I think the parent comment was implying that jam can be healthy just because it uses whole fruit as an ingredient. The chemistry behind turning a mixture of fruit and sugar into something called jam is pretty well known - there has to be a certain ratio of sugar for it to "set". Usually this is 1:1.

I wrote my comment because I think that people are shocked when they actually see jam being made at home and how much sugar goes into a batch.

https://www.compoundchem.com/2014/09/22/what-makes-jam-set-t...