The fast diet is named for fasting, not because it is a particularly speedy way to lose weight. It may also be known as the 5:2 intermittent fasting diet, as it involves having 5 days of regular eating, with 2 days a week of extremely calorie-restricted fasting.

For the 5 ‘regular’ days, there are no restrictions. No calorie controls and no foods are off the table. These days should just be treated as usual, though you should avoid going overboard. The main basis of this diet are those 2 fasting days - these days restrict you to eating a very limited amount of food. 500 calories for women and 600 for men.

Protein, fruit and vegetables are the recommended foods for these fasting days, as you will want to get as much nutrition as you can out of such a small amount of calories.

If you can follow this diet, it typically results in weight loss, with some studies saying as much as 12 pounds in 8 weeks. The diet’s creators also noted that it was easy to avoid overeating on non-fasting days by having the fasting days as non-consecutive.

Some conditions may make this diet dangerous, however, and you should speak with your doctor before beginning a fasting diet. Anyone who is underweight or pregnant should avoid it, as well as anyone with a history of eating disorders or diabetes.