What's the safest way to treat bone loss?

Many options. First, find out the cause of the bone loss so you are not just treating the symptom instead of the cause. If you have osteopenia, make sure you maintain proper nutrition, keep active, do weight bearing exercises daily, take adequate calcium + vit d supplement (1200-1500 mg, 2000 iu vit d). If you have osteoporosis, do all above and a fda approved osteoporosis after discussion with your md/do.
Most medications. There are a number of medications specifically intended to treat osteoporosis. Your doctor will need to decide, with you, if and when you need to be treated and which of the available medications would be best for you.