.. the biggest offseason struggle they have is maintaining weight.
They have lifting/conditioning every morning (that includes agility). They will also lift/train multiple times throughout the day (visit a Vasa or other gym around Provo/Orem at night and you'll find a few OL/DL guys).
Muscle burns more calories than fat... Keeping a 'svelte' 6'(6" - 8") 320lb figure requires a massive amount of fuel. You drop 10lbs and you'll spend the next few weeks getting yelled at.
Food is the struggle of the o-line offseason.