 Children were challenged with calcium propionate or placebo through daily bread in a double‐blind placebo‐controlled crossover trial.Although there was no significant difference by two measures, a statistically significant difference was found in the proportion of children whose behaviours "worsened" with challenge (52%), compared to the proportion whose behaviour "improved" with challenge (19%).When propanoic acid was infused directly into rodents' brains, it produced reversible behavior changes (e.g.