Women are getting fatter because they've cut back on the amount of chores they do, controversial research claims.
They are burning up to 360 calories less a day than their parents did because they are so sedentary around the house.
Women have also used the hours gained from time saving technology like washing machines to spend twice as much of their lives sitting watching TV than they did in the 1960s.
The findings are likely to outrage working mothers for whom there is still a gender imbalance when it comes to housework.
Despite advances in women's rights in terms of pay and conditions, in many cases they are still doing the bulk of the cooking and cleaning.
The study was carried out in the US by Edward Archer, a research fellow with the Arnold School of Public Health at the University of South Carolina. Similar studies have also shown the same result.
He studied thousands of "time-use diaries" provided by American women every year beginning in 1965.
He found that back then women spent an average of 25.7 hours a week doing the laundry, cooking and cleaning.
In 2010 things had changed and women were spending an average of 13.3 hours per week on housework.
A recent survey by npower in the UK found a similar trend.
On average women now spend 18.2 hours a week on housework, including cleaning, vacuuming, food shopping and cooking.
This compares to 44 hours a week on average in 1965, according to official figures from the Department for Education.
Dr Archer found that as a result of the change, housewives were burning around 360 calories every day - more than the typical chocolate bar - less than they did in the 1960s.
Working women burn about 132 fewer calories.
In a depressing twist, with all that extra time in their lives women have apparently used it to sit down and watch TV.
Dr Archer found that in 1965 women typically spent eight hours a week catching up on their favourite programmes.
By 2010 that had more than doubled to 16.5 hours a week.
Dr Archer said that the overall trend was to "large reductions in energy expenditure".
He concluded that women needed to "start finding ways to incorporate movement" into their daily routine such as walking to the post box, chopping vegetables or playing with the dog.
In Britain, research shows that women are still doing more around the house than most men.
According to one study from Oxford University, if current trends continue women will have to wait until 2050 before men are doing an equal share of the chores.
Feminist and relationships expert Jean Hannah Edelstein said it was a "preposterous, sexist assumption" to suggest that women should do more cleaning to slim down.
She said: "It's not like men are getting any thinner either - perhaps they should get off their behinds and do some more housework!"
- DAILY MAIL