Iron- and zinc-fortified millet does not harm toddlers' gut microbiome, Mumbai trial finds

Pearl millet bred to carry extra iron and zinc caused no detectable harmful changes to toddlers' developing gut microbiome — the trillions of bacteria, viruses and fungi in the digestive tract — a nine-month study in Mumbai's urban slums has found. Published in Nature Communications, the work is believed by its authors to be among the first to examine how bio-fortified crops affect the human gut microbiome.

The study was led by researchers at Cornell University's Joan Klein Jacobs Centre for Precision Nutrition and Health, with Indian collaborators Shobha A. Udipi and Padmini Ghugre of Mumbai's SNDT Women's University and Ramesh D. Potdar of the Centre for the Study of Social Change, a Mumbai-based NGO. Iron deficiency affects roughly one in four people worldwide and hits young children especially hard, slowing brain development and leaving the body open to infection. The standard fix, iron supplements, can boost harmful pathogens in the colon, inhibit beneficial microbes and cause diarrhoea, constipation and tarry stools, earlier research found. "We thought that a food-based approach could help us move away from one-size-fits-all supplementation strategies," said Saurabh Mehta, founding director at the Jacobs Centre and principal investigator on the study.

Working with farmers, the researchers used traditional cross-breeding to develop a pearl millet variety with almost three times the iron and zinc of standard millet. The trial enrolled 223 children aged 12 to 18 months; the SNDT team developed the millet-based foods and delivered them to 20 sites. By the study's end, children eating the fortified millet showed increased activity in microbial pathways linked to fighting pathogens — including production of natural antibiotic-like compounds — and to antioxidant metabolism, while markers linked to harmful bacteria were lower.

Unlike supplements, which need distribution infrastructure, bio-fortified crops can be grown and eaten the same way ordinary crops are. India produces more than 40% of the world's millets, which include pearl millet (bajra), sorghum (jowar) and finger millet (ragi).