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High fibre diets, bacteria and obesity

Long term study shows bacterial diversity influences weight gain.

Could the bacteria in your gut affect weight gain? A recent study in International Journal of Obesity confirms that it does. In healthy people studied for around 9 years, a high fibre diet was associated with a diverse bacterial population in the gut and a lower weight gain. The study in twins also showed that family history accounted for less than half of the variability in weight gain. The authors suggest we should be doing more research into ways of making the gut bacteria population more diverse and discovering whether changing the bacteria population could be a novel therapy/prevention for obesity.

Gut bacteria ferment fibre in the diet in the large intestine and provide the body with short chain fatty acids. These are an energy source for the body and they may also signal fullness and influence immunity. Previous research suggests low bacterial diversity in the gut could be linked to obesity and to low fibre diets and but changes in diversity in healthy people over a long period have not been studied before. Studies of the bacterial population also suggest the ratio of Firmicutes to Bacteroides may be altered in obesity.

This study examined fibre intake and body weight of 1632 twins at the start and around 9 years later. At the end of the study they also analysed groups of bacteria called operational taxonomic units (OTUs), in the twins’ guts.

They found that subjects who had gained weight during the study had a lower diversity of gut bacteria. They also consumed less fibre. The relation between fibre intake and microbial diversity remained after adjusting for protein and fat intakes.

Overall 9 OTUs were altered by weight gain or loss. OTUs from the Firmicute families Ruminococcaceae and Lachnospiraceae were more common in subjects who had lost weight. OTUs from Bacteroides were found more often in those who had gained weight.

However, the latter could just be a marker for low microbial diversity, suggest the authors. The researchers also noticed that the effects of a high fibre diet on weight gain appeared to be greater for those with a greater microbial diversity.

Because the study didn’t examine gut bacteria at the start it cannot say bacterial diversity in the gut results in less weight gain or whether weight gain reduces diversity. Long term studies of gut bacteria and body weight are needed, say the authors.

 Gut microbiome diversity and high-fibre intake are related to lower long-term weight gain. C Menni, M A Jackson, T Pallister, C J Steves, T D Spector and A M Valdes. International Journal of Obesity advance online publication 4 April 2017; doi: 10.1038/ijo.2017.66


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