Can intermittent fasting help you lose weight?

Last Updated : 10 August 2018
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    woman checking the hour on a clock

    Intermittent fasting describes a type of dieting that involves periods of routine fasting. This includes alternate-day fasting (ADF), where dieters typically have a ‘fast day’, where energy intake is strongly reduced (or no food is eaten), with a ‘feast’ day, where food is consumed without caloric restriction. Other popular examples are the 5:2 diet, which allows five days of eating without caloric restriction and two consecutive or non-consecutive ‘fast’ days, and the 16:8 diet, which restricts food intake to a single 8-hour period each day.1

    Research shows that intermittent fasting can be an effective strategy for weight-loss.1 However, these effects are probably due to an overall calorie deficit, as a result of a lower energy intake throughout the week, rather than an outcome of fasting periods.2 A study comparing fasting diets with calorie-restricted diets found that while intermittent fasting seemed effective for weight loss, it was not superior to calorie restricted diets.1 Furthermore, depending on your age, health and lifestyle, fasting, unless properly-managed, could have negative side effects. For example, it could result in a lack of concentration, low mood and tiredness due to insufficient energy intake on certain days.2 The World Health Organisation (WHO) recommends that energy intake (calories) should be balanced with energy expenditure to allow us to maintain an active and healthy lifestyle.3

    Is the wait worth the weight?

    Although intermittent fasting is unlikely to be sustainable for most of us in the long-term, if fasting periodically suits your lifestyle, then it might be an effective strategy for weight-management. Nevertheless, it should be carefully planned to meet all the nutritional needs set out in current dietary guidelines. If you are thinking of fasting, make sure to do it in a healthy and safe way by following current dietary guidelines and seeking the advice of a suitably qualified professional, like a registered dietitian, before you start.


    1. Headland, M., et al. (2016). Weight-Loss Outcomes: A Systematic Review and Meta-Analysis of Intermittent Energy Restriction Trials Lasting a Minimum of 6 Months. Nutrients, 8(6), 354.
    2. The British Dietetic Association (BDA, 2016) Top 5 worst celeb diets to avoid in 2017
    3. The World Health Organisation (WHO, 2015) Healthy diet