MedWire News: Overweight and obese women may need to exercise 55 minutes a day for 5 days a week, in addition to restricting their calorie intake, to sustain a weight loss of 10% over 2 years, research indicates.

More than 65% of US adults are overweight or obese, which significantly increases their risk of heart disease and other related conditions," explain Dr John Jakicic, from the University of Pittsburgh in Pennsylvania, USA, and team.

They say that current guidelines recommend 30 minutes of moderate physical activity on most days of the week, for a total of 150 minutes a week, but add that "a growing consensus suggests that more exercise may be needed to enhance long-term weight loss".

To investigate further, the researchers enrolled 201 overweight and obese women in a weight loss programme between 1999 and 2003.

All the women were asked to limit their calorie intake to between 1200 and 1500 calories a day. They were also assigned to one of four groups based on physical activity levels and energy expenditure.

The participants were also asked to attend group meetings focusing on ways of modifying eating and exercise habits and were asked to keep in regular contact with the researchers.

After 6 months, women in all four groups had lost an average of 8-10% of their initial body weight. However, most of the women were not able to maintain this level of weight loss and, after 2 years, the women's weight was an average of 5% lower than their initial weight, with no difference between groups.

The 25% of women who maintained a weight loss of 10% or more over the 2-year period expended an average 1835 calories a week and exercised for 275 minutes per week. These women also followed dietary recommendations for weight loss more often than the other women.

"This clarifies the amount of physical activity that should be targeted for achieving and sustaining this magnitude of weight loss, but also demonstrates the difficulty of sustaining this level of physical activity," Dr Jakicic and team write in the Archives of Internal Medicine.

They add: "Research is needed to improve long-term compliance with this targeted level of physical activity. Moreover, continued contact with the intervention staff and the ability to sustain recommended eating behaviours also may be important contributing factors to maintaining a significant weight loss that exceeds 10% of initial body weight, which suggests that physical activity does not function independently of these other behaviours."