On more than one occasion, for an extended period of time, I have had as many as five teenaged males in my household. I have had to "reel" in their "grazing" on numerous occasions! They were all very active in sports and their appetites were a reflection of their activity!
I have never been a purchaser of convenience foods or junk-type fillers. We did not purchase cold cereal as a breakfast food--I cooked eggs, pancakes, homemade biscuits, etc. for all of the kids who lived with us. I found that, by filling them with a good hearty breakfast, I could keep them out of the kitchen and the cupboards!
After saying all of that, I never had to put my kids on a food budget. Whatever I fixed, they gladly consumed! But...my kids were not allowed to complain about what was served/provided. When you grow up in a large family, you learn to be THANKFUL that you get called to the supper table! Consequently, you learn not to belly-ache about the food, 'cause someone else will GLADLY eat what you don't want! And....they helped by hunting/fishing and putting some meat on the table. They also had to help with harvesting, canning, food preparation, butchering, perusing the sale papers, purchasing groceries, etc. and were well-prepared for purchasing their own groceries when they left home.
I am all for teaching kids lessons that will prepare them for real life. I think this mom had tried every other way to get her message across to this son. I see no harm in allowing him to learn TANSTAAFL, which stands for There Ain't No Such Thing As A Free Lunch! Miss Paula in Texas