Whole grains alter intestinal serotonin production, study says

Adults consuming whole grain rye have lower plasma serotonin levels than people eating low-fiber wheat bread, according to a recent study by researchers at the University of Eastern Finland and the International Agency for Research on Cancer (IARC), and published in The American Journal of Clinical Nutrition.

The study explored how the consumption of whole grain rye modulates concentrations of different metabolites in the bloodstream. The study employed untargeted metabolite profiling, also known as metabolomics, which can simultaneously detect numerous metabolites, including those previously unknown, according to the study abstract.

For the first four weeks of the study, 15 adults ate six 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, participants gave blood samples, which were analyzed by a combination of liquid chromatography and mass spectrometry. The plasma metabolite profiles between the different diet periods were then compared, the study abstract said.

The consumption of whole grain rye led to significantly lower serotonin concentrations when compared to consumption of low-fiber wheat bread, the study said.  The researchers also tested in mice whether the addition of cereal fiber to the diet changes serotonin production in the intestine. The diet of the mice was supplemented for nine weeks with rye bran, wheat bran, or cellulose flour. The mice receiving rye or wheat bran had significantly lower serotonin in their colon.

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

Eating whole grain 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.