A groundbreaking clinical trial from the University of Illinois at Chicago (UIC) demonstrates that two time-restricted eating approaches—4-hour and 6-hour daily fasting windows—are effective for weight loss. Led by nutrition expert Krista Varady, PhD, the study compared these regimens against a control group over 10 weeks.
"This is the first human clinical trial to compare the effects of two popular forms of time-restricted diets on body weight and cardiometabolic risk factors," said Varady, professor of nutrition at UIC's College of Applied Health Sciences and the study's corresponding author.
Participants in the 4-hour group ate only between 1:00 PM and 5:00 PM, while the 6-hour group ate between 1:00 PM and 7:00 PM. They could eat freely within their windows—no calorie counting required—and consumed only water or calorie-free beverages during fasting periods. The control group maintained their usual habits.
Both fasting groups naturally cut about 550 calories daily, shedding roughly 3% of body weight. They also showed reductions in insulin resistance and oxidative stress compared to controls. No changes were observed in blood pressure, LDL/HDL cholesterol, or triglycerides, and results were similar between the 4-hour and 6-hour groups.
"These findings reinforce that time-restricted eating is a practical weight loss strategy, especially for those avoiding calorie tracking or restrictive diets," Varady noted. "No added benefits from the stricter 4-hour window suggest 6 hours may suit most people—pending further research on optimal durations."
Importantly, no serious side effects occurred; mild issues like dizziness or headaches were rare and short-lived, mainly at the study's start.
