There’s now been a number of well-controlled studies comparing IF to a more traditional approach to weight loss. All of them fail to find major differences between them, the latest, just published in JAMA, and below is the essential details, along with earlier studies. I’m not against IF per se, but those making claims there’s a metabolically unique effect from IF vs traditional approaches when calories are matched, ignore the the actual data. What IF does for some is simply leads them to consume less calories, and that’s it. No magic is taking place. But, some find following an IF schedule helps them achieve their goals of weight loss, and that’s what matters all things being equal.
If you find IF works for you and helps get the fat off, then no harm done and carry on, just don’t buy into the clearly debunked claims it’s anything but good old calorie reduction packed differently and my advice/conclusions below this latest study remain unchanged:
Calorie Restriction with or without Time-Restricted Eating in Weight Loss
N Engl J Med 2022; 386:1495-1504
List of authors.
The long-term efficacy and safety of time-restricted eating for weight loss are not clear.
We randomly assigned 139 patients with obesity to time-restricted eating (eating only between 8:00 a.m. and 4:00 p.m.) with calorie restriction or daily calorie restriction alone. For 12 months, all the participants were instructed to follow a calorie-restricted diet that consisted of 1500 to 1800 kcal per day for men and 1200 to 1500 kcal per day for women. The primary outcome was the difference between the two groups in the change from baseline in body weight; secondary outcomes included changes in waist circumference, body-mass index (BMI), amount of body fat, and measures of metabolic risk factors.
Of the total 139 participants who underwent randomization, 118 (84.9%) completed the 12-month follow-up visit. The mean weight loss from baseline at 12 months was −8.0 kg (95% confidence interval [CI], −9.6 to −6.4) in the time-restriction group and −6.3 kg (95% CI, −7.8 to −4.7) in the daily-calorie-restriction group. Changes in weight were not significantly different in the two groups at the 12-month assessment (net difference, −1.8 kg; 95% CI, −4.0 to 0.4; P=0.11). Results of analyses of waist circumferences, BMI, body fat, body lean mass, blood pressure, and metabolic risk factors were consistent with the results of the primary outcome. In addition, there were no substantial differences between the groups in the numbers of adverse events.
Among patients with obesity, a regimen of time-restricted eating was not more beneficial with regard to reduction in body weight, body fat, or metabolic risk factors than daily calorie restriction
Previous studies and Comments:
A study the prestigious JAMA did not find benefits of IF compared to the more traditional approach. (1)
Another recent study (2) following the popular 5:2 IF schedule vs a calorie matched restricted calorie diet, yet again, found no statistically significant differences in endpoints studied, which was weight weight cardiometabolic factors:
“Intermittent energy restriction was as successful in achieving modest weight loss over a 24-month period as continuous energy restriction.”
The study ran a full year and followed over 100 people. The Abstract is posted blow.
Intermittent Fasting (IF) continues to be a popular approach to weight loss. It’s not a new approach, and most of my comments HERE still hold up. Since that vid, a number of studies in humans have been done, and the effects have not been impressive. The study below, the largest to date, that ran 50 weeks, did not find major differences in weight loss, and other endpoints looked at.
I’m not ready to dismiss IF per se, as there’s still more questions then answers but controlled studies continue to fail to demonstrate benefits. In the second study, in obese non-exercising people, a 5;2 IF protocol was not superior to calorie matched diet for weight loss. The next step would be comparing different IF protocols. For example, perhaps the 5:2 approach may not potentiate endocrine adaptation as well as other approaches, or maybe different protocols will be more effective for different populations. Fact is, we don’t have the answers at this time, and what exists for human studies small and or short term.
Also, what impact does IF have on performance or strength? Does a strength or physique athlete respond differently to IF than say an endurance athlete? What about lean vs people with higher bodyfat levels? There’s still plenty of Qs to be answered regarding IF…
Bottom line at this time: find the approach you find most beneficial to your goals, but don’t fall for IF being a magical approach to fat loss, cuz it’s not. It’s still about the calories. Some recent thoughts on calories vs exercise worth a read HERE also as well as understanding the 3,500 calorie myth HERE.
(2) Effects of intermittent and continuous calorie restriction on body weight and metabolism over 50 wk: a randomized controlled trial
The American Journal of Clinical Nutrition, Volume 108, Issue 5, 1 November 2018, Pages 933–945,
Will Brink is the owner of the Brinkzone Blog. Will has over 30 years experience as a respected author, columnist and consultant, to the supplement, fitness, bodybuilding, and weight loss industry and has been extensively published. Will graduated from Harvard University with a concentration in the natural sciences, and is a consultant to major supplement, dairy, and pharmaceutical companies.
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