ok to eat junk food?

say you ride, oh, 26 miles a day.

according to some calculations, that would be roughly 1300 calories
needed just to power the bike.

is it ok to eat what would normally be considered junk food,
to get these calories?

assume the daily requirements of vitamins, proteins,
minerals, etc are met by other, decent food. and assume you don;t want or
need to lose any weight.

i mean, don;t the muscles run on sugar? what would be wrong with getting
the extra calories right from sugar?

what about fat?

just wondering,
wle.