The short answer: exercise! Physical activity can help you increase your amount of lean muscle mass, which has been shown to have a number of health benefits, including fighting obesity and protecting against diabetes and insulin resistance.
A 2017 review in Advances in Nutrition noted that endurance and resistance exercises helped to preserve muscle mass during weight loss, and resistance training helps to improve muscle strength.
Exercise can help you maintain a healthy bone mass level, too.
Our bones tend to deteriorate as we age, and there is also a reduction in bone formation. This can lead to osteoporosis, which can increase the risk of dangerous falls and fractures.
A report in Therapeutic Advances in Musculoskeletal Disease notes that physical exercise can help, citing studies that show that activity can improve bone mass, and even prevent bone loss in women.
You may also want to reduce excess (storage) fat, especially around the belly.