We all know that eating later in the day isn't good for our waistlines, but why? A new study weighed in on that question by comparing people who ate the same foods—but at different times in the day.
"We found that eating four hours later makes a significant difference for our hunger levels, the way we burn calories after we eat, and the way we store fat," Vujović said, a researcher at Boston's Brigham and Women's Hospital. "Together, these changes may explain why late eating is associated with increased obesity risk reported by other studies and provide new biological insight into the underlying mechanisms." The study provides support for the concept that circadian(生理节奏) rhythm, which influences key physiologic functions such as body temperature and heart rate, affects how our bodies absorb fuel, researchers said.
The study does show eating later results in "an increase in hunger, impacts hormones(荷尔蒙) and also changes gene expression, especially in terms of fat metabolism with a tendency towards less fat breakdown and more fat deposition," said Dr. Bhanu Prakash Kolla, a professor of psychiatry and psychology at the Mayo Clinic College of Medicine and a consultant to Mayo's Center for Sleep Medicine and Division of Addiction Medicine.
The study was small—only 16 overweight or obese people—but carefully planned to eliminate other potential causes of weight gain, the authors said. "While there have been other studies investigating why late eating associates with an increased risk for obesity, this may be the most well controlled, including strictly controlling the amount, composition and timing of meals, physical activity, sleep, room temperature and light exposure," said senior author Frank Scheer, director of the Medical Chronobiology Program in the Brigham's Division of Sleep and Circadian Disorders. All participants were in good health, with no history of diabetes or shift work, which can affect circadian rhythm, and had regular physical activity. Each person in the study kept to a strict healthy sleep/wake schedule for about three weeks and were provided with prepared meals at fixed times for three days before the lab experiment began.
Results showed that hunger pangs doubled for those on a night-eating regime. People who ate later in the day also reported a desire for starchy and salty foods, meat and, to a lesser extent, a desire for dairy foods and vegetables. By looking at the results of blood tests, researchers were able to see why: Levels of leptin, a hormone which tells us when we feel full, were decreased for late eaters versus early eaters. In comparison, levels of the hormone ghrelin, which spikes our appetite, rose.
