Yes, your blog can be put down on a college application. It counts as an EC for which you are investing your time and passion. If it’s an active blog with a relatively good amount of followers/subscribers, then I think it might be considered a good EC by adcoms. Of course, really, the quality of the EC is based on how much you put into it–if you’re putting a lot of effort into the blog, then it will show out. However, if you don’t post that often and it sits there collecting dust for weeks, it’s not really worth it to mention.
I don’t really know what a healthy lifestyle blog is (Sorry but that just seems like a broad term to me). Is it about like nutrition or more like about exercise? This may be obvious but just ensure that no inappropriate content is on the blog at all. If you’re going to be telling colleges about the blog, you don’t want them to see or read something that might throw up a red flag!