Fad diets come in and out of fashion all the time.

Intermittent fasting is one of the more popular diets around at the moment. Numerous famous faces have at one point sworn by it - from Ben Affleck to Jennifer Aniston.

What is intermittent fasting?

Intermittent fasting involves eating all your food in a restricted window. It's also called 'time-restricted feeding'. Most people fast naturally, by sleeping for eight hours and then eating over the remaining 16 hours of the day. However, intermittent fasting often restricts the eating window even further, to a four or six hour period. The health benefits of intermittent fasting are largely anecdotal - in other words based on personal accounts rather than hard, scientific evidence. Is intermittent fasting for you? Here's what the science says. Intermittent fasting is bad for athletes: Research found that fasting impaired finish times, speed and power output in people undergoing sprint tests. Scientists say this is likely because high-intensity exercise depends on carbs as fuel. Intermittent fasting doesn't work for weight loss: a brand new study from the University of California followed 116 overweight people for 12 weeks. Half restricted their food to a limited time window, the other half ate a normal diet. Scientists say there was no 'statistically significant' difference in weight loss between the two groups.

When does fasting work?

With fasting, food is restricted - so your calorie intake will be much lower. That in itself will likely lead to weight loss. Losing weight is often an overcomplicated process when, in a nutshell, burning off more energy than you take in is a proven way of getting there. By restricting the volume of food you consume, you'll also retrain your body to handle carbs more efficiently. This is known as insulin sensitivity. If you carry a lot of body fat, that probably means your ability to use the sugar from carbs could be controlled a little better.

Who should avoid intermittent fasting?

You don't necessarily need to fast to get into a calorie deficit. However, if it helps you get there, then perhaps give it consideration. If it's not your cup of tea, you can still lose weight by calculating the calories and macros you need, and then basing a sensible meal plan around those figures. Athletes or people with very active lives should probably avoid, as food as needed very regularly in these cases.