A current popular trend in weight loss is the fasting diet, sometimes called an intermittent calorie restriction diet. These diets are often touted as a more successful or less onerous alternative to a conventional weight loss diet based on continuous calorie restriction.

Two recent articles in The Australian ^{1, 2} are good examples of the rationale that is typically presented to explain the benefits of fasting diets – the theory is that by only restricting calorie intake for short periods, you can avoid triggering the unhelpful ‘famine response’ that is thought to occur with long periods of calorie restriction. The famine response is thought to be the cause of the tapering effect noted in weight loss. At first you lose weight more rapidly, but as you continue to restrict calories, weight loss slows as your body holds onto energy stores, acting as if there is a food shortage. There are suggestions made of the optimal ‘normal diet’ period between fasts to avoid triggering this famine response. Perhaps the most common 5:2 pattern (5 days normal diet, 2 days fasting) should be replaced by 2 weeks normal, 2 weeks fasting? ^{1, 2}

So, what does the research tell us? To lose weight and keep it off, are we better off eating less every day? Or trying regular, intermittent calorie restriction (5:2)? Or using severe intermittent calorie restriction (5 days decreased intake:2 days fasting)? In short, all of these approaches have been shown to be effective, but intermittent calorie restriction has not been proven to be more effective than conventional continuous dieting ^{4, 5, 6, 7, 8, 9}. Most studies have been carried out on sample groups of overweight or obese women, so we cannot necessarily apply these findings to other groups.

Intermittent fasting diets have also been shown to have similar beneficial effects to continuous calorie restriction diets in controlling Type 2 Diabetes ^{2, 3, 6}.

The research is still unclear on whether intermittent calorie restriction diets are better than continuous calorie restriction for losing body fat but maintaining lean muscle mass ⁵. Some studies suggest yes, while others show the reverse, so the question remains unanswered ⁸.

So, looking at the research available to date, the best diet is definitely - whichever one you can stick to! Some advocates of fasting diets suggest they are easier to stick with, because there is a scheduled break from dieting. Feel free to try different options, choose what works for you, and persevere.

1. S. Powell, The Australian, 14 September 2018. From Water Fasting to ProLon: which diet works best.

2. S. Powell, The Australian, 14 September 2018. Diet: 5:2 Works for Type 2 Diabetics in Adelaide Trial.

3. Barnosky, A. R., Hoddy, K. K., Unterman, T. G., & Varady, K. A. (2014). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Translational Research, 164(4), 302-311.

4. Klempel, M. C., Kroeger, C. M., Bhutani, S., Trepanowski, J. F., & Varady, K. A. (2012). Intermittent fasting combined with calorie restriction is effective for weight loss and cardio-protection in obese women. Nutrition journal, 11(1), 98.

5. Varady, K. A. (2011). Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss?. Obesity reviews, 12(7), e593-e601.

6. Harvie, M. N., Pegington, M., Mattson, M. P., Frystyk, J., Dillon, B., Evans, G., ... & Son, T. G. (2011). The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. International journal of obesity, 35(5), 714.

7. Seimon, R. V., Roekenes, J. A., Zibellini, J., Zhu, B., Gibson, A. A., Hills, A. P., ... & Sainsbury, A. (2015). Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials. Molecular and cellular endocrinology, 418, 153-172.

8. Roman, Y. M., Dominguez, M. C., Easow, T. M., Pasupuleti, V., White, C. M., & Hernandez, A. V. (2018). Effects of intermittent versus continuous dieting on weight and body composition in obese and overweight people: a systematic review and meta-analysis of randomized controlled trials. International Journal of Obesity, 1.

9. Headland, M. L., Clifton, P. M., & Keogh, J. B. (2018). Effect of intermittent compared to continuous energy restriction on weight loss and weight maintenance after 12 months in healthy overweight or obese adults. International Journal of Obesity, 1.