Intermittent fasting means limiting eating to certain times of the day or week. It has become one of the most popular ways to lose weight. Here’s what the evidence says and who it suits.
Common types
- Time-restricted eating (such as 16:8): eat within an 8-hour window, for example 11 am to 7 pm, and fast for the other 16 hours.
- 5:2: eat normally on 5 days and about 500 to 600 calories on 2 non-consecutive days.
- Alternate-day fasting: alternate normal days with very low calorie days.
Does it work?
Studies show intermittent fasting leads to weight loss, mainly because people eat fewer calories overall. When researchers compare it with ordinary daily calorie cutting, results are generally similar. It isn’t magic, but some people find it easier to follow because there are fewer decisions about food.
Tips if you want to try it
- Start gently, for example with a 12-hour overnight fast, and extend it gradually.
- Drink water, and black coffee or tea, during fasting periods.
- Make meals count: protein, vegetables, whole grains and healthy fats. Eating very large or sugary meals in the eating window cancels out the benefit.
- Keep up activity and sleep.
Possible side effects
Hunger, headaches, tiredness, irritability and difficulty concentrating are common at first and usually ease within a few weeks.
Who should not try it without medical advice
- People with diabetes, especially those taking insulin or sulfonylureas, because of the risk of low blood sugar.
- People who are pregnant or breastfeeding.
- Anyone with a history of an eating disorder.
- Children and teenagers.
- People who take medicines that must be taken with food, or who have a medical condition such as low blood pressure.
The bottom line
Intermittent fasting is one option, not the only one. The best approach is the one you can keep up. If it leaves you feeling unwell or preoccupied with food, stop and try a different approach.
See also: how to lose weight safely and protein for weight loss.
More in our Weight Management guide: all our articles on this topic in one place.
This article is for general information only and isn’t a substitute for advice from a doctor or pharmacist. Always read the label before using any medicine.
