Does fasting help with weight loss?

Fasting may support weight loss for some people mainly by changing eating patterns and total intake; outcomes vary. Some studies also suggest fasting may boost metabolism slightly and improve hormone function to facilitate weight loss, such as by lowering insulin levels ( 35 , 36 ).

Can fasting improve metabolism?

Short-term fasting has been linked to temporary changes in stress hormones (including norepinephrine) in some studies ( 37 ). However, very long fasts (over 3 days) can have the opposite effect and slow down your metabolism. Theoretically, over time while practicing long fasts, the body adapts to conserve energy, entering a more energy-efficient state ( 38 ).

Strictly speaking, any food or drink containing calories will break a fast. This includes anything with carbohydrates, protein, or fat. The amount of calories needed to break a fast is debated, but most experts agree that anything over 5-10 calories will likely interrupt the fasting state.

Can you drink water or coffee while fasting?

Yes, water is essential and should be consumed freely during most fasts. Many people stick to water, plain tea, or black coffee during fasting windows; individual tolerance varies. However, adding sugar, milk, or cream will break your fast.

How often should you fast?

The frequency depends on the type of fasting. Time-restricted eating can be done daily. A 24-hour fast may be done once or twice a week. Longer fasts (48+ hours) should be done much less frequently, perhaps once a month or a few times a year, and ideally with medical guidance.