Barley, which is abundant in soluble dietary fibre beta-glucan, has been purported to be beneficial for obesity prevention due to the microbial metabolism of dietary fibre in the gastrointestinal tract.
To investigate the role of gut microbiota in non-obese individuals consuming high levels of barley, a cross-sectional study co-funded by grains manufacturer Hakubaku Co Ltd was conducted by researchers in Japan.
The analysis included 185 participants aged between 20 and 64, with a median barley intake of 3.494g/1000 kcal. Based on this, the participants were stratified into low and high barley consumption groups.
Within the high barley intake group, non-obese individuals (BMI less than 23) were categorised as responders, while those with obesity (BMI above 25) were designated as non-responders.
Comprehensive physical examinations, including blood tests, and separate assessments of gut microbiome profiling and dietary intake, were carried out.
Among the fermented food choices, responders had notably higher consumption of natto (fermented soybeans) than non-responders.
It was found that Butyricicoccus (gut butyrate-producing bacterium) and Subdoligranulum (butyrate-producing organism associated with short-chain fatty acids (SCFAs)) were significantly more abundant in the intestines of responders.
This suggests that butyrate synthesis could be enhanced in the gut of barley responders.
In a previous study, reduced levels of butyrate in faecal samples have been observed in obese individuals, compared to those with normal weight. Hence, the prevalence of SCFA-producing bacteria may be advantageous for combatting obesity.
“Our findings highlighted the distinctive characteristics of intestinal bacteria in the responders. These individuals had elevated levels of butyrate-producing bacteria and a higher consumption of natto, potentially enhancing the conversion of dietary fibre into energy within the digestive system.
“These results shed new light on the role of barley beta-glucan in the gastrointestinal tract. The simultaneous consumption of barley and natto has emerged as a promising nutritional approach for obesity prevention,” the authors wrote.
Interaction between barley and natto
Bacillus subtilis (B. subtilis) is a glycolytic bacterium used to ferment soybeans into natto.
In this study, responders exhibited higher natto consumption and tended to harbour more B. subtilis in their intestines than non-responders.
The genus Bacillus comprises different bacterial species, some of which are often observed in the human gut. Therefore, a physicochemical association cannot be demonstrated between barley and B. subtilis purely based on the results observed in this study.
However, the significant interaction between barley and natto in responders may provide a more comprehensive explanation for the association between barley consumption and obesity.
“Bacillus in responders may efficiently convert barley beta-glucan to glycosides in the gastrointestinal tract, mediating the metabolic activity of other intestinal bacteria and activating the production of SCFAs.”
While Butyricicoccus and Subdoligranulum are common butyrate-producing bacteria, studies on their physiological roles are limited.
Further analysis revealed that Subdoligranulum remained abundant in the high barley-high natto intake group, even after adjusting for confounding factors. This shows that it may be a potent intestinal bacterium that defines the barley responder status.
“These results suggest that in barley responders, B. subtilis may create an environment in the digestive tract conducive to efficient energy conversion of barley dietary fibre by intestinal bacteria through the low molecular weight of barley beta-glucan.
“Although the timing of barley and natto intake was not investigated in this study, both foods being traditional Japanese cuisines may imply concurrent consumption. Further studies are warranted to elucidate how the timing of barley and natto intake affects intestinal bacteria and obesity,” the authors concluded.
Source: Frontiers in Nutrition
https://doi.org/10.3389/fnut.2024.1434150
“High barley intake in non-obese individuals is associated with high natto consumption and abundance of butyrate-producing bacteria in the gut: a cross-sectional study”
Authors: Satoko Maruyama, et al
