Health and Fitness niche is really a profitable niche. You have many options to get quality backlinks.
At first, you must be careful producing high-quality content so that you can easily beat your competitors. You should write about trending topics in your niche. You have a good chance to get organic backlinks because organic backlink is a real backlink that you can get naturally if you have enough high-quality contents. People will link to your site when they find you are perfect and helpful.
Then try blog commenting. There are a lot of famous blogs that relevant to your niche. Comments on their posts.
Guest posting can be your best choice to increase your authority and trust level.
You can also try social bookmarking, forums posting, Q&A sites posting, directory submission and more to create high-quality backlinks.
Thanks.