The boys are not starving, but they are eating an incomplete diet that often makes them sick, and they are always desperate for meat.
Although the island has a lot of fruit trees, the boys want a pig. The “seductive, maddening” promise of meat is ever-present. They assign a group of boys as hunters, led by Jack.
The kids spend a lot of time eating, actually. They mostly eat fruit from the trees. Ralph complains that the kids are not doing what they were supposed to do, but instead spend their days fooling around and eating.
“We want meat—”
“And we don’t get it.”
Now the antagonism was audible.
“But I shall! Next time! I’ve got to get a barb on this spear! We wounded a pig and the spear fell out. If we could only make barbs—” (Ch. 3)
Because the boys eat so much fruit, they often have diarrhea. This is especially a problem for the youngest boys, called littluns, because they do not have the best sanitary habits. The older boys mostly ignore them and leave them to get sustenance on their own.
The boys do eventually get the pig. There is a schism that results in Jack and the hunters going off on their own, no longer submitting to Ralph’s leadership. Jack has the meat, and invites the others to have some in order to show it off. Ralph doesn’t want to go, but the meat is tempting.
Ralph’s dribbled. He meant to refuse meat, but his past diet of fruit and nuts, with an odd crab or fish, gave him too little resistance. He accepted a piece of half-raw meat and gnawed it like a wolf. (Ch. 4)
When Ralph is finally rescued, he is very hungry. The boys have been subsisting on fruit for too long. They may not be starving, but they are not healthy either.