Fourth meal is doing nobody no good. Not only is a healthy weight associated with a full night's sleep, but a recent study shows something more shocking and immediate—cutting down on sleep hours over just a week can lead to immediate weight increase.

Certainly stress, income, other lifestyle factors affect both sleep and nutrition. Researchers have long known that sleeping less than five hours a night is associated with weight gain for adults, and weight gain for children is associated with sleeping less than ten hours a night. But this study reveals that the weight and sleep association is not just about a lifestyle, it's an immediate relationship.

Sleep researchers at the University of Colorado studied 16 healthy men and women over two weeks and published their results in the Proceedings of the National Academy of Sciences. The researchers imposed strict sleep schedules on the participants and then painstakingly measured their metabolism and eating habits (every single bite they consumed). They wanted to see how sleep loss over just one week, something that would occur during exams or in the face of looming work deadlines, would affect people's weight and behavior.

For the first week, half the group could sleep a full nine hours and half the group was restricted to five. For the second week, the sleep schedules switched. All groups were given unlimited access to food.

Amazingly, staying up late increased metabolism. The sleep-deprived participants burned 111 more calories a day. However, this group more than made up for this calorie-burn increase by chomping away on a ton of food. The group that had reduced sleeping time ate 6% more food than the people who got nine hours—resulting in a weight gain that averaged two pounds. When the sleep schedule switched, the group that had lost sleep and gained the weight began to lose some of the weight they have put on in their first week of restricted sleep.

The researchers believe that the weight gain was mostly due to psychological factors. When people were sleep-deprived they couldn't resist carby, fatty food or late-night snacking. They consumed more calories while snacking after dinner than in other meal meal during the day. More sleep lead to more healthful eating (fewer carbs and fats). While a carefully calculated lab study of this phenomena is certainly a helpful step on the path to helping people learn more about managing their weight, the researchers could have visited any late-night area of a university library to meticulously observe some twizzler/pizza/soda gluttony.

[New York Times, image via Getty]