Certain bacteria in the human gut maintain states of either great abundance or near absence, and these alternative states are associated with factors such as ageing and body weight, reports a study in Nature Communications this week.

Intestinal microbes can have important effects on our health, but the underlying mechanisms are poorly understood. Leo Lahti and colleagues analysed gut microbial data from 1,000 western adults of different ages and health statuses, and found a gradual variation in the abundance of most bacteria. Certain microbes tended to be either abundant or nearly absent. These states appeared to be relatively stable, with intermediate abundance states relatively short-lived. Moreover, the researchers found that the alternative states were correlated with physiological and health-related factors such as ageing and body weight.

Further research will be needed to test whether the observed correlations between microbial abundances and human health are due to causal relations, and whether the alternative states can be used as markers of health status or disease susceptibility.