You may have heard of the “12-hour fast.” A few years back, researchers at the Salk Institute used animal models to premise that if we confined our eating to a 12 hour period daily, and followed that by 12 hours of fasting, we would be skinnier and healthy. It's now become a trues and true cornerstone of many modern diets, with various beneficial metabolic changes occurring during the fasting period.

Now, researchers at the University of Alabama have upped the ante, in both fasting hours and species. Conducting the first ever human testing of “early time-restricted feeding” (eTRF), the scientists have determined that people who eat their last meal by the mid-afternoon and do not eat again until breakfast the next morning reduced swings in hunger and altered fat and carbohydrate burning patterns. 

“Eating only during a much smaller window of time than people are typically used to may help with weight loss,” said Courtney Peterson, PhD, an associate professor in the Department of Nutrition Sciences at UAB. “We found that eating between 8 a.m. and 2 p.m. followed by an 18-hour daily fast kept appetite levels more even throughout the day, in comparison to eating between 8 a.m. and 8 p.m., which is what the average American does.”

Many of the aspects of metabolism that aid in digestion and glucose processing are at their optimal functioning in the morning. The scientists determined that eating in sync with our circadian rhythms is beneficial to our health. They tested the impact of eTRF on calories burned, fat burned and appetite. The results showed that, although eTRF did not affect how many total calories participants burned, it reduced their daily hunger swings and increased fat burning during several hours at night. Their metabolic flexibility –  their ability to switch between burning carbs and burning fats – was also heightened.

Peterson and her team tracked 11 men and women with excess weight over the course of 8 days of eating between 8 a.m. and 2 p.m., and four days of eating between 8 a.m. and 8 p.m. Test subjects tried both eating schedules, ate the same number of calories both times and completed all testing under supervision.

Still up in the air is whether eTRF has any long-term weight loss or other benefits. The researchers acknowledge that a larger and more comprehensive study will be necessary before making that call. They presented their results at The Obesity Society Annual Meeting at Obesity Week 2016 in New Orleans.