Human body fat is the most efficient way for a human to store energy. Give them enough (recycled) water, some vitamins and protein and they will shed weight all the way to Mars, and back maybe too.
Cryo sleep will not work, because joints will become fibrosed, muscles will atrophy, etc.
So to figure out how FAT our ASTRONAUTS will be - we'll need to look at some numbers.
A pound of fat can expend about 3500 KCAL of energy.
An average male basal metabolic rate is around 2000 KCAL/day.
Now using conventional fuel - the trip takes 214 days, using a constant propulsion nuclear motor might shorten it to 120 days
Soooo - ballpark FAT ESTIMATES are for conventional fuel 214 x 2000 = 428,000 KCALs
428,000 KCAL /3500KCal/fat = 122 pounds (or about 56 Kilos extra)
Nuke fuel require them to only gain about 70 pounds extra.
Now this is a one way trip - so lets double the weight to provide for our FAT ASTRONAUTS to get back home safely
So now we are looking at 244 pounds EXTRA - or a 444 pound (200 KILO) Buzz Aldrin... for conventional fuel
and for constant acceleration nuke powered craft - a 340 pound Buzz Aldrin
This will make the newer movie version of the RIGHT STUFF a bit different to watch. All those neck beards out there - yep - you're training for a MARS mission....