Snacks constitute almost a quarter of a day’s calories in U.S. adults and account for about one-third of daily added sugar, a new study suggests.

Researchers analyzing data from surveys of over 20,000 people found that Americans averaged about 400 to 500 calories in snacks a day—often more than what they consumed at breakfast—that offered little nutritional value.

Though dietitians are very aware of Americans’ propensity to snack, “the magnitude of the impact isn’t realized until you actually look at it,” said senior study author Christopher Taylor, professor of medical dietetics in the School of Health and Rehabilitation Sciences at The Ohio State University.