Intermittent fasting: does it work better than a regular diet?
Nutrition
Key points
- NEJM trial (12 months): calorie restriction with and without a time window led to similar weight loss.
- A 16:8 trial found weight loss was not significantly different from control.
- The effect comes mainly from eating fewer calories.
- Choose the approach you can stick with.
What the research shows
One-year trial. In a randomized trial of 139 adults with obesity, both groups followed a calorie-restricted diet, and one group also ate only between 8 a.m. and 4 p.m. After 12 months, weight loss was similar: about 8 kg (18 lb) with the time window and 6.3 kg (14 lb) without, a difference that was not statistically significant. Blood pressure, blood sugar and cholesterol changed similarly too (Liu et al., 2022).
The TREAT trial. In a 12-week randomized trial of 116 adults, eating only between noon and 8 p.m. without other guidance led to very modest weight loss that did not differ significantly from the control group, which ate three meals a day (Lowe et al., 2020).
Breakfast. A meta-analysis of randomized trials found that eating breakfast did not help with weight loss, and skipping it did not cause weight gain (Sievert et al., 2019).
Bottom line
Intermittent fasting is not magic. It works when it helps you eat less overall, and it is roughly as effective as ordinary calorie reduction. If an eating window helps you stop late-night snacking, it may be a good tool. If it leads to overeating at the end of the day or feels like a struggle, choose another approach.
Frequently asked questions
Does 16:8 speed up metabolism?
There is no good evidence that it does. Weight loss with time-restricted eating comes mainly from eating less overall.
Is skipping breakfast harmful?
A meta-analysis found that skipping breakfast does not cause weight gain; what matters is the total amount and quality of food.
Sources
- Liu et al. (2022). Calorie Restriction with or without Time-Restricted Eating in Weight Loss. New England Journal of Medicine 386(16):1495-1504. doi:10.1056/NEJMoa2114833
- Lowe et al. (2020). Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity. JAMA Internal Medicine 180(11):1491. doi:10.1001/jamainternmed.2020.4153
- Sievert et al. (2019). Effect of breakfast on weight and energy intake: systematic review and meta-analysis of randomised controlled trials. BMJ :l42. doi:10.1136/bmj.l42
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