Mealtime clocking versus calorie counting for weight loss

Obesity affects one-half of US adults and is a costly public health issue [(1)]. Lifestyle intervention with a focus on caloric restriction (CR) remains the first and main recommendation for weight loss, but it is tedious, imposes a burden on patients who do not always have the resources to implement it, and is rarely sustainable in the long term. Meal timing has recently been shown to be a key factor to consider in dietary interventions, in addition to calorie amount and diet composition. Late eating, having prolonged eating windows, and erratic eating patterns are associated with obesity and metabolic disorder [(2-4)]. Time restricted eating (TRE), i.e., limiting the number of hours during which one can eat during the day, may present a useful and less-cumbersome alternative to CR to achieve weight loss in humans [(2, 5)]. In the study by Oldenburg et al. [(6)], 88 participants with obesity with a mean age of 43.2 years and a baseline eating window duration of ~14 h were randomized to a 12-week intervention: either an 8-h TRE, a 15% CR, or unrestricted eating (UE). A battery of tests was performed at baseline and at the end of the study to assess total body fat by dual x-ray absorptiometry, subcutaneous and visceral adipose tissue by abdominal magnetic resonance, insulin sensitivity and metabolic flexibility by a two-step clamp and indirect calorimetry, sleep and physical activity by actigraphy, and glucose by continuous glucose monitoring. Calorie intake was assessed by diet recalls. Additionally, meal timing was recorded in real time during the 2-week baseline and at the end of intervention. The TRE and UE groups were required to time-stamp their meals with the myCircadianClock phone application, whereas the CR group could use MyFitnessPal to monitor calories. The eating window duration was established using data from the phone application and diet recalls, whereas energy and nutrient intake was assessed by dietary recalls. The 24 authors [(6)], including senior author Lisa Chow, should be complimented on this trial, which used comprehensive metabolic and body composition measurements and had an excellent retention rate of 92%. The TRE intervention shortened the duration of the eating window by ~4 h to a 10-h window, which was 2 h short of the study target, with a resulting mean weight loss of 3 kg (95% confidence interval [CI]: −4.9 to 1.3). The CR and UE groups did not change their eating window and lost 4.1 and 1.6 kg, respectively, with no difference in weight loss between groups. There was no change in energy expenditure in either group, and the TRE group did not improve body composition, glycemia (measured via clamp, hemoglobin A1c), or metabolic flexibility when compared with the CR or UE groups. Although the CR restriction intervention aimed at a 15% reduction of daily calories, the effective reduction was only 9%, which could explain the absence of weight-loss differences with TRE. Nevertheless, the data on energy intake and diet quality should be interpreted with caution, as diet was measured with diet recalls only, which are notoriously inaccurate [(7)]. CR resulted in greater metabolic flexibility but more hunger than TRE. In the TRE and UE groups, a decrease of the eating window by 1 h, or 10%, which had no effect on weight loss, was associated with a decrease in visceral adipose tissue. The results of this well-conducted randomized trial with state-of-the art measures of metabolism and body composition show that applying a self-selected restricted 10-h eating window resulted in modest weight loss and could be a reasonable alternative to CR [(6)]. However, the weight loss resulting from TRE had no significant effect on metabolism in a cohort of individuals with obesity but without metabolic syndrome, bringing into question the efficacy of a 3-month TRE intervention. The self-selected window, although possibly increasing adherence, may not have necessarily aligned with each participant chronotype, which may have muddied the results. Although there was a good sex distribution, participants were young and predominantly White, and generalizability of the results to wider age groups and different ethnicity needs to be determined. More research is needed to elucidate the impact of the optimal duration of the eating window; whether clinical obesity, rather than simple obesity [(8)], needs to be the target population; and whether a longer TRE intervention, perhaps coupled with an earlier caloric distribution or other lifestyle modification, may have a greater efficacy on body composition and metabolism. Blandine Laferrère disclosed a financial relationship with UpToDate and membership in The Obesity Society Governing Board. Leinys S. Santos-Báez receives financial support from the Russell Berrie Foundation Fellow Award and the Leadership Education and Advancement Program (LEAP) for Early Career Scholars from the American Psychological Association.