Weight
Does intermittent fasting actually work? What randomised trials found
Quick answer
Intermittent fasting can help some people lose weight, but mainly because it helps them eat less, not because of the timing itself. In a 12-month randomised trial, people who ate within an 8-hour window and cut calories lost 8.0 kg, against 6.3 kg for people who cut calories alone. The difference was not statistically significant.
Skip breakfast, eat between noon and 8pm, and the weight falls off. That is the promise of 16:8. For busy professionals who already skip breakfast, it sounds perfect. So what happens when it is tested properly?
What the trials found
| Trial | Who took part | What they compared | Result |
|---|---|---|---|
| Lowe et al. (JAMA Internal Medicine, 2020) | 116 adults with overweight or obesity, 12 weeks | Eating within 8 hours a day vs three regular meals | 0.94 kg vs 0.68 kg lost, no significant difference |
| Liu et al. (NEJM, 2022) | 139 adults with obesity, 12 months | Calorie cut plus eating 8am–4pm vs the same calorie cut at any time | 8.0 kg vs 6.3 kg lost, no significant difference |
In both trials, the clock on its own made little difference. In the second trial, both groups lost meaningful weight because both groups ate fewer calories.
What most people miss
Fasting is a tool, not a magic window. If a shorter eating window helps you stop late-night snacking and eat less overall, it can be useful. If it leaves you starving at 7pm and grazing until midnight, it will not help. The trials also remind us that early windows (finishing by 4pm) are hard to keep with client dinners and late meetings.
The bigger wins for weight are still the dull ones: total food intake, protein and fibre, regular activity and enough sleep.
Should you try it?
- It may suit you if: you are not hungry in the morning, you snack late at night, and a clear rule makes eating simpler.
- It may not suit you if: you take diabetes medication, have a history of disordered eating, are pregnant, or find it makes you overeat later. Speak to a doctor first.
- If you try it: keep your meals balanced with protein and vegetables, and judge it after eight weeks by how you feel and what you eat, not only the scale.
FAQs
Is 16:8 better than calorie counting? Trials so far show similar weight loss. Choose the approach you can keep up.
Does fasting speed up metabolism? The trials above did not show a meaningful metabolic advantage over simply eating less.
Is skipping breakfast bad for me? Not necessarily. What matters more is your total intake and the quality of your meals.
For the years that matter, Dr Lwin
This article is general education, not personal medical advice. If you have symptoms or concerns, speak to your GP.