Well, for one thing, people differ genetically. Some think that Europeans were hit with a wave of Type 2 diabetes in the 17th-early 18th century, when prosperity made it possible for just about everyone to have white flour and sugar. The massive die-offs from the Type 2 diabetes that resulted made it so that Europeans who survived (some of whom emigrated to America) were the ones who had *less* "thrifty genes" - and thus less tendency to Type 2 diabetes than did the Africans or Native Americans.
Hispanic people aren't uniform, either - some have more Spanish, some have more Indian, some are a mix of Spanish-Anglo-Indian