Time Restricted Feeding (4-hour Versus 6-hour) for Weight Loss in Obese Adults

The aims of this proposal are to compare the effects of 4-h versus 6-h time restricted feeding (TRF) on body weight and metabolic disease risk factors in adults with obesity. To test the study objectives, a 10-week randomized, controlled, parallel-arm trial, divided into 2 consecutive periods: (1) 2-week baseline period; and (2) 8-week TRF weight loss period, will be implemented. Obese subjects will be randomized to 1 of 3 groups: (1) 4-h TRF, (2) 6-h TRF, or a no-intervention control group. This study will be the first randomized controlled trial to compare 4-h versus 6-h TRF.

Modest weight loss of 5-10% is sufficient to reduce metabolic disease risk in obese individuals. The first line of therapy prescribed for weight loss is daily calorie restriction (CR; 25% restriction every day). However, adherence to CR greatly diminishes after 4-6 weeks, due to subject frustration with constantly having to count calories and never being able to eat freely. In light of these issues with CR, another approach that limits timing of food intake, instead of number of calories consumed, has been developed. This strategy is termed time restricted feeding (TRF), and involves confining the period of food intake to 8 h/d (10 am to 6 pm) without calorie counting. Preliminary findings of 8-h TRF demonstrate modest weight loss and blood pressure reductions after 12 weeks. What remains unknown however, is whether shorter feeding windows during TRF (such as 4-h or 6-h feeding windows) can produce even greater weight loss in obese adults. Also of interest, is the impact of these shorter feeding windows on metabolic disease risk indicators (such as plasma lipids, blood pressure, and insulin resistance, inflammation and oxidative stress). Accordingly, the aims of this proposal are: AIM 1: To compare the effects of 4-h versus 6-h time restricted feeding (TRF) on body weight in adults with obesity; AIM 2: To compare the effects of 4-h versus 6-h TRF on metabolic disease risk factors in adults with obesity. To test the study objectives, a 10-week randomized, controlled, parallel-arm trial, divided into 2 consecutive periods: (1) 2-week baseline period; and (2) 8-week TRF weight loss period, will be implemented. Obese subjects will be randomized to 1 of 3 groups: (1) 4-h TRF, (2) 6-h TRF, or a no-intervention control group. This study will be the first randomized controlled trial to compare 4-h versus 6-h TRF on body weight and metabolic disease risk markers.

4-h TRF subjects will consume food ad libitum between 3pm and 7pm (4-h feeding window), and refrain from eating and drinking caloric beverages from 7pm to 3pm (20-h fasting window) each day. These subjects will not be instructed to limit/monitor energy intake during the feeding window. Subjects will be encouraged to drink plenty of water during the fasting period.

Controls will be instructed to maintain their weight throughout the trial, and not to change eating or physical activity habits. Controls will visit the research center at the same frequency as the TRF groups (for outcome measurements).

6-h TRF subjects will consume food ad libitum between 1pm and 7pm (6-h feeding window), and refrain from eating and drinking caloric beverages from 7pm to 1pm (18-h fasting window) each day. These subjects will not be instructed to limit/monitor energy intake during the feeding window. Subjects will be encouraged to drink plenty of water during the fasting period.

TRF subjects will consume food ad libitum during the feeding window (4-h or 6-h window), and refrain from eating during the fasting window (20-h or 18-h window)

Change from baseline to week 8 in sex steroid levels (estrogen, androgens, sex hormone binding globulin)

Inclusion Criteria: Male or female; body mass index (BMI) between 30.0 and 49.9 kg/m2; age between 18 and 65 years; sedentary (light exercise less than 1 h per week) or moderately active (moderate exercise 1 to 2 h per week); weight stable for >3 months prior to the beginning of the study (gain or loss <4 kg); able to give written informed consent Exclusion Criteria: Smoker; diabetic; taking weight loss medications; taking medication that requires eating food before (or with) the medication; history of eating disorders; night-shift workers; perimenopausal; pregnant women

Cienfuegos S, Gabel K, Kalam F, Ezpeleta M, Lin S, Varady KA. Changes in body weight and metabolic risk during time restricted feeding in premenopausal versus postmenopausal women. Exp Gerontol. 2021 Oct 15;154:111545. doi: 10.1016/j.exger.2021.111545. Epub 2021 Aug 31.

Cienfuegos S, Gabel K, Kalam F, Ezpeleta M, Wiseman E, Pavlou V, Lin S, Oliveira ML, Varady KA. Effects of 4- and 6-h Time-Restricted Feeding on Weight and Cardiometabolic Health: A Randomized Controlled Trial in Adults with Obesity. Cell Metab. 2020 Sep 1;32(3):366-378.e3. doi: 10.1016/j.cmet.2020.06.018. Epub 2020 Jul 15.