Running and the 5:2 diet

How does running work with the 5:2 fasting diet? Is it safe and how much can you run while fasting?

Running and the 5:2 diet

It’s been several years since we first heard of the 5:2 phenomenon. The idea of fasting for two days out of seven may originally have seemed like yet another fad diet to many of us. However, the Fast Diet seems to be sticking around for the foreseeable future.

But how does it work for runners? Is it possible to fast and run? How much running can you do on this diet and how should you plan your training schedule when fasting?

The ancient benefits of fasting

Fasting has been around for thousands of years and has been found in many different cultures including Greece, India, and historically it has been an element used in almost all religions.

Hippocrates and Plato believed in the power of fasting, and Mark Twain is quoted as saying, “A little starvation can really do more for the average sick man than can the best medicines and the best doctors”.

Research suggests there are major health benefits to intermittent caloric restriction. The main benefits include reduced risks of cancer, cardiovascular diseases, diabetes, insulin resistance, immune disorders, a reduction in cholesterol and more generally, the slowing of the ageing process, and the potential to increase maximum life span.

Fasting becomes the Fast Diet

Journalist and TV presenter Dr Michael Mosley made some surprising discoveries about these benefits in 2012-2013, when looking for a way to prolong life and stay younger, using himself as the guinea pig. He was making a documentary for the BBC, the result was Eat, Fast and Live Longer, in which he discovered the health benefits of fasting.

After experimenting with fasting for different periods, and calorie restricted diets, he found that two days a week of a 600 calorie intake (adjusted to 500 calories per day for women) allowed the body to repair itself while impacting his life (and his love of food) as little as possible. A side effect of this was losing excess weight, and this 5:2 rhythm of fasting days was then marketed as a weight loss diet.

Running and fasting

If you’re a regular runner and are looking to lose weight without making massive lifestyle changes or cutting out food groups completely, you may well be able to make the 5:2 diet work for you. It has been tried out by a fair few runners, some find it excellent way to shift those final few pounds, while some find it harder to balance training and fasting.

We asked you bugs in a poll if you thought the 5:2 diet was a healthy way to lose weight. The results are in: 52 per cent of you said you thought it was. So the Fast Diet is a winner among runners, if by a narrow margin.

Fasting as a training tool

Dr Mosley says, “There is good evidence that people who exercise in the fasted state burn more fat. In one study men who exercised before breakfast burnt more fat than those who exercised afterwards.” We know that running ‘on empty’ first thing in the morning can be a useful tool to help teach the body to use fat as its primary fuel source, something that it will need to do when running for long periods, such as during a marathon. Fasted training can help marathon runners avoid hitting the wall on race day.

Just make sure you plan to take on a percentage of your allowed calories soon after your run, and don’t push yourself too hard. “Don’t attempt to do a lot of endurance training on a fasting day and if you feel uncomfortable, stop,” advises Dr Mosley.

Organising your fasting around your training

Fast on your rest days whenever possible. If you’re doing two days of fasting per week, you should be able to organise these around your running schedule without too much difficulty, for all but the most intense training plans (when dieting is probably not necessary anyway!).

You may actually find that exercise is a welcome distraction on fast days, but try to ensure that if you run on fast days, you schedule your easiest, shortest sessions on these days. Stop if you feel light-headed.

Try some yoga or Pilates, go to a fitness class, do some stretching or go for a brisk walk if you don’t have the energy to run. However, up to 45 minutes of light to moderate effort shouldn’t pose too many problems. If you are running intensively, or working out for more than an hour you will probably struggle.

Running may well actually feel harder the day after a fast day, as you have very little glycogen stored in your muscles, so experiment and adapt your programme to the way that works best for you. The day after a fast, try having a high-carb breakfast such as porridge, toast or a banana at least an hour before you run.

Nutritious calories    

If your calorie intake is limited to 500 or 600 calories, it’s more important than ever that you are getting them from whole, nutritious foods.

Aim to make sure your meals include eggs, nuts, beans and pulses, lean meat and fish, and plenty of vegetables. Vary your meals too. If you’re grabbing food on the go, buy something which has the calories displayed on the packaging so you know what you’re eating.


As ever, it’s important to stay hydrated when running. And when fasting, you’ll need to drink more water than usual, as the body is used to getting around 20 per cent of all water intake from our food. Drink regularly throughout the day.

Adapt if necessary

The 500/600 calorie restriction should be used as a guide, if you are doing a lot of exercise, don’t beat yourself up about adding in a few extra calories. You will know if you’re really cheating or not!

If you are aiming for a particular target weight, once you have reached your goal weight, you can switch to 6:1, in other words fasting for just one day a week in order to maintain your target weight and still get the health benefits of fasting.

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