NEW YORK: Sugar, carbs, fat - it's hardly news that these are big contributors to unwanted weight. Now, add a fourth - lack of sleep.

Yes, according to a recent study carried out by researchers in the United States, people who get less sleep at night are more likely to choose food the next day that will put on extra pounds.

"It's possible people are less motivated to make healthy food choices when they're really tired," according to Tony Wells, a graduate student who co-wrote the study with Dr Dean Cruess, in the 'Psychology and Health' journal.

In fact, the researchers at the University of Pennsylvania came to the conclusion after recording the sleep hours and food intake of 50 undergraduates over a period of four days, and calculating the number of calories in meals.

In the first night, the participants slept for eight hours while in the second night they slept for four hours or less. On the following day, the researchers found that the sleepy students mainly chose foods based on convenience - whatever was easiest to prepare or buy.