What counts as intermittent fasting?
The label covers several different approaches: daily time-restricted eating, alternate-day fasting and periodic plans such as 5:2. These approaches change when food is eaten and may also reduce how often someone has the opportunity to eat. They do not guarantee a calorie deficit.
Time-restricted eating
Meals fit inside a consistent daily window, such as ten hours. It is the easiest form for many people to test.
Alternate-day fasting
Very-low-intake days alternate with usual-intake days. It is more restrictive and not automatically easier to sustain.
5:2 or periodic fasting
One or two low-intake days are placed into the week. Weekly energy intake still determines whether weight falls.
Ordinary calorie restriction
Food timing stays flexible while portions or food choices create the deficit. This remains an equally valid option.
What the strongest recent reviews found
A 2026 Cochrane review found 22 studies involving 1,995 adults with overweight or obesity. In the comparison with regular dietary advice, 21 studies involving 1,430 people showed little to no difference in weight loss. The authors rated much of the evidence low or very low certainty and noted that the studies mainly covered periods of up to 12 months.
A 2025 BMJ network meta-analysis included 99 randomized trials and 6,582 adults. Intermittent-fasting strategies and continuous energy restriction both reduced body weight compared with unrestricted eating. Alternate-day fasting had a small average advantage over continuous restriction of about 1.3 kg, but the difference was modest and was not evidence that every fasting plan is superior.
“No better” does not mean “does not work”
- Fasting is one possible structure for eating fewer calories over time.
- Average trial results do not decide which routine will feel easiest for one person.
- A small statistical difference may not be large enough to matter in everyday life.
- Long-term adherence and safety data are less certain than short-term weight data.
Who may find it useful?
- You naturally prefer fewer, larger meals.
- A defined kitchen closing time reduces unplanned evening eating.
- You can still reach an appropriate protein, fiber and micronutrient intake.
- The schedule does not damage training performance, sleep or social life.
When it is a poor fit
A fasting schedule is not worth forcing if it produces rebound eating, persistent fatigue, worse training or obsessive food rules. People who are pregnant or breastfeeding, have a current or previous eating disorder, are under 18, or use glucose-lowering medication should not start a restrictive fasting plan without appropriate clinical guidance.
A practical two-week test
- Use a moderate window.Start with roughly 10–12 hours rather than an extreme schedule.
- Keep protein anchored.Plan substantial protein across the meals that remain.
- Track the whole week.Do not judge the plan by one fast or one weigh-in.
- Compare function.Check hunger, training, sleep and social friction—not only scale weight.
- Keep it only if it helps.The schedule is a tool, not a requirement for fat loss.
Research used in this guide
- Cochrane (2026): review of intermittent fasting versus regular dietary advice or no intervention.
- The BMJ (2025): network meta-analysis of 99 randomized clinical trials.