I bet you could detect a lot of candy buyers through their patterns of convenience store purchases. There's also candy stores, fast food, and restaurants that are known for rich food. Machine learning could probably figure out a lot if trained on the confirmed habits of other people whose purchase records are available. You could do customer surveys to get the data, or put what you want to know into the intake form.

What I don't buy is that people's habits will generally predict their health situation. I think this is a report on a press release of what some medical business association imagines that the person that they're hoping to recruit from somewhere will be able to do. I think the benefits will end up far lower than the costs.