Thanks for pointing that out. The ranking system is a multi-dimensional algorithm that optimizes for a variety of micro and macro nutrients. Individuals with different dietary needs have different star representations / health scores for the same meal. For example for someone with hypertension that chicken sandwich will have a very poor health score.

notahacker raised an interesting point about not being too harsh. Some people could benefit a lot if they cut down from a burger, fries, and a large soda to a chicken sandwich and a diet soda. If you rate the chicken sandwich 2/5, your site will just depress them. On the other hand, a knowledgeable person with aggressive goals wouldn't trust your site if you gave that chicken sandwich a higher rating. Have you thought about making the ratings relative to a person's current dietary standards?

The ratings are currently personalized to each users nutritional profile that is created at the end of the sign up process. Our detailed sign-up process resembles a health risk assessment in which a user has to answer questions about past and existing diet related chronic diseases like diabetes and coronary artery disease.

The ratings also depend on prior choices made by the user. This means that the same meal may have a different ratings for lunch and dinner.

that's a fair enough answer. It'll help the usefulness of the app massively to be able to compound the effects of particular meal combinations over the course of time (not least to give committed users a reason to keep returning and updating their details).