- Intake of a diet rich in whole grains was associated with reduced energy intake and body weight and circulating markers of inflammation in adults at risk of developing metabolic syndrome.
- The amount of whole grain intake was directly related to reduction in fasting serum concentrations of interleukin 6.
- The whole grain-rich diet, compared to the refined grain diet did not significantly modify fecal microbiome composition.
Whole grain consumption is associated with decreased risk of several lifestyle-related diseases including type 2 diabetes and cardiovascular diseases. To investigate whether a whole grain diet alters the gut microbiome and insulin sensitivity, as well as biomarkers of metabolic health and gut functionality, a study was conducted among Danish adults.
The study included 50 adults at risk of developing cardiovascular disease or type 2 diabetes. The 50 study participants were divided randomly into two groups. One group consumed a diet for eight weeks, in which all grain products were whole grain varieties.
‘Whole grain diet reduced body weight and systemic low-grade inflammation but did not alter insulin sensitivity and gut microbiome.’
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.