How intermittent fasting helps with weight loss and how many hours you should fast

Many experts suggest starting with a 12/12 routine: fasting for 12 hours and eating during the remaining 12 hours. This is ideal for beginners, as much of the fasting occurs during sleep, making it easier to adhere to. Studies indicate that fasting for 12 hours 10 to 16 hours can mobilize fat reserves and activate ketone production.

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The most common protocol is a 16-hour fast and an 8-hour eating window. Considerable research supports positive weight loss results in overweight or obese individuals.

For example, according to Women's Health, dietitians such as Alissa Palladino and Lisa Moskovitz point out that 16/8 can help structure your diet and facilitate a calorie deficit, a key factor in weight loss.

Progressing progressively

Dr. Hu (Harvard Health) recommends starting slowly with 12/12, progressing to 14/10, and then moving to a 16/8 regimen as your body tolerates it.

Similarly, at Mass General, it is suggested Start with 10 hours of fasting and gradually increase to 16, since the metabolic benefits stabilize beyond that duration.

Time-restricted feeding (6–8 h of eating)

Another alternative is to limit daily intake to a 6- to 8-hour window, which implies 16 to 18 hours of fasting.

Even more restricted benefits: 8–10 h of food

Circadian rhythm expert Satchin Panda recommends an 8- to 10-hour eating window (fasting 2 to 4 hours), aligned with the body's internal clocks, which promotes weight loss, metabolic health, sleep, and skin health.

Likewise, Dr. Sari Arponen, a specialist in microbiota and aging, states that A natural overnight fast of 12–13 hours is beneficial, and for greater effects it can be extended up to 16 hours, with only two meals a day.

Intermediate window of 8–10 hours

A recent study of prediabetic adults found improvements in fat loss and glycemic control when following 8- to 10-hour eating windows.

Summary comparison

• 12 hours (12/12) 12 hours Ideal for starting off gently
• 14–16 hours (14/10–16/8) 8–10 hours Effective for weight loss and improving metabolic parameters
• ≥16 hours (6–8 hours after meals) Very restrictive Can enhance results, but requires adaptation and supervision

For most people, 16-hour intermittent fasting (with an 8-hour eating window, 16/8) represents the most effective balance between weight loss success and daily feasibility. However, starting gradually (12/12 → 14/10 → 16/8) is a sensible strategy and recommended by international experts. Stricter guidelines, such as eating windows as short as 6–8 hours, may work for experienced users. but they should be approached carefully and preferably with professional supervision.

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With information from Women's Health

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