Time-restricted eating (TRE) is an increasingly popular dietary intervention for weight management. TRE involves restricting the eating window to a shorter period each day, allowing for a longer fasting period. This approach is hypothesized to reinforce the metabolic benefits of nightly fasting, such as a shift from glucose to ketone utilization, reducing inflammation and oxidative stress. While studies have shown that TRE can improve various cardiometabolic health markers, most are small and haven't examined the combination of TRE with a comprehensive weight loss program. This study investigated the effects of a 14-hour daily fasting period (14:10 TRE) combined with a commercial weight loss program (Jenny Craig® Rapid Results™), comparing it to a 12-hour daily fast (12:12 TRE) as an active comparator. A key aspect was the inclusion of a low-calorie, high-fat, low-carbohydrate, low-protein 'fasting snack' in the 14:10 group at hour 12 to potentially improve adherence and maintain ketosis. The study aimed to determine the impact on body weight and fasting blood glucose (FBG) in participants with obesity, specifically exploring whether the fasting snack affected blood glucose levels.

Existing literature on TRE suggests various benefits, including improved visceral and total fat mass, glucose tolerance, insulin sensitivity, lipid profiles, blood pressure, appetite regulation, inflammatory markers, and gut microbiome composition. However, most human clinical trials investigating TRE's impact on weight loss are small pilot studies with mixed results. While many show weight loss with TRE, some do not. Notably, there is a lack of research combining TRE with a comprehensive commercial weight-loss program, which typically incorporates controlled diets, exercise plans, and personalized coaching.

This 8-week, randomized, controlled, virtual clinical trial included 78 men and women (BMI ≥ 30 kg/m²) recruited through the Jenny Craig® Rapid Results™ program between June and October 2020. Participants were randomized 1:1 to either a 14:10 TRE intervention or a 12:12 TRE active control group. The 14:10 group began a 14-hour fast after dinner and ended with breakfast 14 hours later. A 200-kcal fasting snack (high-fat, low-carb, low-protein) was consumed at hour 12 on five days a week. The 12:12 group followed a 12-hour fast, with no fasting snack. Both groups followed the Jenny Craig® Rapid Results™ program, which included controlled-calorie meals, exercise advice, and weekly coaching. Study procedures were conducted remotely using telemedicine due to COVID-19 restrictions. Weekly body weight and bi-weekly fasting blood glucose (FBG) were measured. Data analysis included least squares (LS) means comparisons and repeated measures analysis for body weight and FBG, considering gender as a covariate. The primary outcome was change from baseline in body weight in the 14:10 group; secondary outcomes included FBG changes in both groups, and changes in FBG in a subset with elevated baseline FBG (≥100 mg/dl).

Of the 78 participants, 60 completed the 8 weeks. In the completer population, the 14:10 TRE group exhibited a significantly greater mean reduction in body weight (-10.7 kg, -8.5%) compared to the 12:12 group (-8.9 kg, -7.1%). This difference (-1.9 kg, -1.4%) was statistically significant (P<0.05). Furthermore, the 14:10 group showed a statistically significant reduction in FBG (-7.6 mg/dl, P<0.05), whereas the 12:12 group showed a non-significant reduction (-3.1 mg/dl). Repeated measures analyses showed significant reductions in body weight and FBG in both groups across all time points. In the subset of participants with elevated baseline FBG (≥100 mg/dl), both groups showed significant FBG reductions, but the 14:10 group exhibited a numerically larger decrease. The fasting snack in the 14:10 group did not impact 14-hour blood glucose levels and was reported to improve satiety and adherence. Intent-to-treat analysis showed significant weight loss in both groups but no significant difference between them.

This study demonstrated that combining TRE with a structured commercial weight loss program resulted in significant and clinically meaningful weight loss and FBG improvements within 8 weeks. The 14:10 TRE schedule produced greater weight loss and FBG reduction compared to the 12:12 schedule, particularly benefiting individuals with higher baseline FBG. The lack of significant difference between groups in the ITT analysis might be attributed to missing data. The positive impact on FBG aligns with research suggesting TRE improves glucose tolerance and insulin sensitivity, especially in those at higher metabolic risk. The study highlights the importance of a comprehensive weight loss approach incorporating diet control, exercise, and behavioral support. The virtual study design, while necessary, may have introduced limitations due to reliance on self-reported data and the remote nature of participant support.

This virtual clinical trial provides evidence that combining TRE with a comprehensive weight loss program leads to significant weight loss and improvements in FBG. The 14:10 TRE schedule, potentially facilitated by the fasting snack, showed superior effects. Larger, longer-term studies are needed to confirm these findings and investigate the long-term effects and durability of the intervention.

The study's limitations include its relatively small sample size, the short 8-week duration, and the reliance on self-reported data and remote monitoring. The virtual setting prevented the collection of certain data points such as blood pressure, lipids, and body composition analysis. Attrition due to scheduling conflicts related to changing COVID-19 restrictions is another limitation. Finally, the small numerical difference in baseline body weight between groups could have influenced the results.