Calorie and Time Restriction in Weight Loss
Calorie Restriction with or without Time-Restricted Eating in Weight Loss.
Liu D, Huang Y, Huang C, et al;
N Engl J Med. 2022 Apr 21;386(16):1495-1504. [Full text]
Obesity is an epidemic and the health benefits of weight loss for those that are obese are clear and well established. Achieving significant or sustained weight loss, however, has been elusive. Any number of diets and interventions have been touted, but most when studied lead to modest (pounds in the single digits) that are not well long lived (return to baseline weight at ~1 year). Regardless, caloric restriction generally is a shared thread between dietary lifestyle changes.
Time-restricted eating is restricting intake of calories to a consistent time period of less than 10 hours without explicit attempts to modify diet composition or reduce calories. The physiologic explanation for a potential benefit are that, owing to the circadian rhythm, caloric handling not uniform through the day (more weight storage after evening meals) and/or that periods of fasting alter the handling of calories [1]. Observational studies have shown some benefit to this strategy. It can be argued that time restriction is inherently a form of caloric restriction. The current study is a randomized prospective trial aimed to compare caloric restriction alone to time-restricted eating in addition to caloric restriction to assess if there is an additional benefit to limiting the time period one eats.
Patient population and Design
Participants aged 18 to 75 years with a BMI of 28-45 were eligible. Exclusion criteria included acute or chronic viral hepatitis, malignant tumors, diabetes, serious liver dysfunction or chronic kidney disease, current smoking, serious cardiovascular or cerebrovascular disease within 6 months, severe gastrointestinal diseases or gastrointestinal surgery within 12 months, active participation in a weight-loss program, use of medications that affect weight or energy balance, and current or planned pregnancy.
For 12 months men in the trial were instructed to follow a 1500-1800 kcal/day diet while women were to follow a 1200-1500 kcal/day diet. Approximately 75% of calories were to be split as follows 40-55% from carbohydrates, 15-20% protein, and 20-30% fat. Participants also received one protein shake per day for the first 6 months to help improve adherence to the permitted calorie intake, and all the participants received dietary counseling for the duration of the trial. Time restriction was to be an 8-hour period from 8:00 a.m. to 4:00 p.m. Only noncaloric beverages were permitted outside of that 8-hour window.
Dietary counseling was conducted by trained health coaches. Participants received written dietary information booklets that provided portion advice and sample menus that included dietary caloric restrictions similar to those described in current dietary guidelines for macronutrient intake.12,13 Participants were encouraged to weigh foods to ensure they accurately reported their caloric intake. During the first 6 months of the trial, all the participants were required to write in a daily dietary log, photograph the food they ate, and note the time at which they ate with the use of a custom mobile study application (app).
Participants in the daily-calorie-restriction group were required to limit their food consumption to the prescribed daily calories; participants assigned to the time-restricted–eating group were required both to eat within the prescribed daily time period for eating and to meet the daily caloric-intake goal.
Outcomes
The primary outcome was the difference between in the change in body weight from baseline at 12 months. The secondary outcomes included changes in waist circumference (area measurements of the abdominal visceral fat and subcutaneous fat were obtained by CT at the 4th/5th lumbar vertebral level), body fat, body lean mass (quantified with the use of a whole-body dual radiography system), and metabolic risk factors, including levels of plasma glucose, insulin sensitivity, serum lipids, and blood pressure. The body fat mass and lean mass were quantified with the use of a whole-body dual radiography system (Lunar iDXA, GE Healthcare). Liver fat was measured via with transient elastography and insulin-resistance status was measured with the homeostasis model assessment of insulin resistance (HOMA–IR).
Results
From November 30, 2018, through July 28, 2021, 139 patients were randomly assigned to either time-restricted eating (69 participants) or daily calorie restriction (70 participants). Of the total number who underwent randomization, 135 participants (97.1%) completed the 6-month intervention and 118 (84.9%) completed the 12-month intervention. The mean weight was 88.2±11.6 kg and physical activity was similar in the two groups over the 12 months of the trial. Both groups had an average eating window of 10 hr and 20+ min before the intervention (which prescribed an 8 hour window).
During the 12-month intervention, the mean days participants adhered to both the prescribed calories and eating period was 84.0±16.1% in the time-restricted–eating group and 83.8±12.6% in the daily-calorie-restriction group.
The mean weight change from baseline to 12 months was −8.0 kg (95% CI, −9.6 to −6.4) in the time-restricted–eating group and −6.3 kg (95% CI, −7.8 to −4.7) in the daily-calorie-restriction group, a difference that was not significant (net △−1.8 kg; 95% CI, −4.0 to 0.4; P=0.11). In addition, participants in the two groups had similar reductions from baseline in waist circumference (net △−1.8 cm; 95% CI, −4.0 to 0.5) and BMI (net △−0.7; 95% CI, −1.5 to 0.1; P=0.11).
Discussion
Over the 12-month trial period, an 8-hour time-restricted–eating regimen did not produce more weight loss than the regimen of daily calorie restriction alone, Waist circumference, body-mass index, body fat, and blood pressure also all improved, but without a significant differences between the groups.
The study was well designed to maximize adherence to the assigned regimens with diaries requiring photos of all food ingested, dietary supplements, twice per week reminders and health coach meetings every 2 weeks. One could argue, however, that all this adherence coaching does not represent real world conditions. Time-restricted–eating may be easier to adhere to without such help.
Proponents for time restricted eating could also point to this population’s baseline eating window of just over 10 hours perhaps being atypical. As the prescribed restriction window was only 8 hours, the change may not have been that significant. Further studies would be needed in order to confirm this and otherwise support time restricted eating. For the time being it seems that there remains no proven substitute to calorie restriction for weight loss.
| F: Follow up | Yes |
| R: Randomization | Yes |
| I: Intention to treat | Yes |
| S: Similar at baseline | Yes |
| B: Blinding | Yes |
| E: Equal treatment | Yes |
| S: Source (funding) | National Key Research and Development Project and others |
- Laferrère B, Panda S. Calorie and Time Restriction in Weight Loss. N Engl J Med. 2022 Apr 21;386(16):1572-1573.
