periods, blood samples were analysed to compare plasma metabolite profiles between the different diets.

Consumption of wholegrain rye led to, among other things, significantly lower serotonin concentrations when compared to consumption of low-fiber wheat bread.

When the researchers reproduced the test with mice, those receiving rye or wheat bran also had significantly lower serotonin in their colon.

While serotonin is best known as a neurotransmitter in the brain, serotonin produced by the intestines remains in the body, serving various peripheral functions including modulation of gut’s motility. Increased blood serotonin has also been associated with high blood glucose levels.

“Whole grain is known to reduce the risk of diabetes, and on the basis of these new results, the effect could at least partly be due to a decrease in serotonin levels,” says Academy Research Fellow Kati Hanhineva from the University of Eastern Finland.

The researchers are also interested in the association of serotonin with colorectal cancer.

“Some recent studies have found cancer patients to have higher plasma serotonin levels than healthy controls,” Scientist Pekka Keski-Rahkonen from IARC adds.

The consumption of wholegrain rye bread was also associated with lower plasma concentrations of taurine, glycerophosphocholine and two endogenous glycerophospholipids. In addition, the researchers identified 15 rye phytochemicals whose levels in the bloodstream increased with the consumption of rye fiber.

Source: Pekka Keski-Rahkonen, Marjukka Kolehmainen, Jenni Lappi, Valerie Micard,et.al. Decreased plasma serotonin and other metabolite changes in healthy adults after consumption of wholegrain rye: an untargeted metabolomics study. The American Journal of Clinical Nutrition, 2019; DOI: 10.1093/ajcn/nqy394

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