To whit: I run a men's lifestyle Q&A site. I have a total of 25 categories in which questions are submitted. Currently, however, these categories are in fact sub-categories, such that Bodybuilding, Cardio, Nutrition, Health and Sports for example, all belong to the Health & Body meta category, of which there are 5 in total. Is this the best structure for the site, or would it be better for SEO to upgrade the sub-categories (since there are - and probably always will be - only 25...) into full-blown categories? Thanks very much in advance for any light you're able to shed on this. 
What is the optimal way to apply categories to a new site?
seo;sitemap