We know we should eat less junk food, such as crisps, industrially made pizzas and sugar-sweetened drinks, because of their high calorie content. These “ultraprocessed” foods, as they are now called by nutritionists, are high in sugar and fat, but is that the only reason they cause weight gain? An important new trial from the U.S. National Institute of Health (NIH) shows there’s a lot more at work here than calories alone.