Intermittent fasting (IF) means cycling between periods of eating and fasting. Studies show it can help with weight loss, but in most trials it works about as well as ordinary calorie reduction, because the main effect is eating less overall. It suits some people’s routines and not others. People with diabetes on certain medicines, pregnant women and anyone with a history of eating disorders should not start IF without medical advice.
Common methods
| Method | How it works |
|---|---|
| 16:8 (time-restricted eating) | Eat within an 8-hour window (e.g. 10 a.m.–6 p.m.), fast for 16 hours |
| 14:10 | A gentler version: eat within 10 hours |
| 5:2 | Eat normally 5 days a week; about 500–600 calories on 2 non-consecutive days |
| Alternate-day fasting | Alternate between normal days and very low-calorie days |
Possible benefits
- Weight loss similar to other calorie-reduced diets
- Improved blood sugar and insulin sensitivity in some people
- Simplicity: some people find it easier than counting calories
- May reduce late-night snacking
Claims about longevity and “detox” are not well supported in humans.
Possible downsides
- Hunger, irritability, headaches, poor concentration early on
- Overeating during eating windows
- Difficulty fitting around family meals and social life
- Not suitable for everyone
Who should avoid or get advice first
- People with type 1 diabetes, or type 2 diabetes on insulin or sulfonylureas (hypoglycaemia risk)
- Pregnant or breastfeeding women
- Anyone with a current or past eating disorder
- Children and teenagers
- People with low body weight or frailty
- People taking medicines that must be taken with food
Tips if you try it
- Start with 12–14 hours overnight, then extend if comfortable
- Stay hydrated; water, black coffee and plain tea are usually allowed during fasts
- Prioritise protein, vegetables and whole grains in your eating window
- Don’t use the eating window as an excuse for ultra-processed foods
- Stop if you feel unwell, dizzy or develop an unhealthy relationship with food
Shift workers and nurses
Rotating shifts make fixed eating windows hard. Some nurses choose a window that matches their shift, but avoid long fasts during demanding shifts where low blood sugar could affect safety.
Frequently asked questions
Is intermittent fasting better than a normal diet?
For weight loss, research generally shows similar results. The best diet is one you can sustain.
Related reading: Healthy eating on 12-hour shifts · Weight-loss injections explained
Updated 5 November 2026. Speak to your doctor before major diet changes if you have health conditions.