Researchers may have discovered the key to avoiding obesity - live on your own.

An American study found that women living in households with four or more people were significantly more likely to be obese than those who lived by themselves.

Married women were also more likely to be obese than those who remained single, according to research published by health journal BMC Family Practice.

Cheaper food, lack of exercise and the increasing "couch potato" culture in the UK have been blamed for a rising number of people becoming overweight or obese.

The latest research, conducted by researchers from Texas Tech University Health Sciences Centre, questioned almost 300 women who attended family planning clinics.

Almost half of the women (47.8%) were classified as being obese - defined as having a body mass index (BMI) of over 30.

But family circumstances appeared to play a role in determining whether women were obese or not.

While only 32.5% of those who lived alone were obese, this rose to 64.8% of women who lived in households of four or more people. They also found that 44.7% of people who lived with one or two other people were obese.

Married respondents were also more likely to be obese than unmarried people - 58% compared to 42.5%.

Over 60% of women who did not have a high school education were obese, compared to only 40% of those who went into higher education.

The researchers, led by Professor James Rohrer, also found that women who received no support from their parents were more likely to be obese than those who received a lot or some parental support - 52.8% compared to 42.7%.

"The reasons why large families increase the risk of obesity are not entirely clear," Prof Rohrer said. "One obvious mechanism is that larger households are more likely to have greater volumes of food available."