FAMILY meals often descend into ritual battles over healthy greens: how many children must consume, and how many treats they will earn as a result. The stakes may be higher than parents realise. According to a study published this week in Proceedings of the National Academy of Sciences, a sugary, fat-laden Western diet wreaks profound changes on children's gut bacteria, and could even promote the risk of asthma, allergies and other inflammatory diseases.

Rates of inflammatory disease have been rising for decades among adults and children alike. Puzzlingly, this increase has occurred largely in developed countries, bypassing poorer places. (Rural poverty brings many hardships; inflammatory bowel disease is not among them.) This has left scientists struggling to pinpoint exactly what about the rich world is making people sick. New data from Paolo Lionetti, of the University of Florence in Italy, supports the view that diet may be the culprit.

Dr Lionetti and his colleagues compared the diets and gut bacteria of 14 healthy children from a village in Burkina Faso with a group of 15 Florentine children. The differences were minimal at young ages, with breast-fed toddlers in both countries harbouring similar populations of gut bacteria. But among children who had graduated to the local diet, the two groups diverged dramatically. In Africa fibre-rich meals of millet, legumes and other vegetables (enlivened by the occasional termite) fostered a diverse mix of bacteria. European children, who imbibed typically Western doses of sugar, fat and meat, had fewer microbial species.

On top of this overall drop in diversity, the researchers saw striking trends in the types of bacteria in the two groups. Though healthy, Italian children harboured more than three times as many species associated with causing diarrhoea, leading the researchers to speculate that reduced intestinal diversity could permit unwelcome bugs to gain a foothold. The Italians also had bacterial profiles that indicate a greater risk of obesity. In contrast, African children had lots of bacterial species associated with leanness, and a higher proportion of microbes known to produce beneficial chemicals called short-chain fatty acids (SCFAs). Such compounds have been associated with lower levels of allergies and inflammation.

To show that these distinct bacterial populations could affect children's health, the researchers measured SCFA levels. The children from Burkina Faso were found to have more than double the concentration of their Italian counterparts. This hints that healthy bacterial populations living in the gut may not just exclude disease-causing bugs; by pumping out beneficial compounds, they may actively help to suppress disease.

Though the researchers did not measure health outcomes directly, their findings arrive amid growing evidence that gut bacteria control important immune functions. In preliminary studies researchers are testing whether doses of beneficial bacteria could alleviate bowel disease and eczema. While scientists puzzle out the details, parents can approach dinnertime negotiations with renewed determination.