Researchers at UAB have discovered that meal timing strategies -- like intermittent fasting or eating earlier in the daytime -- appear to help people lose weight. This approach was also shown to lower appetite rather than burn more calories, according to a report published online today in the journal Obesity.
The study is the first to show how meal timing affects 24-hour energy metabolism when food intake and meal frequency are matched.
"We suspect that a majority of people may find meal timing strategies helpful for losing weight or to maintain their weight since these strategies naturally appear to curb appetite," said Courtney Peterson, PhD, one of the study's authors and an assistant professor in the Department of Nutrition Sciences.
Peterson and her colleagues also reported that meal timing strategies may help people burn more fat on average during a 24-hour period. Early Time-Restricting Feeding (eTRF) -- a form of daily intermittent fasting where dinner is eaten in the afternoon -- helped to improve people's ability to switch between burning carbohydrates for energy to burning fat for energy, an aspect of metabolism known as metabolic flexibility. The study's authors say, however, that the results on fat-burning are preliminary.
For the study, researchers enrolled 11 adult men and women who had excess weight. Adults, in general good health, age 20 to 45 years old were eligible to participate if they had a body mass index between 25 and 35 kg/m2 (inclusive), body weight between 68 and 100 kg, a regular bedtime between 9:30 p.m. and 12 a.m., and for women, a regular menstrual cycle.
Participants tried two different meal timing strategies in random order: a control schedule where participants ate three meals during a 12-hour period with breakfast at 8 a.m. and dinner at 8 p.m. and an eTRF schedule where participants ate three meals over a six-hour period with breakfast at 8 a.m. and dinner at 2 p.m. The same amounts and types of foods were consumed on both schedules. Fasting periods for the control schedule included 12 hours per day, while the eTRF schedule involved fasting for 18 hours per day.
Study participants followed the different schedules for four days in a row. On the fourth day, researchers measured the metabolism of participants by placing them in a respiratory chamber where researchers measured how many calories, carbohydrates, fat and protein were burned. Researchers also measured the appetite levels of participants every three hours while they were awake, as well as hunger hormones in the morning and evening.
Although eTRF did not significantly affect how many calories participants burned, the researchers found that eTRF did lower levels of the hunger hormone ghrelin and improved some aspects of appetite. It also increased fat-burning over the 24-hour day.
"By testing eTRF, we were able to kill two birds with one stone," said Peterson, adding that the researchers were able to gain some insight into daily intermittent fasting (time restricted-feeding), as well as meal timing strategies that involve eating earlier in the daytime to be in sync with circadian rhythms.
The researchers believe that these two broader classes of meal timing strategies may have similar benefits to eTRF. Peterson says prior research has been conflicted on whether meal timing strategies help with weight loss by helping people burn more calories or by lowering appetite. The study's authors say, however, that previous studies did not directly measure how many calories people burned or were imperfect in other ways.