Why do you lose weight from celery?

Celery is often cited as a 'negative calorie' food, meaning it supposedly burns more calories to digest than it contains. While celery is very low in calories and high in water and fiber, the 'negative calorie' concept is largely a myth. The thermic effect of food (TEF) is real, but it's a small percentage of total calorie expenditure. For celery, the TEF is minimal, and it does not significantly contribute to weight loss beyond its low calorie count.