You wouldn’t have prevented it. You would have maybe unknowingly created a condition that would have postponed it. And then you would never have known that you had done so.
In any case, obesity is the result of a lifestyle and going on the hike was a choice that he made and that his daughter accepted when she chose to go on the hike with her father knowing his condition.
Tragic, but there it is. The clock is ticking for us all. Any day now.