The first-line therapy prescribed to obese patients for weight loss is daily calorie restriction.¹ However, many patients find it difficult to adhere to a conventional weight-loss diet because food intake must be limited every day.² As such, adherence to daily calorie restriction decreases after 1 month and continues to decline thereafter.^3-5 In light of this limitation, another approach that requires individuals to restrict calories only every other day was developed.⁶ This strategy is called alternate-day fasting and involves a fast day where individuals consume 25% of their usual intake (approximately 500 kcal), alternated with a “feast day” where individuals are permitted to consume food ad libitum. Findings from short-term studies indicate that participants lose 3% to 7% of body weight after 2 to 3 months of alternate-day fasting and experience improvements in lipid profiles, blood pressure, and insulin sensitivity.^7-13

BACKGROUND: Time restricted feeding decreases energy intake without calorie counting and may be a viable option for weight loss. However, the effect of this diet on body weight in obese subjects has never been examined. OBJECTIVE: This study investigated the effects of 8-h time restricted feeding on body weight and metabolic disease risk factors in obese adults. DESIGN: Obese subjects ( n = 23) participated in an 8-h time restricted feeding intervention (ad libitum feeding between 10:00 to 18:00 h, water fasting between 18:00 to 10:00 h) for 12 weeks. Weight loss and other outcomes were compared to a matched historical control group ( n = 23). RESULTS: Body weight and energy intake decreased in the time restricted group (–2.6% ± 0.5; –341 ± 53 kcal/d) relative to controls over 12 weeks ( P < 0.05). Systolic blood pressure decreased in the time restricted feeding group (–7 ± 2 mm Hg) versus controls ( P < 0.05). Fat mass, lean mass, visceral fat mass, diastolic blood pressure, LDL cholesterol, HDL cholesterol, triglycerides, fasting glucose, fasting insulin, HOMA-IR, and homocysteine were not significantly different from controls after 12 weeks (no group×time interaction). CONCLUSION: These findings suggest that 8-h time restricted feeding produces mild caloric restriction and weight loss, without calorie counting. It may also offer clinical benefits by reducing blood pressure.

Time-restricted eating (TRE), without calorie counting, has become a popular weight loss strategy, yet long-term randomized trials evaluating its efficacy are limited. To determine whether TRE is more effective for weight control and cardiometabolic risk reduction compared with calorie restriction (CR) or control. 12-month randomized controlled trial. (ClinicalTrials.gov: NCT04692532). University of Illinois Chicago from January 2021 to September 2022. 90 adults with obesity. 8-hour TRE (eating between noon and 8:00 p.m. only, without calorie counting), CR (25% energy restriction daily), or control (eating over a period of 10 or more hours per day). Participants were not blinded. Change in body weight, metabolic markers, and energy intake by month 12. Seventy-seven persons completed the study. Mean age was 40 years (SD, 11), 33% were Black, and 46% were Hispanic. Mean reduction in energy intake was -425 kcal/d (SD, 531) for TRE and -405 kcal/d (SD, 712) for CR. Compared with the control group, weight loss by month 12 was -4.61 kg (95% CI, -7.37 to -1.85 kg; P ≤ 0.01) (-4.87% [CI, -7.61% to -2.13%]) for the TRE group and -5.42 kg (CI, -9.13 to -1.71 kg; P ≤ 0.01) (-5.30% [CI, -9.06% to -1.54%]) for the CR group, with no statistically significant difference between TRE and CR (0.81 kg [CI, -3.07 to 4.69 kg; P = 0.68]) (0.43% [CI, -3.48% to 4.34%]). Not blinded, not powered to detect relatively large differences in weight loss, and lack of adjustment for multiple comparisons. Time-restricted eating is more effective in producing weight loss when compared with control but not more effective than CR in a racially diverse population. National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases.

Time restricted feeding is a form of intermittent fasting where participants shorten the daily window in which they eat. This is the first study to examine the effects of intermittent fasting on changes in the gut microbiome. Adults with obesity (n = 14) participated in a daily 8-hour time restricted feeding intervention (8-hour feeding window/16-hour fasting window) for 12 weeks. Fecal microbiota were determined by 16 S rRNA (ribosomal ribonucleic acid) gene sequencing of stool samples. Body weight decreased (P < 0.05) by -2 ± 1 kg. Gut microbiota phylogenetic diversity remained unchanged. The two most common phyla were Firmicutes and Bacteroidetes accounting for 61.2% and 26.9% of total abundance at baseline. No significant alterations in the abundance of Firmicutes, Bacteroidetes, or any other phyla were detected after 12 weeks of time restricted feeding. Time restricted feeding did not significantly alter the diversity or overall composition of the gut microbiome.