Time-Restricted Eating May Improve Metabolic Syndrome

Adults with metabolic syndrome and elevated blood sugar levels who eat within a time-restricted window may experience modest improvements in several measures, including A1c levels, weight, and body fat, according to a randomized controlled trial published in Annals of Internal Medicine.

For the study, participants kept to an 8- to 10-hour window of eating, a dietary practice called time-restricted eating or intermittent fasting.

“We’re hopeful the findings of this study can help others who are looking to address their metabolic syndrome and reduce the risk for type 2 diabetes,” said Pam R. Taub, MD, a cardiologist at UC San Diego Health System.

Taub said time-restricted eating offers an accessible, cost-effective, and sustainable intervention for the average patient. 

Metabolic syndrome can result in patients developing a wider waistline and elevated glucose, high blood pressure, and high cholesterol levels. The condition affects approximately one third of Americans, or about 112 million people. 

Time-restricted eating and fasting leads to a “metabolic switch” that helps the body burn fat and ketones, said Mark P. Mattson, PhD, adjunct professor in the Department of Neuroscience at Johns Hopkins University School of Medicine in Baltimore. “The ketones have significant effects on the neuroendocrine system, like reducing appetite.”

To determine the efficacy of time-restricted eating, Taub and her colleagues examined data from 54 participants who completed the 12-week intervention. Adults were eligible if they had metabolic syndrome plus an elevated A1c (between 5.7% and 7.0%) or fasting glucose (between 5.56 and 6.95 mmol/L), in line with prediabetes. Management medications were allowed. 

The standard-of-care group (n = 54) received nutritional counseling from a registered dietician. Participants in the intermittent group also received this intervention but were additionally instructed to eat within the 8- to 10-hour timeframe and to stop intake of food 3 hours before bedtime. 

Baseline levels of glycemic regulation were comparable between groups. Medication use was also similar, with 6% of participants taking metformin for prediabetes, 48% for hyperlipidemia, and 69% taking at least one drug for cardiometabolic health. Participants overall had a body mass index (BMI) of 31.22 and a mean age of 56 years, and a little over half were women. 

The primary outcomes were A1c and glycemic parameters, such as fasting glucose, fasting insulin, and homeostatic model assessment for insulin resistance (HOMA-IR). Secondary outcomes included lipid profile, C-reactive protein (CRP), and trunk fat. 

From baseline to 3 months, the time-restricted-eating group experienced reductions in A1c by 0.12% while the standard-of-care group saw a 0.02 reduction, a -1.7 relative reduction (between-group difference [BGD], -0.10%; 95% CI, -0.19% to -0.003%). 

Fasting glucose, fasting insulin, and HOMA-IR all showed greater reductions for the time-restricted-eating group than the standard-of-care group but were not statistically significant. 

The time-restricted-eating group also showed greater decreases than the standard-of-care group in weight (BGD, -1.66; 95% CI, -3.00 to -0.32) and BMI (BGD, -0.77; 95% CI, -1.37 to -0.17). Body fat and trunk fat also decreased more in the time-restricted-eating group.

The researchers observed no significant changes between groups in total lean mass or total bone mineral content, which Taub said indicates that intermittent fasting is a safe intervention for decreasing weight and A1c levels.

“This [study] is consistent with other studies that have shown a benefit to intermittent fasting, or time-restricted eating,” said Mir Ali, MD, a bariatric surgeon and medical director of the MemorialCare Surgical Weight Loss Center in Fountain Valley, California. 

Ali said the most common form of intermittent fasting is an 8-hour window, which research has shown may help patients lower glucose metabolism. 

“For most people, it is easiest to do part of this period at night as you will be sleeping for a good part of the time period,” he said. “Of course, choosing the right foods is the most important thing for weight loss.” 

Mattson said he wonders whether reducing the eating window could lead to greater health improvements. For example, other studies have indicated greater success with a shorter eating window. 

“They found very clear, more pronounced effects on insulin sensitivity and body fat than the present study,” Mattson said. 

Naysha Isom, MD, a family medicine physician and founder of Isom MD, a primary care clinic in Las Vegas, said instructing patients to end eating 3 hours prior to bed is especially relevant to clinical practice. 

“With additional proof showing avoiding late-night eating helps blood sugar control and fat reduction, doctors may give their patients unambiguous, evidence-based nutritional recommendations,” she said, noting that physicians should include nutrition recommendations in their core curriculum with patients. 

With obesity and insulin resistance on the rise in the United States, Isom said evidence-based advice about time-restricted eating can be easily incorporated into routine visits or added to an after-visit summary. 

“Even brief advice on avoiding late-night meals can have a significant impact on patient health without requiring physicians to become nutrition experts,” she said. 

Study authors reported no relevant financial disclosures. The research was funded by grants from the National Institutes of Health, the Translational Research Institute, the Salk Institute Cancer Center, and the Robert Wood Johnson Foundation, among others. 

Lisa M. Basile, MFA, is an award-nominated health writer and author.