Caloric deficit
Clinical reviewer: Jacob Moore, MD · Last checked September 24, 2026
What is a caloric deficit?
Caloric deficit is a state in which the body uses more calories than it takes in from food and beverages. It is the reverse of the calorie surplus that NIDDK says leads to weight gain over time, when intake from food and drinks exceeds the calories used through daily activity.
How do calories in and out affect weight?
NIDDK explains that when people take in more calories from food and beverages than they use through physical activity and daily living, the body may store some of the extra as fat, and over time they will likely gain weight [1]. A caloric deficit is the opposite pattern: fewer calories in than out. WHO likewise describes overweight and obesity as the result of an imbalance between energy intake from diet and energy expenditure from physical activity [2].
Why doesn't weight loss from a deficit stay proportional over time?
A 2011 modeling study found that the body's weight response to a change in calorie intake is slow, with a half time of about one year, and that people with more body fat see a larger expected weight loss for the same change in intake [3]. Semaglutide, a GLP-1 medication, reduced how much people ate in one 12-week trial: it produced a 24% reduction in total energy intake across ad libitum meals compared with placebo, an effect the researchers linked to reduced appetite [4].
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This entry is for education and is not medical advice. Talk with a licensed clinician about your own situation before starting, stopping, or changing any treatment.
