Richard Weil from St. Luke's gives good 2 min advice on exercise
When I took the Lipidology boards the answer was 90 minutes of walking a day to maintain weight loss.
I am glad to see that Richard Weil points out, it has to be with a low calorie diet, just to maintain weight for the reduced obese.
His program doesn't start exercise till 8 weeks and then may start with resistance training of legs to prevent knee pain.
Once patient hits plateau he uses individual Rx of exercise for what works for the patient.
This is how I interpret what he said at the Obesity Board Review 4-15