Increasingly, a heavy morning meal like ham and eggs wasn't considered ideal for health reasons. Diseases such as tuberculosis (then called consumption) plagued many Americans at the time. So did digestive ailments, likely linked to a typical diet high in refined carbohydrates, sugar and meat. what is the topic?

The topic is: diseases/illnesses in Americans eating certain foods.

the purpose of the heading in the passage is to identify who is telling the story.

this excerpt is part of the book sugar changed the world (2010) written by marc aronson and marina budhos. as the book has been written by two people, the heading "marc" indicates that this specific excerpt is being narrated by aronson. in the fragment, marc describes his grandfather's story after hearing it from his cousin. however, there are other excerpts where budhos is the one that tells the story of her family.

aronson and budhos, who are husband and wife in real life, decided to write sugar changed the world when they found out how sugar, which had an important role in slavery and economy, changed their ancestors' lives.