Why do females gain weight?

Girls and young women who devote much time to the internet, get too little sleep or regularly drink alcohol are more likely than their peers to put on excess weight, a new study suggests.The researchers, who followed more than 5,000 girls between 14 and 21 years old for one year, found that the more spare time girls spent on the internet, the more their body mass index (BMI) increased.

Similar patterns were seen when the researchers looked at alcohol consumption and sleep. In the latter case, lack of sleep was linked to greater gains in BMI -- a measure of weight in relation to height.The findings, reported in the Journal of Paediatrics , add to evidence implicating each of these three habits in promoting weight gain. The effect of each may be small, but over time the pounds can add up, according to the researchers, led by Catherine Berkey of Brigham & Women's Hospital and Harvard Medical School in Boston.

The study involved 5,036 girls and young women who were surveyed regarding the number of recreational hours per week they spent on the internet. In general, the researchers found, as internet use climbed, so did BMI, particularly among girls younger than 18 years old.

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