2020 Update:

A study just out in 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.

(1) Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity

JAMA Intern Med. Published online September 28, 2020.
Key Points
Question 
 
What is the effect of time-restricted eating on weight loss and metabolic health in patients with overweight and obesity?
 
Findings  In this prospective randomized clinical trial that included 116 adults with overweight or obesity, time-restricted eating was associated with a modest decrease (1.17%) in weight that was not significantly different from the decrease in the control group (0.75%).
 
Meaning  Time-restricted eating did not confer weight loss or cardiometabolic benefits in this study.

 
Abstract
 
Importance  The efficacy and safety of time-restricted eating have not been explored in large randomized clinical trials.
 
Objective  To determine the effect of 16:8-hour time-restricted eating on weight loss and metabolic risk markers.
 
Interventions  Participants were randomized such that the consistent meal timing (CMT) group was instructed to eat 3 structured meals per day, and the time-restricted eating (TRE) group was instructed to eat ad libitum from 12:00 pm until 8:00 pm and completely abstain from caloric intake from 8:00 pm until 12:00 pm the following day.
 
Design, Setting, and Participants  This 12-week randomized clinical trial including men and women aged 18 to 64 years with a body mass index (BMI, calculated as weight in kilograms divided by height in meters squared) of 27 to 43 was conducted on a custom mobile study application. Participants received a Bluetooth scale. Participants lived anywhere in the United States, with a subset of 50 participants living near San Francisco, California, who underwent in-person testing.
 
Main Outcomes and Measures  The primary outcome was weight loss. Secondary outcomes from the in-person cohort included changes in weight, fat mass, lean mass, fasting insulin, fasting glucose, hemoglobin A1c levels, estimated energy intake, total energy expenditure, and resting energy expenditure.
 
Results  Overall, 116 participants (mean [SD] age, 46.5 [10.5] years; 70 [60.3%] men) were included in the study. There was a significant decrease in weight in the TRE (−0.94 kg; 95% CI, −1.68 to −0.20; P = .01), but no significant change in the CMT group (−0.68 kg; 95% CI, -1.41 to 0.05, P = .07) or between groups (−0.26 kg; 95% CI, −1.30 to 0.78; P = .63). In the in-person cohort (n = 25 TRE, n = 25 CMT), there was a significant within-group decrease in weight in the TRE group (−1.70 kg; 95% CI, −2.56 to −0.83; P < .001). There was also a significant difference in appendicular lean mass index between groups (−0.16 kg/m2; 95% CI, −0.27 to −0.05; P = .005). There were no significant changes in any of the other secondary outcomes within or between groups. There were no differences in estimated energy intake between groups.
 
Conclusions and Relevance  Time-restricted eating, in the absence of other interventions, is not more effective in weight loss than eating throughout the day.

(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,

ABSTRACT
 
Background
 
Although preliminary evidence suggests that intermittent calorie restriction (ICR) exerts stronger effects on metabolic parameters, which may link obesity and major chronic diseases, compared with continuous calorie restriction (CCR), there is a lack of well-powered intervention studies.
 
Objective
 
We conducted a randomized controlled trial to test whether ICR, operationalized as the “5:2 diet,” has stronger effects on adipose tissue gene expression, anthropometric and body composition measures, and circulating metabolic biomarkers than CCR and a control regimen.
 
Design
 
One hundred and fifty overweight and obese nonsmokers [body mass index (kg/m2) ≥25 to <40, 50% women], aged 35–65 y, were randomly assigned to an ICR group (5 d without energy restriction and 2 d with 75% energy deficit, net weekly energy deficit ∼20%), a CCR group (daily energy deficit ∼20%), or a control group (no advice to restrict energy) and participated in a 12-wk intervention phase, a 12-wk maintenance phase, and a 26-wk follow-up phase.
 
Results
 
Loge relative weight change over the intervention phase was −7.1% ± 0.7% (mean ± SEM) with ICR, −5.2% ± 0.6% with CCR, and −3.3% ± 0.6% with the control regimen (Poverall < 0.001, PICR vs. CCR = 0.053). Despite slightly greater weight loss with ICR than with CCR, there were no significant differences between the groups in the expression of 82 preselected genes in adipose tissue implicated in pathways linking obesity to chronic diseases. At the final follow-up assessment (week 50), weight loss was −5.2% ± 1.2% with ICR, −4.9% ± 1.1% with CCR, and −1.7% ± 0.8% with the control regimen (Poverall = 0.01, PICR vs. CCR = 0.89). These effects were paralleled by proportional changes in visceral and subcutaneous adipose tissue volumes. There were no significant differences between ICR and CCR regarding various circulating metabolic biomarkers.
 
Conclusion
 
Our results on the effects of the “5:2 diet” indicate that ICR may be equivalent but not superior to CCR for weight reduction and prevention of metabolic diseases.
 
Impact of intermittent vs. continuous energy restriction on weight and cardiometabolic factors: a 12-month follow-up. Int J Obes (2020)
 
Abstract

 
Background and objectiveIntermittent energy restriction continues to gain popularity as a weight loss strategy; however, data assessing it’s long-term viability is limited. The objective of this study was to follow up with participants 12 months after they had completed a 12-month dietary intervention trial involving continuous energy restriction and two forms of intermittent energy restriction; a week-on-week-off energy restriction and a 5:2 programme, assessing long-term changes on weight, body composition, blood lipids and glucose.
 
Subjects and methods 109 overweight and obese adults, aged 18–72 years, attended a 12-month follow-up after completing a 12-month dietary intervention involving three groups: continuous energy restriction (1000 kcal/day for women and 1200 kcal/day for men), week-on-week-off energy restriction (alternating between the same energy restriction as the continuous group for one week and one week of habitual diet), or 5:2 (500 kcal/day on modified fast days each week for women and 600 kcal/day for men). The primary outcome was weight change at 24 months from baseline, with secondary outcomes of change in body composition, blood lipids and glucose.
 
Results For the 109 individuals who completed the 12-month follow-up (82 female, 15 male, mean BMI 33 kg/m2), weight decreased over time with no differences between week-on and week-off and continuous energy restriction or 5:2 and continuous energy restriction with −4.5 ± 4.9 kg for continuous energy restriction, −2.8 ± 6.5 kg for week-on, week-off and −3.5 ± 5.1 kg for 5:2. Total cholesterol reduced over time and glucose, HDL, LDL and triglycerides were unchanged.
 
Discussion and conclusion Intermittent energy restriction was as successful in achieving modest weight loss over a 24-month period as continuous energy restriction.
6 Comments
  1. elizabeth maron 2 years ago

    Will, are there any studies on other health benefits from IF that are not regarding weight loss? Cholesterol, insulin resistance, autophagy, as those are the band wagon claims for reasons to IF too.

    • Author
      Will Brink 2 years ago

      In this study, they looked at “various circulating metabolic biomarkers” and found no differences. The specifics can be found in the full paper linked. There are small studies that didn’t last long that have suggested improvements in various metabolic biomarkers other than weight loss were improved with IF, but larger studies being done coming out have been – as is often the case – much less impressive in those endpoints.

  2. Ross 2 months ago

    Ive heard Layne Norton suggest 95% of health improvement is directly causal by weight loss. Is that an overstatement of current evidence?

    • Author
      Will Brink 1 month ago

      No sure that number is based on specific data but it’s no doubt accurate within a margin of that figure. You’d have to ask him for a source.

  3. Keith Wallin 3 weeks ago

    As a personal trainer and a Level One Precision Nutrition coach, I have found both methods work also. Some people find it easier to restrict calories and others find it easier to fast. I would be interested to see a study done with a 19;5 protocol. Brad Pilot in his book “Eat, Stop, Eat”, claims that the optimum benefit of fasting is 19 hours. The 16:8 is easier to follow and is the most popular. Thanks for the current update, Will.

  4. Christian Dehlinger 3 weeks ago

    Interesting. What I have found at 60, I stay leaner. The pad around my navel is reduced and my side fat is almost non-existent. I have not tested but signs such as regular nighttime erections and desire, I think my test is higher. I lead an active work life; spools of cable, up and down ladders and stairs. Pushing not eating past the 18hr mark, everyday, and with minimal resistance training, I am lean. Training has been abbreviated as my business demands are great at this time (Internet & AV systems;can’t get my work done) still moves forward. I cycle just a few exercises for one set, mostly of ETUT; (Extended Time Under Tension). This is performed by utilizing all the tricks, reducing distance of the weight to the joint, breath catches during the set and forced reps through cheats. I still believe the Zercher squat is one of the overall greatest exercises and that super-setting DB bi’s and tri’s without stopping; is a super upper body foundational movement. Be well all.

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