Dear Doctors: I recently read about a study that says eating late makes it easier to gain weight. I would like to know more about that. I've been having success with weight loss by not eating after 6 p.m., and I wonder if the timing has anything to do with that.
Dear Reader: Although eating late at night has long been linked to an increased risk of obesity, the reasons why have not been clear. Possible theories included an increase in total calorie consumption, the poor food choices that can occur later in the day and night, and the surge in blood sugar that would accompany those choices.
Now, the results of a small study conducted by researchers at a medical center in Massachusetts add some specifics. The researchers found that when study participants ate later in the day and at night, it increased hunger, lowered metabolism and caused physiological changes to fat tissues.
The study looked at 16 adults who ranged from overweight to obese. They prepared for the study by syncing their sleep and wake times for two to three weeks. Three days before the start of the study, they ate the same meals at the same time of day.
For the study itself, each person followed an early meal schedule for two weeks, followed by two weeks of consuming all of their calories four hours later in the day and into the night. The participants were provided with identical meals, which were eaten at the same time. They also followed the same sleep-wake cycle and maintained the same level of physical activity.
The researchers took frequent daily blood samples and performed regular fat biopsies and tests to measure total energy expenditure. Participants also closely documented their levels of appetite and hunger throughout the day and night.
Lab tests found that when eating extended into the night, it had a measurable effect on levels of leptin and ghrelin. These are hormones that play an important role in appetite regulation. Levels of leptin, which signals the body that you have had enough to eat, dropped and remained suppressed. Meanwhile, levels of ghrelin, also known as the hunger hormone, became elevated. Not surprisingly, this led to increased levels of hunger during the late-night eating part of the study.
At the same time, metabolic tests showed that when meals skewed later, the participants burned calories at a slower rate. Researchers also saw changes to fat tissue that are associated with preserving and adding to fat reserves.
Taken together, the results suggest that eating later in the day and into the night may trigger metabolic changes that encourage weight gain. The researchers believe this is influenced by the body's circadian cycle, which is tied to the 24-hour cycle of light and dark.
When it comes to your own weight loss, it is possible that the 6 p.m. cutoff time you have adopted is helping with appetite control. But it is important to remember that when it comes to weight loss and weight maintenance, a healthful and balanced diet, regular exercise and getting enough sleep also play a role.
(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)
