Junk food rewires children’s brains, study finds

A new study has given the most direct evidence yet that ultra-processed foods (UPFs) change how children’s brains respond to food, and that this change helps drive weight gain.
It comes as the Supreme Court weighs warning labels on junk food, and as nutrition policy experts say the government has not acted on a proposal to restrict advertising of these products to children. Published in the Journal of the American Medical Association (JAMA), the latest study was led by researchers at the University of Southern California and Kaiser Permanente. It followed 46 healthy-weight children, with a mean age of 8.7 years, and used functional MRI to measure how their brains reacted to food cues.
Children who ate more UPFs, foods that are made industrially with typically high sugar, salt and fat, have little nutrient value and contained one or more additives, showed stronger responses in the dorsal striatum, the brain region linked to habit formation and reward-seeking.
A stronger response predicted a rise in body mass index (BMI) and body fat percentage over the following year. When the researchers accounted for this brain response, the link between UPF intake and weight gain weakened, which suggests it is a key pathway.
The authors say added sugar alone is unlikely to explain the effect. Experimental work indicates that the fat-and-carbohydrate combinations typical of UPFs trigger more reward signalling than either does alone.
“This study moves the debate from obesity to addiction,” said Dr Arun Gupta, convenor of the Nutrition Advocacy in Public Interest (NAPI) and co-author of the 2025 Lancet Series on Ultra-Processed Foods.
UPFs, he said, “are not just making children fat,” they are “changing the way their brains respond to food.” The finding adds to a growing body of research showing the health toll of UPFs. A BMJ meta-analysis of 8.8 million adults linked UPF consumption to a 24 per cent higher risk of cardiovascular events, 12 per cent higher cancer risk and 18 per cent higher all-cause mortality.
A BMC Medicine study of 4,000 children found that UPF intake at age 3 predicted greater weight gain by age 10-11. In India, the Indian Medical Council Research (ICMR)- INDIAB study found that one in four Indians is diabetic, pre-diabetic or obese, and attributed 56.4 per cent of the disease burden to unhealthy diets.
The Supreme Court is hearing a PIL by 3S and Our Health Society seeking mandatory front-of-pack warning labels on foods high in sugar, salt and saturated fat. In February, it asked the Food Safety and Standards Authority of India (FSSAI) to consider such labels.