Effect of Time-Restricted Eating versus Daily Calorie Restriction on Mood and Quality of Life in Adults with Obesity

This study is a secondary analysis of a previously published 12-month randomized controlled trial [28]. The study compared the effects of 8 h TRE to those of daily CR on body weight and metabolic disease risk factors in adults with obesity. The Office for the Protection of Research Participants at the University of Illinois, Chicago, approved the experimental protocol, and all volunteers gave written informed consent to participate in the trial. Participants were recruited from the Chicago area through posters placed around the University of Illinois Chicago campus.

Inclusion criteria: male or female; age between 18 and 65 years; and BMI between 30 and 50 kg/m². Exclusion criteria: history of diabetes mellitus; history of eating disorders; use of medications that induce weight loss; weight unstable for 3 months prior to the beginning of the study (>4 kg weight loss or gain); eating within less than a 10 h window; perimenopausal; nightshift workers; pregnant or trying to become pregnant; and current smokers. Subjects were screened via BMI assessment, pregnancy test, questionnaire, and a food log. Subjects were randomized using a stratified random sampling protocol (by age, sex, and BMI) into one of three groups: 8 h TRE, 25% CR, or a no-intervention control group. The 12-month trial was divided into a 6-month weight loss phase followed by a 6-month weight maintenance phase. Due to the nature of the interventions, subjects could not be blinded as to their intervention assignment.

During the 6-month weight loss phase, TRE subjects were asked to eat only between the hours of 12:00 and 8:00 p.m. and to fast from 8:00 to 12:00 p.m. the following day. Subjects did not have to monitor food or energy intake during the 8 h eating window. During the 16 h fasting window, subjects were allowed to drink water and calorie-free beverages like coffee and tea without additives, and diet sodas (limit 2 per day). During the 6-month weight maintenance period, subjects were asked to maintain their weight by expanding their eating window to 10:00 a.m. to 8:00 p.m. (10 h eating window) and fast from 8:00 p.m. to 10:00 a.m. (14 h fasting window). TRE subjects received diet counseling (over Zoom) weekly during the first 3 months and then biweekly from months 4 to 12. During the counseling sessions, subjects learned how to make healthy food choices [29] and were also taught cognitive behavioral strategies to assist with controlling weight.

During the 6-month weight loss phase, CR subjects were asked to reduce their energy intake by 25% each day. Total energy expenditure was calculated using the Mifflin equation [30] and multiplied by the applicable activity factor for each participant. CR subjects met with the dietitian at the commencement of the study to develop weight loss meal plans according to their food preferences. During the 6-month weight maintenance phase, CR subjects were instructed to consume 100% of their newly calculated energy needs. CR subjects received diet counseling (over Zoom) weekly during the first 3 months and then biweekly from months 4 to 12. During the counseling sessions, subjects learned how to make healthy food choices [29] and were also taught cognitive behavioral strategies to assist with weight control.

Control subjects were asked to maintain their weight by not changing their eating and activity habits during the 12-month trial. Controls did not receive diet counseling but were contacted by the study coordinators at the same frequency as the TRE and CR groups to provide body weight measurements.

All variables were measured at baseline and month 12. Body weight was assessed without shoes, in light clothing, using a digital scale at the research center. Body composition (fat mass, lean mass, and visceral fat ass) was measured using dual X-ray absorptiometry (iDXA, GE). Waist circumference was measured using a measuring tape midway between the lowest rib and the iliac crest by trained study personnel.

Adherence to the TRE diet was measured using a paper or digital adherence log, which recorded the time each participant started and stopped eating each day. The day was labeled as adherent if the log showed that the subject ate within the correct eating window that day. If they did not, the day was labeled as nonadherent. Compliance with the TRE diet was expressed as percentage of adherent days from baseline to month 12. Adherence to CR was expressed as the percentage of participants who were compliant with their calorie targets (within ±200 kcal). Energy intake and dietary composition were assessed through a 7-day food log using the Automated Self-Administered 24-hour (ASA-24) diet assessment tool [31]. All subjects were instructed not to change their exercise habits during the trial. Physical activity (steps/d) was measured using a pedometer (Fitbit Alta HR) worn continuously for 7 days at baseline and month 12.

Mood was quantified with the Beck Depression Inventory II (BDI-II) [32] and the Profile of Mood States (POMS) [33]. The BDI-II is a reliable and valid measure of mood disturbance, with a score range of 0 to 63, where higher scores indicate worse mood [32]. More specifically, scores of 0–13 are considered no depression, 14–19 is mild depression, 20–28 is moderate depression, and 29–63 is severe depression [32]. The POMS has 6 subscales: tension (score range, 0–36), depression (score range, 0–60), anger (score range, 0–48), fatigue (score range, 0–28), vigor (score range, 0–32), and confusion (score range, 0–28), and a total mood disturbance (score range, −32 to 200) [33]. High vigor scores reflect a good mood or emotion, and low scores in the other subscales reflect a good mood or emotion. The total mood disturbance score is computed by adding the five negative subscale scores (tension, depression, anger, vigor, fatigue, and confusion) and subtracting the vigor score. Higher scores for the total mood disturbance score indicate a greater degree of mood disturbance.

Quality of life was measured using the Rand 36-Item Short Form (SF-36) [34]. The SF-36 has 4 subscales: 2 that measure mental aspects of quality of life (vitality and mental health) and 2 that measure physical aspects of quality of life (bodily pain and physical health). Scores on the SF-36 range from 0 to 100, with higher scores reflecting better quality of life.

Data are shown as mean (95% CI) unless otherwise noted. We conducted an intention-to-treat analysis, which included data from all 90 participants who were randomly assigned. Results are reported for the intention-to-treat analysis unless indicated otherwise. A linear mixed model was used to assess time, group, and time × group effects for each outcome. In each model, time and group effects (and their interaction) were estimated without imposing a linear time trend. For each outcome variable, linear modeling assumptions were assessed with residual diagnostics. To account for the potential for nonuniform variances (heteroskedasticity) between treatment groups due to random chance, all CIs and p values from linear mixed models were calculated using robust variance estimators (sandwich estimators). Pearson correlations were performed to assess the relationships between changes in body weight, physical activity, mood, and quality of life. All analyses were performed using R software.

As reported previously [28], 126 subjects were screened and 90 were randomized into the TRE group (n = 30), CR group (n = 30), or control group (n = 30). By the end of the 12-month study, the number of dropouts were as follows: TRE group n = 4 subjects, CR group n = 5 subjects, and control group n = 4 subjects. Reasons for dropping out were scheduling conflicts, personal reasons, and inability to contact. All baseline characteristics had similar distributions between the TRE, CR, and control groups (Table 1). The subjects were primarily non-Hispanic Black and Hispanic women with obesity.

Changes in body weight and body composition are reported in Table 2. By month 12, body weight significantly decreased in the TRE group (−4.87% [95% CI: −7.61, −2.13]) and CR group (−5.30% [95% CI: −9.06, −1.54]) versus controls, with no difference between the TRE and CR (0.43% [95% CI: −3.48, 4.34]). Fat mass was reduced in the TRE group (−2.77 kg [95% CI: −5.10, −0.43]) versus controls, but not in the CR group versus controls (−3.18 kg [95% CI: −6.85, 0.49]). Lean mass decreased in the CR group versus controls (−1.13 kg [95% CI: −2.24, −0.01]), but not in the TRE group versus controls (−0.81 kg [95% CI: −1.81, 0.20]). Visceral fat mass did not differ in the TRE and CR groups versus controls by month 12. Waist circumference was reduced in TRE group compared to the control group (−4.98 cm [95% CI: −8.09, −1.87]), but not in the CR group versus controls (−2.30 cm [95% CI: −6.55, 1.94]).

TRE subjects adhered to their eating window on 87% of days on average over the 12-month trial. In the CR group, 61% of subjects adhered to their prescribed calorie targets over 12 months. Energy intake decreased by −425 kcal/d (SD 531 kcal/d) in the TRE group and −405 kcal/d (SD 712 kcal/d) in the CR group, with no difference between groups, over 12 months. As reported previously [28], percent energy intake from protein, carbohydrates, and fat did not change over the course other trial in the TRE and CR groups versus controls. Changes in physical activity (steps per day) did not differ over time or between groups [28].

Changes in mood are presented in Table 2 and Figure 1. Results of the BDI-II survey show that the TRE group had mild depression at baseline, while the CR group and control group had no identifiable depression at baseline. The BDI-II depression score did not change in the TRE or CR group, versus controls, by month 12. The POMS tension, depression, anger, fatigue, and confusion scales were low at baseline, while the vigor (good mood) scale was high at baseline in all groups. Moreover, the POMS total mood disturbance score was low in all groups at baseline. Taken together, this would indicate that the participants in each group had a good general mood at the beginning of the study. By month 12, there were no changes in any of the POMS subscales or the total mood disturbance score in the TRE or CR groups versus controls.

Changes in quality of life are presented in Table 2 and Figure 2. At baseline, the SF-36 constructs of vitality, mental health, bodily pain, and general physical health were all moderately high in the TRE, CR, and control groups. This would indicate overall good quality of life in all groups at the beginning of the study. After 12 months of intervention, there were no significant changes in mental health, bodily pain, and general physical health in the TRE or CR groups versus controls. However, there was a trend towards increased vitality in the TRE group (7.77 [95% CI: 0.15, 15.39] p = 0.05), relative to controls.

There were no associations between changes in body weight, physical activity, mood, or quality of life in any group by the end of the study.