Following a six week period where participants adhered to their habitual diet, they consumed a diet where all grain products were refined varieties for another eight weeks. The other group completed the study in the reverse order. Blood tests were done to assess gut microbiome composition, insulin sensitivity, glucose and lipid metabolism, gut functionality, inflammatory markers.
Why whole grains are healthy
Inflammation is the natural response of the body to an infection, but some people have slightly elevated levels of inflammation (so-called low-grade inflammation) even though there is no infection. In overweight people, an increased level of 'unnecessary' inflammation may lead to increased risk of developing type 2 diabetes.
The study findings show that this unnecessary inflammation was reduced significantly with whole grains.
- Blood tests showed that the participants had less inflammation in their bodies when eating whole grains.
- In particular, it appeared that rye had a beneficial effect on the blood's content of inflammatory markers.
- Satiety after a meal increased after a whole grain diet leading to reduced food intake.
- Whole grains decreased body weight, serum inflammatory markers, interleukin and C-reactive protein levels.
"Our analysis confirmed that there is a sound scientific basis for the dietary recommendation to eat whole grains. This may particularly apply to people, who are at increased risk of developing cardiovascular disease or type 2 diabetes," Professor Tine Rask Licht from the National Food Institute says.
"A good idea for future studies would be to examine the effect of various grain types," Tine Licht adds.
Impact of Whole Grains on Gut Bacteria
The research team used DNA sequencing to analyze stool samples from the participants in order to examine whether the different diet types affected the participants' gut bacteria composition. Overall, the analysis did not show major effects of the dietary grain products on the composition of the gut bacteria
"However, even though the analysis did not reveal significant changes in the average gut microbiota after whole grain consumption, it may well be that the individual components of our gut microbes have an impact on the individual reaction of our body to dietary whole grains, given that our bacteria help us digest the fibres in the whole grains. This is something that further studies of our data may answer," Tine Rask Licht explains.
- Henrik Munch Roager et al., Whole grain-rich diet reduces body weight and systemic low-grade inflammation without inducing major changes of the gut microbiome: a randomised cross-over trial, Gut (2017). http:dx.doi.org/10.1136/gutjnl-2017-314786.