I think at first focus on one tight niche, ie the weight loss, and work on getting the conversions happening there initially. You could do something like adding in your process a questionaire which asks about various other health issues that overweight people are likely to have. From that send specific email series about that condition for a particular product in your lineup, with a new target customer focused on that issue.
I have a similar dilema of one product with multiple target markets (sports, detox, general health/anti-aging etc) but I’m going to focus on one specific customer avatar for now. At the beginning Jim talked about focusing on one business, getting that working, and then duplicating the process. I think the same can apply in our general business with multiple products/customer bases, focus on one aspect of it and then repeat the process.