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Moderate evidenceWeight loss

Intermittent fasting

Intermittent fasting (5:2, alternate-day fasting or time-restricted eating) works for weight loss about as well as an ordinary calorie-controlled diet, but not better. It is one way to eat less, so choose it only if the schedule suits you.

What the science says

  • Same weight loss as daily calorie restriction Strong evidence

    Cioffi et al.'s 2018 meta-analysis of 11 randomized trials (8–24 weeks) found no meaningful difference in weight loss between intermittent and continuous energy restriction. In Liu et al.'s 2022 NEJM trial, 139 adults with obesity on the same calorie target lost 8.0 kg with an 8-hour eating window vs 6.3 kg without it at 12 months, a non-significant difference.

  • Alternate-day fasting is harder to stick to Moderate evidence

    In Trepanowski et al.'s 2017 one-year trial in 100 adults with obesity, alternate-day fasting and daily calorie restriction gave the same weight loss (6.8% at 6 months), but dropout was higher with fasting (38% vs 29%) and people ate more than planned on fast days.

  • A 16:8 eating window without calorie targets did little Moderate evidence

    In the TREAT trial (Lowe et al., 2020), 116 adults with overweight who ate only between noon and 8 pm for 12 weeks lost no more weight than those eating three regular meals, and lost slightly more lean mass.

How to apply it

Treat fasting as a scheduling tool for a calorie deficit, not as a separate fat-loss mechanism.

Time-restricted eatingEating window of about 8–10 hours, with the same calorie target
5:22 non-consecutive days at about 25% of maintenance, 5 normal days
ProteinStill 1.6–2.4 g/kg/day, packed into fewer meals
TrainingKeep lifting; plan sessions near a meal if fasting hurts performance

Who should be careful

Fasting is unsuitable for people with diabetes on glucose-lowering medication, those with an eating-disorder history and anyone pregnant or breastfeeding, unless supervised. Anyone with diabetes, high blood pressure or another obesity-related condition, a history of eating disorders, who is pregnant or breastfeeding, or who is considering weight-loss medication should plan weight loss with a physician or registered dietitian; this page gives no drug advice.

Frequently asked questions

Is intermittent fasting better than a normal diet for fat loss?

No. A meta-analysis of 11 trials and a 12-month NEJM trial found weight loss similar to ordinary daily calorie restriction.

Does 16:8 work without counting calories?

Not much in the TREAT trial: eating between noon and 8 pm for 12 weeks gave no more weight loss than three regular meals.

Who might prefer intermittent fasting?

People who find it easier to skip meals than to eat smaller ones. Alternate-day fasting had higher dropout than daily restriction, so test whether the schedule fits you.

Scientific references

More on weight loss

  • Rate of weight loss Moderate evidence

    For people who lift, losing about 0.

  • High-protein diet while dieting Strong evidence

    Eating more protein during a calorie deficit helps keep lean mass and gives a small extra fat loss compared with a standard-protein diet of the same calories.

  • Resistance training while dieting Strong evidence

    Lifting weights during a diet makes much more of the weight you lose come from fat instead of muscle, and it keeps or raises strength.

  • Cardio for weight loss Moderate evidence

    Cardio helps fat loss, but at typical doses it produces only a couple of kilograms on its own; clinically meaningful loss takes high volumes (more than about 250 minutes a week) or a calorie deficit alongside it.

  • Diet breaks and refeeds Moderate evidence

    Planned periods at maintenance calories in the middle of a diet are at least as effective as dieting continuously and may make the diet easier to tolerate.

  • Low-carb vs low-fat diets Strong evidence

    When calories and protein are similar, low-carbohydrate and low-fat diets produce about the same fat loss over a year or more.