Intermittent fasting is a method of dieting that restricts the amount of time you are allowed to eat. The appeal of these diets is that you don’t need to count calories or eat certain foods. But there are so many versions, it’s hard to know which one is best. Here’s what the research says.
The 5:2 diet
This is a popular version of intermittent fasting where you eat a very low calorie diet (about 500kcal) for two days each week (any two days). On the other five days, you eat as normal.
Research has shown that it’s possible to lose weight with this diet; it also improves several markers of health, such as reducing levels of glucose and cholesterol in the blood.
But the 5:2
diet is unlikely to be more effective for weight loss than traditional methods of dieting. This is because 5:2 reduces calorie intake to a similar extent as traditional dieting.
There is some evidence that conducting the two days of very low calorie intake on consecutive days can improve insulin sensitivity – a risk marker for type 2 diabetes – to a greater extent than traditional dieting. This approach also leads to decreases in blood lipids (fatty substances found in the blood) compared with traditional dieting.
An important extra benefit of 5:2 is that you can consume some food during the “fasting” period, providing an opportunity to take in vital nutrients.
Dieting often leads to losses in muscle and bone mass, alongside fat mass because consuming a balanced diet while reducing calorie intake is difficult.
This can compromise long-term weight loss efforts as muscle is more metabolically active (burns more calories) than fat. Eating enough protein can help to reduce the loss of muscle mass while dieting, with a bonus of reducing appetite.