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Exercising in early life alters gut microbes, resulting in a healthier brain and metabolism that lasts throughout adulthood. A study on rats showed juveniles that voluntarily exercised every day developed a more beneficial microbial structure compared to their lazy counterparts and adults – even if the adults exercised.

Researchers from the University of Colorado Boulder say their findings suggest there may be just a short timeframe where humans have the chance to optimise their lifelong health.

Gut microbes are essential to the development of the immune system and neural functions, adding up to five million genes to a person's overall genetic profile. A healthy collection of microbes promotes good health, and while the microbial community is changeable throughout life, it is particularly plastic at a young age.

In the study, which has been accepted for publication in the journal Immunology and Cell Biology, the team found exercise in the juvenile period increased the probiotic Lactobacillus and butyrate-producing bacteria.

Both of these are "multi-tasking microbiota", interacting with a variety of pathways to produce neural and metabolic benefits, the authors wrote. While both help to prevent inflammation in the gut and promote the intestinal barrier integrity, Lactobacillus "can reduce anxiety and depressive-like behaviour, alter brain chemistry, and inhibit fat accumulation".

They said that while exercise in adulthood could lead to these results independently of the gut microbiota, "early life exercise can recruit the microbial system, and perhaps produce a more robust, synergistic physiological response aimed at improving health during this window of opportunity".

Researchers could not tell exactly what age range this "window" was, but their preliminary findings suggest the earlier in life the better. "Exercise affects many aspects of health, both metabolic and mental, and people are only now starting to look at the plasticity of these gut microbes," said Monika Fleshner, senior author of the study. "That is one of the novel aspects of this research."

Agniezka Mika, lead author, added: "Future research on this microbial ecosystem will hone in on how these microbes influence brain function in a long-lasting way."