By Ellen Feldman, MD
Synopsis: In a randomized trial, adding time-restricted eating (limiting eating to an eight- to 10-hour window) to standard nutritional counseling improved hemoglobin A1c, glycemic control, and other markers of cardiometabolic health when compared to standard treatment alone.
Source: Manoogian ENC, Wilkinson MJ, O’Neal M, et al. Time-restricted eating in adults with metabolic syndrome: A randomized controlled trial. Ann Intern Med 2024;177:1462-1470.
With obesity and prediabetes on the rise, primary care faces an urgent challenge: how to mitigate the increasing risks of heart disease, type 2 diabetes, and other serious complications tied to these chronic conditions. Practical, sustainable lifestyle interventions that easily integrate into patients’ routines are essential for effective prevention.1,2
Time-restricted eating (TRE) is a one such strategy, involving the restriction of food intake to a set window each day — typically eight to 10 hours — and sometimes as short as six hours or fewer. This lifestyle intervention does not necessarily require caloric reduction, but instead capitalizes on aligning eating patterns with the body’s circadian rhythms. This alignment may enhance metabolism and reduce cardiometabolic risk factors over time.3,4
Noting that previous studies on TRE’s cardiovascular benefits have shown mixed results, Manoogian et al conducted a study to assess the effect of a personalized eight- to 10-hour TRE regimen combined with standard of care (SOC) over three months, comparing it to SOC alone. The goal: to determine whether adding TRE could meaningfully impact cardiometabolic health measures, potentially offering a valuable tool for addressing these growing health risks.
The study enrolled 122 adult volunteers, all with elevated body mass indexes (BMIs) and metabolic syndrome indicators, such as elevation in fasting glucose or hemoglobin A1c (HbA1c). Participants were randomly assigned into one of two arms of this study — the TRE or SOC/control group. All preexisting medications, including metformin and statins, were continued throughout the study. Both groups received standard nutritional and dietary counseling, and participants were not advised to specifically reduce caloric intake. Dietary intake was entered by participants and recorded electronically via a specialized app (myCircadianClock), which also provided messaging and guidance on topics such as restful sleep, stress reduction, and physical activity.5 Continuous glucose monitors were worn by participants to track glycemic levels.
In the TRE group, participants were assigned an eight- to 10-hour eating window personalized on the basis of baseline eating patterns. This was determined by calculating at least a four-hour reduction in the eating window from baseline, with eating ending at least three hours from participants’ usual bedtimes. Only water and medication were permitted outside the eating window. By the end of the study, the TRE group’s average eating window started at 9:14 a.m. and ended at 6:59 p.m., representing an average reduction of nearly five hours from baseline and an average of 4.30 hours fewer than the eating window of the SOC group.
Participants were monitored over three months, with follow-ups conducted both electronically and in-person. Results indicated that the TRE group achieved a modest but statistically significant improvement in HbA1c levels compared to the control arm (SOC), with a reduction of -0.10% (95% confidence interval [CI], -0.19% to 0.003%). Although seemingly modest, even slight reductions in HbA1c are clinically meaningful in lowering the risk of developing type 2 diabetes.6
Additionally, the TRE group showed reductions in fasting glucose, insulin, and markers of glycemic variability compared to SOC, suggesting improved glycemic stability. This enhanced stability could translate to better long-term cardiometabolic health outcomes.6,7
Participants in the TRE arm also experienced greater reductions in body weight, BMI, and body fat (particularly trunk fat) compared to participants in the SOC arm, without a decrease in lean mass.
Secondary outcomes, such as improvements in low-density lipoproteins and other cardiometabolic risk factors showed promising trends in the TRE group, although not all the changes were statistically significant.
Commentary
Imagine guiding patients to a health intervention that does not require counting calories, banning specific foods, or measuring portion sizes, yet still shows promise in boosting glycemic control and improving heart health. For many, this is the appeal of TRE. However, with inconsistent findings on the benefits of this intervention, it has been challenging to confidently advise patients on its use.3,4
Manoogian et al bring needed clarity to the field by introducing a personalized approach to TRE, tailoring the eating window based on participants’ baseline data. By focusing on patients with risk factors for metabolic syndrome and combining TRE with standard nutritional counseling, the study brings a realistic and applicable perspective to TRE research.
One strength of this study is the use of continuous glucose monitoring, allowing researchers to track both intra- and inter-daily fluctuations in glucose levels in all participants. The observed reduction in glucose variability among TRE participants is significant, since high glycemic variability is linked to an increased risk of diabetes-related complications, suggesting a potential benefit of TRE for long-term metabolic health.6,7
Another notable feature of this study was the use of the myCircadianClock app to facilitate personalized guidance and real-time monitoring. However, the study still relied on self-reported dietary data, which is an area for improvement in future studies.
An additional study limitation was the relatively short duration. While three months provides a useful initial assessment, a longer follow-up period could offer valuable insights into the trajectory of the findings over time and the sustainability of the observed benefits. Furthermore, while results were adjusted for age, variations in participant characteristics like body composition and socioeconomic factors could influence outcomes, warranting further research to confirm TRE’s effects across diverse populations.
Most importantly, the study did not specifically examine the mechanisms behind the observed improvements in metabolic parameters. It is possible that simply reducing the eating window indirectly reduced calorie intake, with the resulting weight loss playing a central role in the observed effects. Understanding these underlying mechanisms will be a critical focus for future research, since it could clarify whether TRE’s benefits stem from meal timing alone or primarily are driven by unintentional calorie reduction.
Even with its limitations, this trial offers an intriguing look at how TRE, combined with standard lifestyle counseling, can serve as an effective adjunct to traditional care. The findings open opportunities for the primary care clinician to discuss and help patients implement a practical lifestyle change that resonates with patients’ schedules and may be implemented without a massive dietary overhaul. For primary care professionals looking for sustainable, manageable approaches to address conditions like prediabetes and metabolic syndrome, TRE, in combination with nutritional advice, emerges as an adaptable and potentially powerful option.
Ellen Feldman, MD, works for Altru Health System, Grand Forks, ND.
References
- Healthy People 2030. Diabetes. U.S. Department of Health and Human Services. https://odphp.health.gov/healthypeople/objectives-and-data/browse-objectives/diabetes
- Centers for Disease Control and Prevention. Adult obesity facts. Updated May 14, 2024. https://www.cdc.gov/obesity/adult-obesity-facts/index.html#:~:text=Many%20U.S.%20adults%20have%20obesity,BMI%20of%2040.0%20or%20higher
- Moon S, Kang J, Kim SH, et al. Beneficial effects of time-restricted eating on metabolic diseases: A systemic review and meta-analysis. Nutrients 2020;12:1267.
- Chen JH, Lu LW, Ge Q, et al. Missing puzzle pieces of time-restricted-eating (TRE) as a long-term weight-loss strategy in overweight and obese people? A systematic review and meta-analysis of randomized controlled trials. Crit Rev Food Sci Nutr 2021;63:2331-2347.
- Dr. Satchin Panda’s Lab. myCircadianClock. Salk Institute. https://www.mycircadianclock.org
- Davies MJ, Aroda VR, Collins BS, et al. Management of hyperglycemia in type 2 diabetes, 2022. A consensus report by the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD). Diabetes Care 2022;45:2753-2786.
- American Diabetes Association Professional Practice Committee. 6. Glycemic targets: Standards of medical care in diabetes — 2022. Diabetes Care 2022;45(Suppl_1):S83-S96.
In a randomized trial, adding time-restricted eating (limiting eating to an eight- to 10-hour window) to standard nutritional counseling improved hemoglobin A1c, glycemic control, and other markers of cardiometabolic health when compared to standard treatment alone.
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