Dr Michael Mosley’s guide to the 5:2 diet

Discover more about the 5:2 and Fast 800 diets from the creator himself, Dr Michael Mosley.

Updated on12th July 2022 at 2.05pm

If you're unhappy with your weight for whatever reason, you might consider starting a diet to help shed some pounds.

One of the most popular diets amongst the plethora of different options available is the 5:2 diet, now better known as the Fast 800.

We got the lowdown from the creator himself, Dr Michael Mosley to help you decide if it's the diet for you.

What is the 5:2 diet?

When I came up with the original 5:2 diet in 2012 (where dieters ate restricted calories — 600 for men or 500 for women — for two days a week), intermittent fasting was a radical idea, but one that really resonated.

The Fast Diet rapidly became an international bestseller, translated into more than 40 languages. The diet was embraced by a wide range of people, including doctors, politicians, celebrities and Nobel Prize winners. People found it effective but it was clearly not the final word.

However, in the six years since, there’s been a lot of new scientific research into intermittent fasting and weight loss. I’ve also received a tremendous amount of useful feedback from people who’ve tried the 5:2. So, I decided to put it all together and create something easier and more effective - The Fast 800 diet. The Fast 800 diet incorporates the principles of the 5:2 but we call it ‘the new 5:2’.

The one thing that become increasingly clear to me is that 800 calories appears to be a ‘magic’ number when it comes to weight loss. Eight hundred calories a day may not sound like much but if you choose the right foods then 800 calories can be tasty and filling and will help you lose weight quickly and safely.

In short, the Fast 800 diet recommends doing two weeks of sticking to 800 calories a day, every day, to kick-start your weight loss.

How to do the Fast 800 diet that incorporates ‘the new 5:2’

The Fast 800 (The new 5:2) is based on the ethos of intermittent fasting, time restricted eating and the Mediterranean diet. It includes three separate phases, that you can shift in and out of, depending on how much weight you need to lose.

Phase 1

The VERY Fast 800 - for rapid weight loss .

The rapid weight-loss stage of the diet involves eating 800 calories a day. If you decide this approach is for you, we recommend that you stay on this stage for a minimum of 2 weeks, though you can stay on the plan for up to 12 weeks depending on your goals and how much weight you have to lose. To most people, 800 calories doesn’t sound like a lot, and that is why we have based the 800 calorie a day meal plans in the online programme on delicious Mediterranean style diet recipes, which are designed to keep you feeling full and satiated.

The Very Fast 800 involves rapid weight loss. It is also a highly effective way to bring down raised blood sugars (i.e. pre-diabetic or type 2 diabetic). Over the past few years, major studies have shown that following an 800 calorie a day diet is much more effective than going ‘slow and steady’, with a typical weight loss of around 10kg over eight weeks.

Rapid weight loss is also the best-proven way to reverse type 2 diabetes and prevent people with pre-diabetes from becoming diabetic.

Because The Very Fast 800 is an intensive approach to weight loss, it is not suited to everybody. As with any diet, you should speak to your usual health professional before commencing The Very Fast 800 approach. If you find that this approach isn’t for you, you can skip straight ahead to The New 5:2 plan or the Way of Life.

Phase 2

The NEW 5:2 - sustainable intermittent fasting

Intermittent fasting is a highly effective way not just to lose weight, but to build a healthier, brain and body. This is why, after you have completed the Very Fast 800 stage, I recommend The New 5:2. Instead of keeping to 800 calories per day every day, you schedule two days a week as 800-calorie ‘fasting days’ and follow a healthy Mediterranean-style diet for the rest of the week. You can also jump straight to The New 5:2 if you find that your goals and needs are better suited to this approach.

On your fast days, your body will enter a state of ketosis, just as it would on the Very Fast 800 phase. You will lose visceral fat and achieve a better response to insulin. This, in turn, will make it easier for you to keep to sensible portions during the rest of the week.

If you find that this approach isn’t for you, you can skip straight ahead to the Way of Life plan.

Phase 3

Way of Life – the long-term phase of The Fast 800, The Way of Life phase is a structured, nutritionally balanced guide to eating a healthy Mediterranean-style diet for life.

How you maintain your results on The Fast 800 is very much a personal choice. For most people it is safe to continue with The New 5:2 diet long-term, and many people find that this is an excellent way to stay healthy.

Other people prefer to move onto the Way of Life phase, which doesn’t involve calorie counting, just portion control. People tend to eat the wrong foods because it feels good to do so. When you bite down into a muffin or dive into a packet of crisps, you are responding to carefully designed cues, put in place by food manufacturers, to use food as a defence not just against hunger, but against stress. The Mediterranean-style diet tackles this problem at its root. Based on the diet that has been enjoyed for centuries by people living in and around Southern Europe, it avoids processed foods, is free from added sugar and refined carbohydrates, and instead uses ingredients that have been scientifically proven to make you feel good:

• Healthy fats, especially olive oil, to add flavour and keep you feeling full

• Plenty of protein – again, for flavour and to help you remain full between meals

• Full fat dairy products (in moderation), including cheese

• Probiotics, to promote feel-good gut flora

• Omega-3 oils, to benefit mood and memory

• Fresh fruit and vegetables for their anti-inflammatory and antioxidant effects

What are the health benefits of intermittent fasting?

Short term fasting activates a process within the body called ‘autophagy’ whereby dead, diseased or worn-out cells are broken down, consumed and excreted (autophagy means ‘self-eat’) to make way for the shiny new cells that keep us young.

If following a 5:2 approach, with the incorporation of a lower carb Mediterranean-style diet and two fasting days of only 800 calories, you can expect:

• A greater loss of fat than on a conventional calorie restricted diet

• Reduced inflammation (helpful for rheumatoid arthritis)

• Reduced blood pressure

• Reduced blood sugars and insulin resistance

• A nutritious, high-fibre diet which can improve bowel function

• Possible improvements in brain function and mood

• Bolstered immunity

Can the 5:2 diet reduce type 2 diabetes?

I was diagnosed as a type 2 diabetic in 2013. I was not particularly overweight, weighing about 189lbs (86kgs) and I didn’t look particularly fat, but that was because a lot of the fat I was carrying was internal. I was a TOFI, Thin on the Outside, Fat Inside. Rather than start on medication I went on the 5:2 diet (eat normally 5 days a week, cut your calories to around 600 calories for the other two days), lost 20lbs (9kgs) and reversed my diabetes.

I’m not exceptional. Studies carried out by Professor Roy Taylor and his team at Newcastle University have shown that losing 10-15 per cent of body weight can reverse type 2 diabetes in 84% of recently diagnosed diabetics, and 50 per cent of those who have been diabetic for more than 10 years.

If you are prediabetic, then losing belly fat is also important. Studies by the National Institutes of Health in the US have shown that if you can reduce your weight by just 7 per cent you massively cut your risk of developing diabetes. Even modest weight loss can be helpful, particularly when it is combined with exercise.

What should I eat on fast days?

On your ‘fast’ days, you just need to keep an eye on your calorie intake. You can choose to have either three small meals per day or two larger ones (skipping breakfast or dinner) as long as the total calories add up to 800. There are hundreds of delicious low-calorie recipes and 800 calorie meal plans on our website.

How much weight can you lose on the 5:2?

I’m also urging you to try Time-Restricted Eating (TRE), where you eat within a shorter time window.

Studies also show if you extend your night-time fast to 12 hours or longer, and crunch your eating time into fewer hours, you can reap even more of the health benefits of intermittent fasting.

So, if you start on The Very Fast 800 stage of the program, I advise you eat those calories over a 12-hour window (say between 8am and 8pm) and then go 12 hours without food. Stick to the plan and you could lose up to a stone in three weeks.

But if you decide to do the NEW 5:2 and restrict your 800-calorie days to two days per week, I think it’s a good idea to apply a little extra time-restricted eating, and eat within a ten-hour window (say 8am to 6pm, or 11am to 9pm) on your fast days.

If it seems easier, this can mean skipping breakfast and enjoying two slightly larger meals rather than three small meals.

For the 800-calorie fast days, you can use the low-calorie recipes from the website www.thefast800.com. On other days, you can eat normally but healthily, sticking to a Mediterranean-style diet low in carbohydrates and refined sugars, without having to count calories. On this version of the plan, you could lose 1-2kg a week.

What should I eat on regular days?

Ultimately, it comes down to balance of protein, fibre and healthy fats, which is essentially the Mediterranean Diet. The good news is, whether you incorporate intermittent fasting or not, a low carb Mediterranean Diet has unique power not just to restore your body’s ability to reach its ideal weight and stay there, but also to cut your risk of serious disease. It doesn’t come from a place of restriction but rather it’s about eating more of the right foods. Not only will these foods keep you feeling full, but they also offer important nutrients and health benefits, and taste delicious.

Start the day with eggs: Boiled, poached, scrambled or as an omelette – they’ll keep you feeling fuller for longer compared to cereal or toast. Delicious with greens and parmesan or smoked salmon and a sprinkle of chilli.

Have high-quality proteins: Oily fish, prawns, chicken, turkey, pork, beef and, of course, eggs. Other protein-rich foods include beans, especially edamame beans, dairy and nuts and seeds. Processed meats (bacon, salami, etc) should be eaten sparingly and in small quantities.

Eat more healthy fats and oils: Along with oily fish (salmon, tuna, mackerel), consume more extra virgin olive oil. A splash makes vegetables taste better and improves the absorption of fat-soluble vitamins. Use olive, or coconut oil for cooking.

Eat plenty of different coloured veg: From dark leafy greens to bright-red and yellow capsicum. More variety of colours means more variety of nutrients.

Fibre is good: A low carb Mediterranean diet does not mean no carbs at all. Not only is this very hard to achieve but can be detrimental. This is why complex carbs and fibre are still important and can easily be gained from vegetables, legumes and wholegrains.