To kill Stu "because he's contaminated" and then eat the radioactive Stu stew doesn't make sense. But Stu wasn't really contaminated. Ms. Mead says later she can turn the Geiger counter to beep like that. Stu was only killed on purpose.
Despite being on an extreme calorie-restricted diet for 18 months, none of the survivors appear to have lost an ounce of weight. Obviously the entire cast could not be placed on a starvation diet to exhibit weight loss but their clothes all still fit properly.