A careful balance of fat and muscle is needed to keep bones strong and healthy as people lose weight, says a new study.The research, by scientists at Nottingham Trent University, the University of São Paulo and Robert Gordon University, highlights the importance of controlled weight loss involving both diet and exercise. Published in the journal Nutrition Reviews, researchers found that while the total amount of fat was linked to greater bone mineral density in overweight people, bone health worsened as fat mass increased relative to their muscle mass.