I just celebrated three years post whipple and find that I cannot properly process the vitamins and minerals that we would normally get through food; therefore I supplement with B12, Calcium, Iron, Enzymes (Pancrease) and have to have my potassium level checked monthly.
I also have plenty of yogurt and nutritional drinks on hand. I, too, lost a consideral amount of weight going from 205 lbs to 96 and now back to 112 with the help of lots of proteins and carbs.
I'm not lethargic but do require a "power nap" (usually a couple of hours) to get through a busy day.
Hopefully, all your husband will require is a little vitamin/mineral boost to get him back to his old loveable self;)