The Fast 800 has been designed as a flexible plan to help anyone based on their aims – whether you have a lot of weight to lose and want to lose it fast, or just a little to lose from around your middle.

Most important is to make sure it is sustainable – this is why when completing the Fast 800 we recommend you complete it in stages – moving to a way of eating that works best for you. It is also why the food focuses on flavour and is so delicious.

The Fast 800 can involve several stages, from rapid weight loss at the beginning, through to sustainable intermittent fasting, depending on your goals and current weight.

Stage 1: The Very Fast 800 – Rapid weight loss

For those with a lot of weight to lose, you can begin with the Rapid Weight Loss stage of the diet. This involves 800 calories a day.

We suggest you stay on this stage for a minimum of two weeks, but you can stay on it for anything up to 12 weeks, depending on your circumstances and how much weight you have to lose.

How to do it?

To make up your 800 calories, you can either rely on real food or make use of shakes to replace some of your meals. You can find out more about the food recommended here. Shakes should be low in sugar, high in fibre, and contain essential protein, fats, vitamins and minerals. Because they are low in carbs and calories they will induce mild ketosis, which will reduce hunger and help preserve your muscle. You can find out more about shakes here.

As your body switches from burning sugar to burning fat you may get headaches or become light-headed. These symptoms are likely to be due to dehydration which is why it is so important to drink extra water. The normal advice is 8 cups a day, or about 2 litres. Another way of telling is by the colour of your pee. Clear or pale yellow means you’re all set. Darker means you need to drink up.
As well as cutting down to 800 calories a day, you can add in a Time Restricted Eating (TRE) programme. This means, from the start, aiming for a 12-hour overnight fast.

The very Fast 800 is not for everyone however, you can find out more about who should and should not do this here. If you do not have much weight to lose, or find it is not for you – move straight on to step 2.

Stage 2: The New 5:2 – Sustainable intermittent fasting

At some point, it may be at the end of the first two weeks or it may be later (depending on how you get on), you are going to want to switch from the Rapid Weight Loss phase to something which is more gradual and sustainable.

This means switching from 800 calories every day to intermittent fasting, where you will be on 800 calories for a few days a week

How to do it?

Intermittent fasting involves restricting calories to 800 a day on fasting days, then eating a healthy lower carb Mediterranean diet for the rest of the time. This can be much more sustainable and enjoyable than constant calorie restriction, as much of the evidence points at daily calorie counting failing to be sustainable in the long run.

On the days when you are not fasting, you don’t have to count calories, though you will need to be careful about portion control and maintain a healthy Mediterranean-style diet, which the online course will help you do using the meal plans and recipes

Try the 5:2 diet initially, 5 days without calorie counting, eating a balanced Mediterranean style diet and then 2 days counting calories.

At this stage try extending your overnight fast by reducing your TRE window from 12 hours to 10 hours. In other words, making your overnight fast last 14 hours. The reason for doing this is that it will help maintain and enhance the benefits of intermittent fasting, in particular autophagy and ketosis.

Stage 3: Maintenance – a way of life

Once you’ve achieved your goals it will be time to go on to the Maintenance Phase. This will be another hugely important moment, a time when you consolidate all the things you have learned, but also a time where you might be tempted to go back to your previous habits. The course is designed to prepare you for that moment. The good news is that the longer you stick to the maintenance programme, the easier and more natural it becomes.

The more you try it, the more you will find what works for you, and it is flexible enough to deal with wherever you are on your healthy living plan. Feel the weight creeping up again? Try returning to intermittent fasting. Find the Very Fast 800 to hard to achieve? Give intermittent fasting and the 5:2 a go.

As with any diet, always make sure to discuss it with your healthcare professional – especially if doing the Very Fast 800 as it can be intense and have a rapid impact on your blood sugars. For help with this conversation please feel free to use our handout here.

Getting Active

Insulin resistance, which leads to raging hunger and all sorts of problems including raised blood sugar levels, often starts with inactivity. If you don’t use your muscles enough, then over time, fat builds up inside the muscle fibres and insulin resistance develops. The best way to reverse this is to get more active.

Sit less, move more

You can start by sitting less. If you spend a lot of time sitting continuously (and many of us sit for over 8 hours a day) then the sugar and fat that you eat will just sit around in your arteries causing problems, rather than being dumped in your muscles where they will get burnt as fuels. So set an alarm and try to stand up and walk around for a few minutes every 30 minutes.

Take short, brisk walks

Walking is also a great way to reduce insulin resistance and keep hunger at bay. The important thing is to make your walking brisk. One of the most effective ways to get the maximum benefits is to do something called Active 10. This involves aiming at doing 3×10 minutes of brisk walking a day. You can find more details at www.nhs.uk/oneyou/active10/home.

One of the best ways to keep yourself motivated is to get into a friendly competition with someone else. You will find your own ways to get more activity into your life, but they could include deciding to always take the stairs, parking further away from the supermarket or joining a walking club.

High Intensity

The greatest benefit comes from occasionally pushing yourself, getting your heart rate up. This can be done while walking, running, swimming or on a bike. The idea is that you go as hard as you can for short bursts, no longer than 20 seconds, just enough to get your heart rate going.

With any exercise regime it is important that you do this properly and build up gradually.

Check with your doctor first if you have a heart problem or are very inactive.


The content on the Fast 800 is meant to be informative in nature, but it shouldn’t take the place of qualified medical advice. If you’re looking to make a significant change to your diet and training regimen please consult your medical professional first.

For more information on who should not do this diet, please find out more here.