I started a consumer SaaS almost 2 months ago. It's a calories counter system. You log in, register your meals and the system tells you how many calories you ate and the type of those calories. You cannot eat more than 10% of red calories, more than 35% of yellow calories and green calories you can eat as much as you like. It's currently free. The system now has around 3.6K users with something around 15% really active users and it is growing at a rate of 100 new users a day.
Any ideas, besides ads, on how to monetize this system?