1B+
People living with obesity
In 2022 more than 1 billion people worldwide were living with obesity.
Source: WHO / The Lancet 2024
Intermittent fasting
How intermittent fasting works — 16:8, 5:2 and alternate-day — what the research shows, a sample 16:8 schedule, and who should not fast.
Fasting in numbers
16:8
fast 16 hours, eat in an 8-hour window — the most popular method
5:2
eat normally 5 days, about 500–600 kcal on 2 non-consecutive days
Similar
weight loss to everyday calorie cutting in most trials
0 kcal
drinks during the fast: water, black coffee, plain tea
Types of intermittent fasting
16:8 time-restricted eating
For example eat 10am–6pm. Easy to fit around work and often reduces late-night snacking.
5:2 diet
Two low-calorie days a week. Popularised in the UK; needs planning on fast days.
Alternate-day fasting
Very low intake every other day. Harder to stick to long term.
12:12
A gentle start: overnight 12-hour fast, e.g. 7pm–7am.
Sample 16:8 day
| Time | What to have |
|---|---|
| 7am | Water, black coffee or tea |
| 10am | First meal: eggs, wholemeal toast, tomatoes |
| 1:30pm | Lentil or chicken salad with wholegrains |
| 4pm | Yoghurt and berries or a handful of nuts |
| 6pm | Last meal: salmon, vegetables and new potatoes |
| 6pm–10am | Fasting — water and calorie-free drinks only |
Who should not try fasting without medical advice
- Pregnant or breastfeeding women
- People with type 1 diabetes or on insulin / blood-sugar medicines
- Anyone with a history of eating disorders
- Under-18s and older adults who are frail or underweight
Tip
Fasting only works if meals in the eating window are balanced — fill up on protein, vegetables and wholegrains rather than overeating.
World health facts
All facts2.5B
Adults overweight
43% of adults aged 18+ were overweight in 2022, and 890 million of them had obesity.
Source: WHO 2024
×2
Adult obesity has doubled
Worldwide adult obesity more than doubled between 1990 and 2022.
Source: WHO 2024
×4
Adolescent obesity has quadrupled
Obesity among adolescents aged 5–19 quadrupled from 1990 to 2022.
Source: WHO 2024
Related articles
More in Body & Weight
Questions people ask
Does intermittent fasting work for weight loss?
It can, mainly because it reduces total calories. Research shows weight loss similar to standard calorie-reduced diets.
Can I drink coffee while fasting?
Yes — black coffee, plain tea and water have virtually no calories. Milk, sugar and syrups break the fast.
Is 16:8 fasting safe?
For most healthy adults it is generally safe. It is not suitable for some groups, including pregnant women and people on diabetes medication, without medical advice.
Sources
- • NHS: Intermittent fasting overview
- • de Cabo & Mattson, NEJM (2019)
- • Lowe et al., JAMA Internal Medicine (2020)
- • BDA: Intermittent fasting
General information based on UK public health sources, not medical advice. Speak to your GP or a registered dietitian before major diet changes, especially if you are pregnant, have a health condition or take medication.