Is intermittent fasting bad for you? These are the benefits and drawbacks of restrictive diets - and the healthiest way to lose weight explained

Lots of different diets come under the intermittent fasting umbrella, like the 5:2 diet, the 16:8 method and Eat-Stop-Eat

The diet has become very popular in recent years, however there is evidence that shows it might not be the best weight loss method (Photo: Shutterstock)
The diet has become very popular in recent years, however there is evidence that shows it might not be the best weight loss method (Photo: Shutterstock)

Intermittent fasting has become one of the most popular diets in recent years, with celebrities like Terry Crews, Jennifer Aniston and Chris Pratt all swearing by it.

But what exactly is intermittent fasting - and does it really work for weight loss?

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This is everything you need to know about the diet, from the 5:2 method to the Eat-Stop-Eat diet.

What is intermittent fasting?

Intermittent fasting is a type of diet that cycles between periods of eating and periods of fasting.

There are a few diets within the intermittent fasting category, such as:

- The 16:8 method, which involves participants restricting their eating times to only eight hours a day, such as between 12pm and 8pm, and is then followed by 16 hours of fasting

- Eat-Stop-Eat, which involves fasting for 24 hours one or twice a week - for example, by not eating dinner one day until dinner the next day

- The 5:2 diet, which involves eating normally for five days of the week, and then consuming only 500 - 600 calories on two non-consecutive days

Does intermittent fasting help you lose weight?

There have been many studies done on the effects of intermittent fasting, with some showing positive results and others showing that the diet doesn’t have many benefits.

One of the most recent and most rigorous studies into intermittent fasting, which was published in JAMA Internal Medicine, found that adults who stuck to a 16:8 diet, only eating all of their meals between 12pm and 6pm, gained almost no benefit from it.

The study found that those on this diet, known as the 16:8 diet, lost on average between two to three and a half pounds over the three month study period, and most of the weight lost was not from body fat but “lean mass”, which includes muscle.

Ethan Weiss, a cardiologist at the University of California and one of the co-authors of the study, said: “You don’t want to lose lean mass. You want to lose fat mass. Here we found that two-thirds of weight loss came from lean mass.”

In the findings portion of the study, researchers wrote: “In this prospective randomized clinical trial that included 116 adults with overweight or obesity, time-restricted eating was associated with a modest decrease (1.17%) in weight that was not significantly different from the decrease in the control group (0.75%).”

The study said that “time-restricted eating, in the absence of other interventions, is not more effective in weight loss than eating throughout the day”.

Niamh Hennessy, lead dietitian at Bupa Cromwell Hospital, says that instead of intermittent fasting, “making small changes to your eating habits, largely by cutting out food high in saturated fat and sugar, is the best way to eat well and maintain a healthy weight”.

She explains that many people who follow a set diet or eating plan end up putting the weight back on, and that intermittent fasting is “no exception”.

How can I safely lose weight?

The NHS has a free 12 week diet and exercise plan, which you can access as an app, called NHS Weight Loss Plan, on either the Apple app store, or the Google Play store.

Alternatively, you can download the plan in PDF form from the NHS website.

“The plan, which has been downloaded more than seven million times, is designed to help you lose weight safely - and keep it off,” the NHS explains.

The plan itself features guides to safe and sustainable weight loss, advice on healthier food choices and exercise routines to follow.

It is designed to help people lose weight at a safe rate of “0.5kg to 1kg (1lb to 2lb) each week by sticking to a daily calorie allowance”.

The plan is intended for adults with a body mass index of 25 and over - it is not suitable for children, young people or pregnant women.

If you have a medical condition, you should consult your GP prior to starting any weight loss programmes.