Ad libitum feeding is an approach used in research studies where people — or animals in preclinical research — are given unrestricted access to food, meaning they can eat as much as they want whenever they choose. The term ad libitum originates from Latin, meaning “at will”.

This approach is used in research studies that aim to observe natural eating behaviors, spontaneous caloric intake, and satiety without imposing dietary restrictions. In contrast, restrictive feeding involves controlling or scheduling food intake.

For example, a randomized controlled trial by Gibson and colleagues gave adults a snack of either protein or carbohydrates before every major meal during a 5-day ad libitum feeding intervention.^[1] Food intake and satiety were measured at multiple time points, allowing the researchers to observe how the participants naturally regulated their food intake following a premeal snack of either protein or carbohydrates. Ultimately, the study found no significant differences in ad libitum food intake or satiety between the two conditions.