John could remember very well the first time he'd become aware that beneath all that incredible deduction hocus-pocus and hard exterior, there might be somewhat of a problem.

A problem with Sherlock Holmes.

A deadly problem.

It was during their first case together, which John had aptly named 'A Study in Pink.' The two of them had been staked out in a restaurant, waiting for the killer to show up. The entire experience may well have been abundantly awkward, but that wasn't what John was trying to focus on now.

He'd rather not remember that part, honestly.

As soon as the menus were placed in front of them Sherlock had immediately moved his aside, as if it were some kind of useless annoyance, or—as John now pondered—perhaps vaguely threatening.

"You may as well eat. We're going to be waiting a long time."

"Hm... You going to?" John was too busy looking over the menu to glance up at him, distracted by how hungry he was and how appetising everything looked.

"What day is it?"

The question did seem random and out of place, but John didn't really take much notice. "It's... Wednesday."

"I'm okay for a bit."

"Wha—" John stopped reading and looked up at him finally, not meaning to raise his voice, but not really caring anyway. "You haven't eaten today? For god's sake, you need to eat—"

Sherlock still wasn't looking at him, instead keeping his eyes fastened on that bloody mirror in the back, thereby watching the road behind him. "No, you need to eat, I need to think." He leaned forward and set his elbows on the table, steepling his fingers. "The brain's what counts, everything else is for transport."

John would have argued further, but at that moment the waiter arrived at their table again, settling a candle in between them. He could only look up and then across at the man on the other side of the table, who apparently had not and was not going to eat today.

"...You might consider refuelling."

This got him no concrete response, and he felt rather pressured to give up on the subject.

But he hadn't given up thinking about it. Nor had he come any closer to understanding Sherlock 'I don't need to eat yet because it's only Wednesday' Holmes.

Unfortunately, that hadn't proved to be a one time thing.

It seemed to be Sherlock's routine to go for days at a time without food of any sort, and usually with no break in activity, so that the doctor wondered how on earth he wasn't feeling the effects.

The only conclusion he could come to wasn't very reassuring.

That he did feel them—the fatigue, the aching hunger, the dizziness and light-headedness, the general discomfort—and just ignored them all and kept pushing.

Perhaps some of the symptoms would be dulled from a long time of experiencing them, but that was no better.

That just meant he'd been starving longer.

And that he didn't care.

Even off cases, it took John nearly forcing him to eat. Not in the sense that he had to grab his face and force-feed him—thank god—but that he had to be the one to do the shopping, and the cooking, and put the plate in front of Sherlock, along with a few reminders, before he'd eat it.

It worried him, sometimes. He would mention it, off and on, and the response was always the same:

"I don't eat during cases. It slows me down."

Or:

"I just need to think. The body is transport."

Transport or not, that didn't seem to John like a valid reason to fast for three days in a row while still dashing up and down staircases and running all about London, jumping fences and leaping down balconies. All the while hardly sleeping, either.

The man had to faint sooner or later.

But it seemed he usually toughed it out and pushed through as long as it took, running on pure caffeine, nicotine, and adrenaline, so that by the end of a case he would so knackered that all he could do was collapse on the sofa, fully clothed in coat and scarf and shoes and unable to do much more than sigh.

By the next day, though, everything seemed to have started over again. Sherlock's inner clock seemed to be reset, and he would be off looking for another fix.

Another case that would not only satisfy his appetite for excitement, but also his lack of appetite. A good reason not to eat.

An easy reason.

A convincing one.

And all the while having fun in sufficiently dangerous situations to keep him content. To prove he was clever.

All this John could only watch with slight concern for his friend. There were things he wanted to say, things he wanted to do, but Sherlock did not seem open to change.

He didn't seem to care enough that he was starving to do something about it.

Unless...

...That was what he aimed for.