Author's Note:

Firstly - Sherlock belongs to the BBC, Moffat and Gatiss - no copyright infringment intended!

More importantly - this is Post-Reichenbach Johnlock and involves food and weight issues.

The 'rules' John discovers aren't made up – they used to be mine. Needless to say this could contain triggers if you have issues with food as I wasn't in a good place in my life when I followed them.

This is a very self indulgent piece on my part, more cathartic than anything else, though I've written from John's perspective because I actually couldn't write much from Sherlock's – too close to home I guess! However the tone of this isn't dark and the ending is quite fluffy and positive.

So, if I haven't completely put you off, please read on

An Experiment and a Decision

If you'd told John three months and one day ago that he'd have got himself into this predicament he'd have suggested you might be, well, losing the plot a little bit. After all he knew how to take care of his own body, he was a doctor for God's sake and besides, Sherlock wasn't interested in him in that way. Heaven knows John wanted him to be but however strange Sherlock had been since he'd made his miraculous return it wasn't because he felt for John what John felt for him. No, John was just reading too much into the fact that Sherlock had missed his best friend while he was off dispatching Moriarty's goons and wanted to remain ... close. That was definitely all there was to it, nothing else at all, end of story.

Isn't it funny what a difference a day makes?

And yes, you're right - although that was hardly a difficult deduction, now was it - John and Sherlock have been together, in every sense of the word, for exactly three months. And you're also right that this story is about how they got from there to here. Here, by the way, being John standing in what used to be Sherlock's bedroom and is now theirs as Sherlock hovers in the doorway while they have a rather over-emotional conversation about, amongst other things, a pair of John's trousers.

But we're getting ahead of ourselves. Right now you need to know how they got together in the first place.

Unsurprisingly, given the level of denial John was in about it all, it was Sherlock who made the first move, choosing to announce his intentions in his own inimitable fashion. His method of courtship involved pinning John to the wall of an alleyway he'd dragged him into so they wouldn't be visible to Lestrade and his team, kissing him with an enthusiasm that almost made up for his lack of technique and only then saying "John, I seem to have become irrationally and irretrievably attached to you. I believe you feel the same but I would like to hear you confirm that."

John, once he'd got his breath back and decided that yes, that really had just happened, had replied "Yes, I love you too, you lunatic" and then proceeded to instruct Sherlock not only in the art of kissing but several other things that followed on from that. Sherlock had muttered, when his mouth wasn't otherwise occupied, that he hadn't really understood how John had come by the nickname "three-continents" Watson up until that point but now it all made sense.

Lestrade had also made reference to the nickname – although not in a complimentary way - when he found them; drawn away from the crime scene by a particularly loud cry John had wrung from Sherlock with his deliciously talented mouth and fingers. They were lucky the D.I. hadn't booked them for public indecency - and even luckier that they'd both finished by the time he got there - but they didn't get off scot free. Instead of taking themselves back to Baker Street for hot showers, sleep and more sex - definitely not in that order - they found themselves, on pain of their antics being shared with the rest of the world in general and Anderson in particular, returning to the Yard to assist in the other case Lestrade was working. The one Sherlock had refused to help him with earlier in the week, deeming it uninteresting and not worth his time.

By that point they'd been awake for over twenty four hours and, as they followed Lestrade down the corridor to his office, only the remnants of the endorphin rush he'd just had and the thought of the much needed caffeine injection he'd been promised was keeping John on his feet. When they passed a vending machine his stomach informed him that something more substantial than coffee would also be appreciated so he got a Mars Bar. Not healthy, not by a long shot, but right then he needed the sugar rush more than he cared about the calories. Jogging to catch up with Sherlock while he opened the wrapper John snapped the end off the bar in his haste. Not really thinking about what he was doing he offered the broken bit to Sherlock as they walked through the office door.

Sherlock had looked mildly surprised for a second, eyed both pieces suspiciously but then gave a small nod and allowed John to place the chunk on his palm. He didn't eat it though, not until John had swallowed his final mouthful but then he demolished it in two bites. Lestrade had given a John a very significant look - to be honest John thought it might have been the first time Greg had ever seen Sherlock eat - but when he spoke it was to ask Sherlock's opinion on a crime scene photo.

Thankfully the case had been easily solved – Sherlock had been right, it was uninteresting – and in the week that followed the flurry of sex, violin concertos and random discussions at odd times that constituted Sherlock and John becoming Sherlock AND John put the Mars Bar incident quite out of John's mind. Right up until Lestrade did something similar with a biscuit, that was, and Sherlock reacted as if the man had been trying to poison him.

By the time Sherlock had calmed down, John had apologised to Lestrade three times and Anderson and Donovan had run out of rude comments, John was gripped with curiosity. Whether consciously or not, Sherlock apparently had rules governing the acceptance of food and John wanted, no he needed, to know what they were.

Over the next month, thanks largely to a sudden surge in activity of the more cerebral of London's criminals, John had ample chance to surreptitiously test his hypothesis that while Sherlock would not eat when told to and certainly didn't seek food for himself while he was on a case, he would eat if food, possibly only food that belonged to John, was offered in the right circumstances.

What John discovered was this:

1. He was right about the food having to be his.
If it wasn't John's food, being handed over by John, Sherlock's reaction was … unpredictable was far too polite a term for it. John had only tested this with Mike and Molly but, given that he now a) owed Mike a new shirt and several pints due to an incident with a vial of iodine and b) had spent the afternoon following Molly offering Sherlock half of her packet of quavers holding a paper bag for her to breath into and then listening to her talk about Toby the Cat while she sobbed into his shoulder, he'd decided he didn't need any more data about that particular rule.

2. It had to look spontaneous.
The carrot chunks had been rebuffed, as had the slices of apple, both of which John had prepared and taken with him. Initially he'd thought it was the type of food being offered but then the end of a banana had been taken, as had a stick of celery from a bunch he'd bought from a market stall. The final test had been a carrot nicked from the kitchen of a crime scene. Sherlock had laughed when John waved it at him, made a reference to Bugs Bunny and eaten the end John handed him quite happily. John was so surprised that a cartoon rabbit had survived deletion he almost choked on his first mouthful; apparently Mummy had once likened Mycroft and his continual nibbling of sweets to Bugs and his ever present carrot and Sherlock had never been able to bring himself to wipe the memory of Mycroft's subsequent tantrum and Mummy's laughter.

3. The proportion mattered.
If he tried to hand over more than a quarter of whatever he had, Sherlock wouldn't take it at all, plus the next time anything was offered the item would be subjected to far greater scrutiny before it was accepted. Discovering this particular peccadillo had resulted in John consuming - amongst other things - the entirety of one of Angelo's garlic flatbreads as well as a bowl of Spaghetti Alfredo, the whole of a large Cornish pasty barely an hour after he'd had lunch with Mrs Hudson and quite a few bars of chocolate before he realised what the tipping point was. He'd surprised himself by being quite adept at hiding the fact he was uncomfortably full and more than a little pleased that his experiments had - due to the acting skills Sherlock was always telling him he didn't possess - gone unnoticed; he had no doubts that if Sherlock realised what he was up to his reaction would be more than a bit not good.

4. John couldn't ask.
If John actually asked Sherlock whether he wanted some of his food, as opposed to just physically offering it, the answer was always no. John could speak though; a meal at their favourite Chinese had solved that one. John starting by waxing lyrical about his ginger chicken before abruptly saying "Here," and plopping a large spoonful on Sherlock's plate. Sherlock made no objection, continuing to nibble on a wonton and make observations about the other diners but once John had spooned up the last of his sauce he'd picked up his chopsticks and delicately finished every scrap. He'd even added a spoonful of rice to it in order to absorb the sauce, although John was too mesmerised by his fingers sliding up and down the chopsticks to pay attention to that fact until later. Much later, after he'd taken Sherlock home and lavished those beautiful digits with as much attention as he could physically muster.

5. Acceptance didn't guarantee consumption.
Unless he was particularly distracted, Sherlock wouldn't take even a nibble of his share of the food until John had consumed all of his own portion. Considering John didn't often waste food he'd almost not noticed this rule at all but the few times they'd had to rush off somewhere and John had abandoned a snack he'd later found Sherlock's part tucked in a pocket or hidden somewhere else. He'd wondered, briefly, whether Sherlock had left his food for the same reasons John had but a few judicious "abandonments" later and he was certain. If John didn't finish his share, Sherlock wouldn't consume anything.

John knew he should have found the list concerning, after all it was concrete proof that his lover's relationship with food was far from healthy, but he didn't. It was all so … so Sherlock that he couldn't bring himself to worry about it. Besides, he was honestly more concerned about the alarming effect that their higher than normal case load, combined with the fact that they were - not to put to fine a point on it - shagging like extremely athletic rabbits at every given opportunity, was having on Sherlock.

The man was shedding weight he simply couldn't afford to lose faster than it was safe to do so and John was witnessing it at much closer quarters than he had ever done before. When he found that he could count Sherlock's ribs by feel through the material of his shirts, not just when they were in bed together, John knew he couldn't just hope the situation would fix itself any more. He couldn't stand by and let Sherlock damage his body any more that he already had, not now they were finally together, finally how they were meant to be. He couldn't lose him a second time.

Six months down the line, when John could talk about it all without burning with embarrassment, he would ruefully agree that he should have tried to talk to Sherlock first. Should have told him how worried he was, how much it hurt to see him shrinking before his eyes and apparently unconcerned about his own health. And Sherlock, after entwining their fingers and pressing a kiss to John's temple, would admit that, considering his past reactions to anything he classed as 'being told what to do' made Caligula seem like the model of propriety, John's fear that any discussion on the matter might generate hostility and more problems rather than help resolve the issue was perfectly reasonable.

And that was quite a round-about way of saying that John chose not to talk to Sherlock. He didn't tell Sherlock he was worried, didn't ask Sherlock to try and eat a bit more each day and he certainly didn't mention that he had noticed any change in Sherlock's body.

Instead he decided to try and get Sherlock's weight back to medically acceptable levels without saying anything to the other man at all. After all he knew the rules now, knew how to get Sherlock to eat without him getting upset, he could simply engineer what he ate to ensure Sherlock got sufficient nutrition from what John gave him. It was a win-win situation – Sherlock got healthy, John got to take care of him and no-one got distressed – practically the perfect plan.

Yes, you might well raise your eyebrows for all the good it will do. This is John after all, the man who killed for Sherlock twenty four hours after meeting him for the first time. When has he ever given any consideration to his own well-being when Sherlock was in danger?

This isn't my usual writing style so I would really appreciate and con-crit you can offer!