"Are you hungry?" John asked Sherlock.
"Nope," he said hurriedly. John had hid his cigarrettes again, so he was frantically trying to find them. Right now he was in the process of pulling all the books off the shelf.
"Are you sure? And would you stop pulling all the books out of the shelf?" He pleaded. "You’ve been doing so well while trying to quit-"
"Well now I need them!" He exclaimed. He was pacing around the room, as all of the usual places John usually hides them had been searched and without any luck of finding a pack.
"You know in all the years I’ve lived with you, I don’t think I’ve ever seen you eat," John mentioned. "Why is that?"
"I’ve grown immune to going long periods of time without eating," he answered. "Now where are the cigarrettes?!?"
"Just a moment," John said, thinking about what he just said. "Immune to it? How?”
Sherlock gave a long, heavy sigh. “You ever wonder why Mycroft is so fat?” He said in a serious tone, which made John smile.
"Uh, no, not really," he admitted.
"Nor why I never eat?"
"I do think about that a lot," John admitted.
"Ever think there’s a story behind it?"
"Well there is," Sherlock said. He seemed ready to tell a long story. "When I was a kid, maybe eight or nine, mother was unemployed. We were already really poor, and one night dad came home and he seemed real depressed. But he didn’t say anything, just sat down for dinner. There wasn’t much, just some bread.
"After dinner he sent Mycroft and I up to the attic, which is where our bedroom was-"
"Our?" John asked in disbelief. "You mean you and Mycroft use to share a room?"
"Yes, John, Mycroft and I used to share a room. Anyways it was really cold up there, so it was hard to try and get to sleep. Since we couldn’t sleep we heard mother and father talking. Apparently that day father had lost his job, so now getting by was going to be even harder."
He left out the part about him and Mycroft sitting up all night talking, trying to figure out what to do, and eventually Sherlock just fell asleep, so Mycroft gave him his blanket and forced himself to stay up to keep an eye on his little brother.
"So after a while, as you can guess, we lost the house and we were living on the streets. Father and Mycroft developed anemonia. Mycroft got better, father… didn’t.
"Mycroft developed this habit of overeating whenever food was available, since he didn’t know the next time any of us were going to eat. I just quit eating, beginning to grow immune to the feel of my stomach growling. I guess I never really got over it."
John was silent. He didn’t know what to say. “Sherlock, I-“
"I know what you’re going to say, John, you’re sorry," he muttered. "But it’s not your fault. It’s over with," he seemed pained by talking about it. He stood up and, without another word, walked to his bedroom.
It’s not very long, but here you go. Sherlock fanfic. @shadythealpha