If we focus on the grammar first: "those" is a pronoun and "fortunate" is an adjective that refers to the word "those". If we focus on the meaning then in this example sentence it might be that "those" means "people who for one reason or another have limited access to food". But I think if we are talking about fasting during Ramadan I think it's also possible to say that it's not just people who don't have access to food, because: 1. People fast in other ways (not just food) 2. The process is intended to make people reflect on their position (how fortunate they are compared to others)

a phrase "those less fortunate" works as a noun here