Intermittent fasting and the 5 : 2 diet

Intermittent fasting diets, such as the 5:2 diet, are a popular choice among those wishing to lose weight because during non-fasting periods you do not have to give up favourite foods. Some swear by how easy these diets are to follow, others find them impossible to stick to. How much is known about intermittent fasting diets? Can they benefit health, how safe are they and will they work for you?

What is intermittent fasting?

Fasting refers to periods of time when you choose not to eat. It has been used throughout history and across the world for religious and cultural reasons. Over the last six years it has been an increasingly popular way of helping people lose weight. Intermittent fasting (IF) involves alternating fasting periods with periods of normal eating. How long and how frequent these fasting periods are depend on the specific diet followed.

What are the options?

The most well-known include Dr Michael Mosely’s, ‘Fast Diet’ that promotes the 5:2 method. On this diet, you eat normally for five days. Then, on the other two days, you reduce your calorie intake by a quarter i.e. 500 calories if you are a woman and 600, if you are a man.

The Fast 800 programme

In the light of new research Dr Michael Mosely has modified the 5:2 diet, increasing the daily calories on the fasting days to 800 which is low enough to give the metabolic advantages (weight loss, reduced insulin levels etc.) but high enough to be more filling and easier for people to stick to.

16:8 diet

There is also another popular version of this diet known as the 16:8 diet which involves fasting for a 16-hour period every day and restricting eating to an 8 hour window each day. One way of doing this is to miss breakfast and eat between midday and 8pm so you are fasting for 16 hours each day.

Other options are to choose a regular day of the week or month to fast for a full 24 hours.

What are the health benefits of intermittent fasting?

Research has shown that if you stick to this plan you should lose around 1lb (0.46kg) a week if you are a woman and slightly more if you are a man. The success of the diet also depends on not over eating on your non-fasting days.

Studies of intermittent fasting show improvements such as reduced:

• blood pressure
• blood glucose
• cholesterol levels
• inflammation

Intermittent fasting can also lead to improvements in insulin sensitivity and blood glucose control.

One recent study in the British Medical Journal[1] showed patients with Type 2 diabetes could lose weight and reverse their diabetes so they no longer needed to rely on insulin and other medications to control their blood glucose.

What sort of food is best on the fast day?

The best sort of food to eat on a fast day are foods high in protein and fibre as they fill you up for longer. That means fish, lean meat and vegetables.

What food should be eaten on non-fast days?

People following this diet can eat normally however the success of the diet will improve if a Mediterranean type diet is eaten which includes plenty of vegetables, fruit, pulses, fish, olive oil and wholegrains.

Are these diets safe?

These diets are designed for adults. For these diets to be effective the food consumed during the ‘eating windows’ needs to be of high nutritional quality and contain plenty of fruit and vegetables, milk or non-dairy alternatives such as Oat Drink, oily fish, lean meat, nuts and pulses, and starchy wholegrains to provide dietary fibre and all the vitamins and minerals required.

Who should avoid intermittent fasting?

If you are pregnant, breast feeding, have type 1 diabetes, under 18 years of age or elderly you should avoid going without food for long periods of time. Anyone taking medication should check with their GP before embarking on a diet. If you experience dizziness, headaches, or lapses in concentration or any other symptoms you should avoid fasting.

Is intermittent fasting any better than other forms of weight loss?

Studies in humans, almost across the board, have shown that IF is safe and incredibly effective, but really no more effective than any other diet. In addition, many people find it difficult to fast.

So like all weight loss diets it will work if it suits you.

[1] Furmli S, Elmasry R, Ramos M, et al. Therapeutic use of intermittent fasting for people with type 2 diabetes as an alternative to insulin. Case Reports 2018;2018:bcr-2017-221854.