What is the 5:2 diet?

The 5:2 diet is a popular intermittent energy restriction method of weight management. Intermittent fasting, has been associated with a plethora of proposed health benefits from weight loss to blood sugar balance, reduced inflammation to improved brain function.

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Published in The Fast Diet book by Dr Michael Mosley in January 2013, it promotes eating what you want for five days of the week, then dramatically cutting calories for the other two. This part-time dieting approach focuses more on how you eat than what you eat.

Visit our ‘All you need to know about diets’ page for recipes and more expert advice on weight loss, including low-GI and the Mediterranean diet’

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How does the 5:2 diet work?

The theory behind the diet is that after a period of hours with limited calories, the body switches from the ready supply of energy from food to burning its fat stores. Its simplicity, and the fact you can eat pretty much what you like five days of the week, are key to the 5:2 diet’s popularity. Dieters are recommended to consume a ‘normal’ number of calories for five days and then, for two, non-consecutive days, eat just 25 per cent of their usual calorie total – 500 calories for women and 600 for men.

How to follow the 5:2 diet?

There are no restrictions on the types of food you can eat, however a balanced diet is emphasised and it’s suggested that women, following the diet, may expect to lose about 1lb a week, with men losing about the same or a little more.

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When you’re following any low-calorie diet, it’s important to make every calorie work – this means choosing nutrient-dense foods. Although you might think it’s easier to resort to calorie-counted ready-meals, you’d be better opting for lean protein like poultry and vegetables. When following the diet, make sure that your non-fast days are packed with nutritious options, including fruit, veg, wholegrains and protein such as chicken, fish, turkey and dairy foods.

Maintaining your hydration with water and herbal teas is important because dehydration can be a cause of headaches and tiredness. Some followers choose to ease into fasting by initially extending the time between their evening meal and the first meal the next day with a minimum gap of 12 hours.

Avoid fasting on two consecutive days – instead break your week up, for example, by fasting on Monday and Thursday – this helps prevent tiredness.

What’s the evidence for the 5:2 diet?

Studies suggest that daily calorie restriction intermittent fasts, such as the 5:2 diet, are as effective at promoting weight loss in those who are overweight and obese as alternate days.

The results you achieve will vary, however, and be dependent on your individual circumstances and the amount of weight you have to lose. You may also need to be careful that you don’t over compensate on non-fast days.

In addition to weight loss, the 5:2 diet, and similar intermittent-fasting regimes, claim that calorie restriction may also be linked with:

More evidence is coming to light regarding the benefits of this type of diet, although, there is clearly a need for longer term, human-based studies.

Anonymous female dining healthy vegan plant-based salad in bowl with avocado, cashew, micro-greens, pok choi, chickpeas, tomato, lettuce, cucumber, sesame. Flexitarian fatty acids and dietary fiber

Do 5:2 diets work?

The 5:2 and similar intermittent-fasting diets are said to be easier to follow than traditional calorie restriction, one major advantage being that you do not have to exclude any food groups and you can choose what you want to eat.

Studies suggest that the 5:2 diet is as effective as calorie restriction for weight loss and may offer some additional benefits such as improvements in fasting blood sugar and appetite management.

Is the 5:2 diet healthy? Our nutritionist’s view...

Fasting is a simple concept that appears to promote weight loss, although the hunger experienced by some, may be a limiting factor. Many followers see the eating regime as less of a 'diet' and more of a way of life that can help them maintain their weight loss in the longer term. Nevertheless, fasting is a personal experience and some report feeling low in energy, having poor concentration and experiencing headaches and dizziness on fasting days.

Much of the emphasis given to the 5:2 is on the ‘fasting’ days, but in order to be safe, effective and healthy, the food consumed during the other five days of the week needs to be of high nutritional value. For this reason, you should aim to include essential fats from oily fish, nuts and seeds, lean sources of protein, wholegrains and starchy carbs with plenty of fruit and vegetables to supply the necessary fibre, vitamins and minerals that you need. If you intend to follow it for longer, you may need to consult a dietician to ensure you’re not at risk of nutrient deficiencies.

Who should not follow a 5:2 diet?

As with all diets, pregnant and breastfeeding women as well as diabetics on medication, should seek medical advice before embarking on a restricted eating programme. Furthermore, this sort of diet may be unsafe for teenagers and children, who are likely to miss out on crucial nutrients needed for growth, these groups may also be at risk of developing unhealthy eating habits. Furthermore, if you have or are recovering from an eating disorder this diet may be inappropriate for you.

Those on medication, especially if it needs to be taken with food at set times, should seek advice from their GP prior to commencing the diet.

Please note, if you are considering attempting any form of diet, please consult your GP first to ensure you can do so without risk to health.

You may have read that emerging evidence is suggesting a beneficial role of fasting diets for the control and management of type 2 diabetes, however, refer to your GP if you have diabetes or have any other long-term health condition.

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This article was reviewed on 13 October 2023 by Kerry Torrens

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