A study at the University of Pittsburgh Physical Activity and Weight Management Research Center reports that women who exercised 275 minutes per week (1835 kcal activity energy expenditure) showed a weight loss of 10% or more of initial body weight at 24 months of training.
Four behavioral weight loss groups were studied (201 overweight & obese women):
Physical activity energy expenditure: 1000kcal/wk with moderate intensity
Physical activity energy expenditure: 1000kcal/wk with vigorous intensity
Physical activity energy expenditure: 2000kcal/wk with moderate intensity
Physical activity energy expenditure: 2000kcal/wk with vigorous intensity
All participants were told to reduce food intake to 1200 to 1500 kcal/day. The BMI (Body Mass Index) range of the women was 27 to 40 kg/m^2.
The research team led by John Jakicic concluded that the addition of 275 mins/wk of physical activity, in combination with a reduction in energy intake, is important in allowing overweight women to sustain a weight loss of more than 10%.
Source:
Jakicic JM, Marcus BH, Lang W, Janney C. Effect of exercise on 24-month weight loss maintenance in overweight women. Arch Intern Med. 2008 Jul 28;168(14):1550-9; discussion 1559-60.