Loath as you may be to admit it, chances are that at some point you have found yourself in the kitchen late at night, devouring some sweet, salty or carb-rich treat even though you weren't hungry.
Scientists are getting closer to understanding why people indulge after dark and to determining whether those nighttime calories wreak more havoc -- whether they drive up the risk of weight gain and of chronic diseases such diabetes -- than ones consumed earlier in the day.
"For years, we said a calorie is a calorie no matter when you consume it," says dietitian Joy Dubost, a spokeswoman for the Academy of Nutrition and Dietetics. "I don't know if we can say that anymore, based on the emerging research. The timing of a meal may potentially have an impact."
Most of the major studies on late-night eating have been conducted with animals, night-shift workers and people who, due to a disorder called night eating syndrome, consume at least 25 percent of their daily calories after supper or who wake up to eat at least twice a week.
Studies tend to show that when food is consumed late at night -- anywhere from after dinner to outside a person's typical sleep/wake cycle -- the body is more likely to store those calories as fat and gain weight rather than burn it as energy, says Kelly Allison of the University of Pennsylvania School of Medicine's Center for Weight and Eating Disorders.
Some animal studies have shown that food is processed differently at different times of day. This could be due to fluctuations in body temperature, biochemical reactions, hormone levels, physical activity, and absorption and digestion of food, says Steven Shea, director of the Oregon Institute of Occupational Health Sciences at Oregon Health & Science University.
"The studies suggest that eating out of our normal rhythm, like late at night, may prompt weight gain" and higher levels of blood sugar, which can raise the risk of chronic disease, Allison says.
Not enough research on what prompts weight gain has been done, Allison says, to determine whether timing is as important as -- or even more important than -- the types or amounts of food often consumed at night. People tend to choose more highly palatable items -- sweet and salty foods, which tend to be more caloric -- when they're tired and have restrained themselves all day, Allison adds. And night-shift workers tend to overestimate how many calories they need to stay awake while on duty.
Two recent studies have shed new light on the potential impact of timing. In a 2013 study of 420 overweight or obese people, those who ate their major meal after 3 p.m. lost less weight during a 20-week weight-loss program than those who ate that main meal before 3 p.m. -- even when the amount they ate, slept and exercised was the same.
"This is the first study to show that eating later in the day . . . makes people lose less weight, and lose it slower," says the study's lead author, Marta Garaulet, a professor of physiology at the University of Murcia in Spain. "It shows that eating late impairs the success of weight-loss therapy." In the 2013 study, the early eaters lost 22 pounds, the late eaters only 17.
In a subsequent small study of healthy women published this year, Garaulet and her team showed that when participants ate lunch after 4:30 p.m., they burned fewer calories while resting and digesting their food than they did when they ate at 1 p.m. -- even though the calories consumed and level of activity was the same.
What's more, when the participants ate late, they couldn't metabolize, or burn off, carbohydrates as well as when they ate earlier. They also had decreased glucose tolerance, which can lead to diabetes.
STAY ON TRACK AT NIGHT
To stop your diet from getting derailed at night:
Don't restrict what you eat so severely during the day, says Traci Mann, a professor of psychology at the University of Minnesota and author of "Secrets From the Eating Lab: The Science of Weight Loss, the Myth of Willpower and Why You Should Never Diet Again." That way, you won't have to control yourself as much at night, and you won't be preoccupied with feeling hungry and rebound with food you've been forbidding yourself to eat.
Keep junk food out of the house. Don't buy tempting indulgences: If they're not in your cupboard, refrigerator or freezer, you can't surrender to them when you go foraging at 10 p.m. "If it's not there, you can't eat it," Mann says.
Eat early. Eat your main meal earlier in the day if you can: Lunchtime is better than dinnertime, Shea says. And stop all eating about three hours before bedtime, Dubost says.
Keep after-dinner snacks small. Limit yourself to 100 to 200 calories, Dubost says.
Take good notes. Keeping a journal and tracking what, how much and why you eat can help you foster the awareness that will ultimately help you resist temptation, says Heather McKee, who teaches behavior change psychology at Britain's St. Mary's University, Twickenham. "If you track your lapses and understand your triggers, you're more likely to overcome them," she says.