Let's say that I have a main niche (e.x. weight loss) with 3 subniches related to the main niche ( e.x. healthy nutrition, fast diet, diet reciepis) Which is better: 1) To build one site (e.x. weight-loss.com) and to write articles about the main niche and the subniches? 2) to build four different sites ( ex. weight-loss.com, healthy-nutrition.com , fast-diet.com ...) and to write on each of them related stuff?