How The 5:2 Diet Could Be Tricking You

How The 5:2 Diet Could Be Tricking You

The “new” weight-loss strategy known as the 5:2 diet has been receiving much attention in the media since the book The Fast Diet: The Secret of Intermittent Fasting – Lose Weight, Stay Healthy, Live Longer was launched late last year. But does it really work? Surinder Baines examines the evidence.

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The 5:2 diet allows you to eat as usual for five days and to fast for two days. On fasting days, the dieters need to restrict intake of food to approximately 2000 kilojoules (500 calories) a day for women or 2400 kilojoules (600 calories) for men.

The two days of fasting don’t have to be consecutive and you can decide how you want to spread your food intake on those days as long as you adhere to energy restriction. The food consumed during the two fasting days should have little fat and carbohydrate content and alcohol consumption is not recommended.

During the two fasting days, you are typically allowed protein foods such as eggs, or low-fat yoghurt or cheese for breakfast and protein foods such as chicken, fish, lean meat, along with salad or other non-starchy vegetables for lunch or dinner. You are permitted water, green tea, or black coffee. While you can have milk with your beverages, it must be counted toward your caloric intake.

Not a fad?

Intermittent fasting or restricting energy intake for weight loss, which is what the diet is based on, is not a new concept. And there are other kinds of fasting diets around, such as “alternate day fasting”. But while energy restriction in the form of various weight-loss diets has been investigated in both humans and animals, there’s little research regarding the utility of intermittent fasting in humans.

A 2011 study in the United Kingdom that investigated the effects of intermittent energy restriction (to approximately 2266kJ a day for two days) compared to continuous energy restriction (approximately 6276KkJ a day for seven days a week) over six months, in 107 young overweight or obese women. It reported that both diets were equally effective for weight loss, as well as other markers of good health.

But there seemed to be potential difficulties in adherence. At the completion of the study, only 58 per cent of the women in the intermittent fasting group planned to continue with the diet, compared to 85 per cent of those in the energy-restricted group.

This study was one of the largest undertaken in this area so far and the few previous studies in the field have had a much smaller number of participants. Although these smaller studies have been conducted for shorter time periods, the UK study is also considered to be relatively short term.

Weight loss within the first six months is common with a lot of different types of diets. But research studies have shown that the majority of people put much of the weight back on within three to five years.

Need for caution

Many people who have tried the 5:2 diet report that they have been successful in losing weight but this is the case for most weight-loss diets in the short term. The issue of long-term compliance with the two days of energy restriction remains unresolved, as does long-term weight maintenance because people usually are not able to keep to their new weight.

Difficulties in adherence resulting in weight regain may encourage some people to try another dieting attempt and this can lead to the cycle of weight loss and weight regain being repeated. This happens in most cases of dieting-related weight loss.

The risks or the potential to overeat or gorge on non-fasting days also needs to be investigated. Diet quality is of particular significance for those who fast intermittently to ensure that all nutritional requirements are met and that the intake of some nutrients that have low intakes anyway (such as calcium) is not further compromised.

What’s more, we still need to investigate whether intermittent fasting is a safe weight-loss strategy, especially for people with diseases such as diabetes. Starvation-type diets have side-effects such as dehydration, anxiety, irritability, tiredness and lethargy and whether we should be looking out for these in the 5:2 diet remains to be determined.

Intermittent fasting is reported to be effective among those who have used it for weight loss and it seems to be as effective as an energy-restricted diet in the short term. It may be a viable weight-loss option for some people but we need to research its effects beyond those reported, especially since many of these effects are anecdotal at present.

It’s best to follow healthy eating dietary guidelines and seek advice from your doctor before embarking on intermittent fasting as a weight-loss strategy.

Surinder Baines is Associate Professor in Nutrition and Dietetics at University of Newcastle. She does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations. The ConversationThis article was originally published at The Conversation. Read the original article.


  • Been on the warrior/Waterbury diet for 4-5 months. 20 hour fast, 4 hour eating. It’s working well- lost nearly 10kgs, I eat till I’m satisfied at the end of the day. During the day it’s either a few almonds, berries or some fat free, sugar free yogurt. BCAAs for breakfast and lunch to prevent muscle loss. I also eat a little bit more on training days.

  • I have been on the 5:2 diet for 7 weeks and it has been fantastic. I lose about 0.5 kg per week, and it is just not that hard. I have had difficulties with my weight for more than ten years and this just seems too easy. I am hoping in about six months I will have lost enough weight to get to my correct BMI then I can go on 6:1 just one day a week for the rest of my life which I think will be a breeze. This is the simplest diet ever.

    • I completely agree with you Greg. Have been on diet for 4 month now and have lost 10 kgs. I find it very simple and I’m not that strict on it. I only do it now every other week, but may try the 6:1 later in the year.

  • I’m 35 kilo’s down from my peak weight last year.

    None of this fad-diet stuff, no calorie counting, not even excessive exercise – just watching portion size, that’s all it was, end of the day.

  • Amazing – different diets work for different people! There must be an academic paper in this somewhere.

  • Dr. Michael Mosley’s 5:2 diet and book may be recent, but people have been advocating different types of intermittent fasting for many years. It is pretty evident that traditional everyday calorie restriction diets also lead to regaining weight after the diet ends and have not slowed the growing global obesity problem. With restaurant portion sizes growing and increased access to high-calorie, low-cost food, people will overeat regularly, not just if they are on a diet or fasted the day before. I alternate day fast and have lost over 20 lbs in 2.5 months without other lifestyle changes. It teaches people about the calories in food, portion control, and self-discipline without feeling deprived daily.

  • Surinder, there’s another much easier version of intermittent fasting which works very well. Instead of 5:2, you fast every day by only eating over an 8 hour period during the day, and then fasting for the remaining 16 hours (including sleep time). Doing this every day is much easier and doesn’t create nearly as much stress. I start my day with juice followed by a coffee, and then at around 11.30am have my first meal – breakfast / brunch, followed by another coffee. This keeps me going until mid-afternoon, when I might have a light snack followed by a normal dinner sometime before 7.30pm. I have found that I’ve effectively reduced my food intake to the equivalent of 2 full meals a day, and have lost around 9 kilos in about 5 months. By changing my daily routine, it has quickly become an easy habit to maintain.

  • My takeaway here is that those with serious illness such as diabetes should not attempt a “starvation” diet (and I would argue that those with serious illness should not undertake ANY diet except under strict medical supervision, and would also argue that this form of intermittent fasting hardly qualifies as “starvation”). The article also casts about as to what MIGHT happen: PERHAPS people will gorge themselves on the days of unrestricted eating (preliminary anecdotal evidence so far seems to indicate that this is not what’s happening); MAYBE some people will not adhere to the diet longterm, etc., which is true of virtually every diet ever conceived (thus the 95-98% failure rate of diets over a long period of time).

    There simply aren’t yet enough long-term studies to do much other than speculate, as this writer has done. For now one must analyze the short-term studies and review anecdotal evidence, while longer studies are undertaken. I find the title of the article to be a gimmicky come-on with very little in the way of facts to justify it.

  • It’s a good article with a balanced view- I see so little of this in the UK media, everybody seems to just praise this fad. It CAN be very dangerous, especially in some cases- and I am living proof. I just wrote about it on my blog – in short, don’t attempt if you ever had eating disorders, falling back into anorexia or bulimia is just around the corner

  • Surinder Baines’s opinion seems clearly to be based not solely on education (extensive I’ll wager and shifting as knowledge is regularly superceded by fact) yet on the potential troubles affiliated with being a completely mindless carb swilling moronic twit. It seems the thought is that people (poor uneducated cretins) must surely gorge upon sausages and pressed cheese for 5 days, then eat a bowlfull of beef jerky and a packet of crisps on fast days. Those who struggle with the weight loss merry-go-round whilst living fully occupied lives will surely welcome the benefits , both health and physicality, of a way of eating which is more readily sustainable than just grabbing whatever one can when one passes the fridge everyday or driving past mcdonald’s drive thru or applying some heat to a supermarket processed tin of slop on toast in starving desperation. give us a little more credit than that some of us are very well researched laypeople

  • I am not saying this is be mean-spirited. The diet’s working fine for me and my husband. I don’t know why people either don’t read, listen, or watch, but there is a clear verbal and written warning that the diet’s not for anorexics, bullimics, diabetics, or pregnant, etc. people, but people do what they do anyway and then complain. You don’t like the diet, then use something else or nothing. Complaining about it is just as irritating as as not losing weight when you’re on a diet. Read people, listen, and learn. The reason people re-gain the weight is because they treat it as a diet. You will regain weight if you resume your old eating habits, which got you in trouble in the first place. This is supposed to be a LIFE CHANGING PROGRAM, not a temporary solution. Blame yourself if you re-gain, not the program.

  • I have IBS and am a coeliac (great combination LOL), and been prescribed Nexium as well. Anyway, when Womans Day published the 5:2 Diet with about 12 days of recipes, I thought I would give it a go. One to help my tummy issues, but also to lose a little weight. I decided to do a Monday and Thursday. The first Monday was a tuffy. I don’t normally eat a LOT, but knowing you cant eat much seems to make you hungrier LOL. The first day I did most calories in the morning lunch which left minimal for dinner (boy did I enjoy dinner though even though I could just have berries and yoghurt). But I pushed through it, drinking lots of water and ginger/lemon tea. I find it really easy now. I found recipes that I actually like that I can mix and match with calorie count already done so there is no work for me. It may seem minimal quantities but when you cook it up, its actually quite filling. I cook my lunch up the night before so I am not struggling in the morning. For example for breaky I have quinoa with grated apple, sultanas, yoghurt and sliced strawberries; lunch is chicken thigh, onion, with cumin, paprika, chilli flakes with couscous and sliced cucumber; and dinner is some penne pasta with pancetta, zucchini, onion and ricotta stirred through. Cant complain about that!!! Yes the serving sizes are small but probably no smaller than you should eat anyway. Crikey I tried the Kale, mushroom and tomatoes on a slice of toast for breaky and it took up the whole plate…couldn’t eat it all. Anyway, it works for me and knowing that its only a day is great. Even though I think about all I can eat the next day, I find that I actually DONT eat as much as I thought I would. Yes, it works, but you have to have a little willpower as well, which can be said of a lot of things 😉 I agree with etherial, I don’t treat it as a “diet” but rather a way of helping my body with diet and exercise rather than medicating it and it seems to be working.

  • I have being on this diet for 3 months now. it is easy to follow. However, I lost 1 kg the first 2 weeks and only 1 kg after that (total 2 kg in 3 months), which is great, but it will take me a LONG time to get to a normal weight!

  • I have lost 7 kilos in four months. Now am getting colic pains day after fast which are unbearable….anyone else suffering this?

  • From what I understand from the research on fasting, fasting diets are different to every day caloric restriction because of the effect of fasting itself on health. Periods of fasting have unique benefits besides just weight loss, one of the interest effects is on overal levels of insulin growth factor 1, and cell metabolism

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