My High School Ranger Best Friend said he lost 21 pounds doing the Ranger school, because he was patrolling an average of 22.5 hours a day for 12 weeks on a single MRE every 36 hours and a full canteen meal every 4th day, they 're probably at no more than an average of 1.2 to 1.5 K Cals a day with a constant burn of bodyweight.
The SEAL BUDS school has the additional factor of thermal caloric loss to the cold water, those are some rough, tough, dedicated Mofos , that 's a seriously painful ordeal. On pure body compisition though, swimming is more retentive than the open air burn of running, a triathlete like Brodus understands the dynamics involved here better than I.
As I understand it, the practice is to fatten and muscle up some before one does the schools, in order to keep sufficently able down the stretch.
Proteins, Creatine, Carbs Packs, Adaptogens, Prohormones like M4OHN, you name at are in use in the US Special Ops groups, and the requisite candy, Advil, is being popped freely as we post.