Isocaloric Time-Restricted Eating May Not Induce Weight Loss in Patients with Obesity

Nisa Maruthur, MD, MHS

Credit: American Heart Association

Although past research has reported reduced body weight with time-restricted eating, findings from a recent randomized, isocaloric feeding study suggest restricted food timing may not have a notable impact on weight or glycemic outcomes relative to usual eating patterns.¹

The study was published in Annals of Internal Medicine and featured in a plenary session at the 2024 American College of Physicians (ACP) Internal Medicine meeting in Boston, where lead investigator Nisa Maruthur, MD, MHS, associate professor at Johns Hopkins Medicine, presented an overview of the research and its key findings.¹

According to the US Centers for Disease Control and Prevention (CDC), the US obesity prevalence was 41.9% in 2017 - March 2020.² The CDC cites healthy eating, physical activity, optimal sleep, and stress reduction as key considerations for achieving and maintaining a healthy weight.³ However, recently, many have pointed to the potential impact of the timing of eating.

“Misalignment of food timing with circadian rhythms contributes to adiposity and impaired glucose homeostasis in experimental models, raising the possibility that changing the timing of eating could be a viable intervention for obesity,” Maruthur and colleagues wrote.¹

To determine the effect of time-restricted eating versus a usual eating pattern on body weight in the setting of stable caloric intake, investigators conducted a randomized, isocaloric feeding study of adults with obesity and prediabetes or diet-controlled diabetes. For inclusion, patients were required to be 18 - 69 years of age; have hemoglobin A 1c (HbA1c) 5.7% - 6.4% or HbA1c 6.5% - 6.9% without use of any diabetes medications; body mass index (BMI) 30 - 50 kg/m2; stable medication regimen for hypertension, if present, for the past 6 months; and willingness to adjust timing of eating, consume study diet and nothing else, and complete study measurements.¹

After excluding individuals with clinically significant sleep or circadian rhythm disorders; persons routinely following a time-restricted eating window of 10 hours or less; persons with estimated glomerular filtration rate < 30 mL/min/1.73 m2; and persons with chronic health conditions or use of medications that might affect glucose levels, body weight, or adherence, investigators enrolled 41 eligible patients. Participants were randomly assigned in a 1:1 ratio to time-restricted eating or usual eating pattern for 12 weeks.¹

Those in the time-restricted group were instructed to consume all of their calories between 8 a.m. and 6 p.m., with 80% by 1 p.m, while participants in the usual eating group were instructed to consume all of their calories between 8 a.m. and midnight, with the majority after 5 p.m.¹

Of note, both groups had the same nutrient content and were isocaloric with total calories determined at baseline, and were instructed to consume breakfast, lunch, dinner, and a snack. Participants were provided specific instructions on the timing of these meals, which were prepared in the study metabolic kitchen supervised by research dietitians.¹

Data was collected at clinic visits scheduled at baseline and then at 4, 8, and 12 weeks after the start of the intervention. Investigators used standardized questionnaires to collect data on demographics, socioeconomic status, medical history, concomitant medications, and adverse event data. Participants recorded their adherence to recommended timing of eating and study diets in a diary.¹

The primary outcome was change in body weight at 12 weeks. Secondary outcomes included fasting glucose, homeostatic model assessment for insulin resistance (HOMA-IR), glucose area under the curve by oral glucose tolerance test, and glycated albumin.¹

Among the cohort, the mean age was 59 years, 93% of participants were female, 93% of participants were Black, and the mean BMI was 36 kg/m2. Baseline weight was 95.6 kg (210.8 lbs; 95% CI, 89.6 - 101.6 kg) in the time-restricted group and 103.7 kg (228.6 lbs; CI, 95.3 - 112.0 kg) in the usual eating group.¹

Participants ate all of their meals within 30 minutes of the recommended time window on 96.0% and 95.6% of study days in the time-restricted and usual eating groups, respectively. Adherence to the study diet occurred on 92.8% and 94.6% of study days in the time-restricted and usual eating groups, respectively.¹

In the time-restricted eating group, the mean difference in weight from baseline to 12 weeks was 2.3 kg (5 lbs; CI, 3.5 - 1.0 kg). In the usual eating practice group, the mean difference in weight from baseline to 12 weeks was 2.6 kg (5.7 lbs; CI, 3.7 - 1.5 kg), a 0.3 kg difference (0.66 lbs; CI, 1.2 - 1.9 kg) compared to the time-restricted group.¹

Investigators noted changes in glycemic measures also did not differ between groups, and there were no clinically relevant changes in blood pressure or lipids. Additionally, no treatment-related adverse events were reported in either group.¹

Investigators highlighted the single-site study design with a small sample size of primarily Black women, baseline differences in weight between groups, and reliance on daily diaries to measure adherence to time-restricted eating as key limitations to these findings.¹

Still, they concluded, “In the setting of isocaloric intake of a healthy diet among persons with obesity and impaired glucose homeostasis, 10-hour TRE combined with eating earlier in the day did not decrease weight or improve glucose homeostasis relative to a UEP of eating later in the day.”

References

1. ^{Maruthur NM, Pilla SJ, White K, et al. Effect of Isocaloric, Time-Restricted Eating on Body Weight in Adults With Obesity. Ann Intern Med. doi:10.7326/M23-3132}
2. ^{US Centers for Disease Control and Prevention. Adult Obesity Facts. Overweight & Obesity. May 17, 2022. Accessed April 21, 2024. https://www.cdc.gov/obesity/data/adult.html}
3. ^{US Centers for Disease Control and Prevention. Healthy Weight, Nutrition, and Physical Activity. June 9, 2023. Accessed April 21, 2024. https://www.cdc.gov/healthyweight/index.html}