Dr Joshua Bell, senior research associate in epidemiology and lead author of the report, said: “We knew that fat gain is harmful for health, but we didn’t know whether gaining muscle could really improve health and help prevent heart disease. We wanted to put those benefits in context.”

The findings showed that gaining fat mass was strongly and consistently related to poorer metabolic health in young adulthood, as indicated, for example, by higher levels of harmful cholesterol. These effects were much larger (often about 5-times larger) than any beneficial effect of gaining muscle. Where there were benefits of gaining muscle, these were specific to gains that had occurred in adolescence – suggesting that this early stage of life is a key window for promoting muscle gain and reaping its benefits.

Read the full University of Bristol press release