A/N: A lot of theorizing on my end as to why Luffy eats so damn much.

I assume that if you're reading this you're already aware of spoilers in fanfiction, and either already know them or don't care.

"That's it! I've had enough!"

The shout rung loud and clear across the ship, and every single person on board immediately stopped whatever they were doing to look over their shoulders towards the loud frustrated scream. It had come from the Mugiwara's navigator, none other than one 'Cat Burglar' Nami. The reason for her evident irritation was not yet known to the crew, but a few of them had an inkling of what it could be.

"Wow, she sounds really angry this time," Usopp commented, an involuntary shudder traveling up and down his spine. He pitied the poor sucker who would be on the receiving end of that fury.

When Nami barged from her study, looking absolutely pissed, scanning the deck with narrow eyes, Usopp decided that the poor sucker would probably be dead in the next five minutes. In which manner, Usopp had yet to determine.

"Luffy!" she screeched, her teeth sharp and weapon already in hand.

Nice knowing you captain, thought Usopp.

"Nami-swan looks so beautiful when she's angry!" spurted Sanji, before becoming serious again as he glanced over at a puzzled Luffy as he sat on Sunny's figurehead. Everyone in the immediate area gave their leader a raised eyebrow, wondering what the hell he had done to set their navigator off this time. Even Brook, Chopper and Franky came to see what was going on – Franky from below deck, Chopper the infirmary and Brook the crow's nest.

Their rubber captain, realizing that he was being called, launched himself from Sunny's mane and landed on the deck before Nami. "Yeah?" the rubber-man asked, blinking owlishly.

"We're running out of money here because you," she emphasized it by pointing sharply at him, "Eat far too much!"

"But I get hungry!" the Luffy whined pitifully, sticking out his bottom lip, completely unconcerned about his eating habits.

He acts like such a child sometimes, Nami thought with a huff and smacked him upside the head. Luffy gave a pained sound and clutched the stinging bulge. "I don't care! No normal person should eat that much!"

"But Nami–"

"Don't 'but Nami' me!" she barked. Shaking her head in exasperation, she pushed a strand of her hair over her ear, "Sanji-kun, could you do me a favor?"

"Anything for Nami-swan!" the cook crooned.

"Only make a normal person's serving for him from now on, please."

Zoro, Usopp and Chopper decided to join in when they overheard the gist of the conversation. "Oi, Nami, don't you think that's a little harsh? I mean, sure, we spend a lot on food, but we can always steal gold from other pirates or catch a Sea King or something," Usopp said in defense of his captain. To Luffy, missing a meal was even worse than death.

"Yeah, give the guy a break," Zoro added. Knowing Luffy the longest, he was well aware of the boy's monstrous appetite.

Just as expected, poor Luffy looked absolutely horrified, as though it was a death sentence. "No, it's not. I'm being perfectly reasonable. Luffy, if I catch you stealing from other people's plates, I'm going to lock you in the men's quarters and you won't be getting anything," Nami growled.

That shut him up all right.

Chopper looked a little uncertain with the matter, but brushed it off for the moment. He knew that if anything was wrong, he could fix it. But he still had a nagging doubt that this would end badly.

The first day had everyone wishing that they had more money. It wasn't that they had to defend their plates even more than usual – in fact, it was surprisingly quiet for a meal on Thousand Sunny. Everyone was nearly silent, a few having hushed conversations while eyes glanced around at the rest of the crew. The tension was so thick that it could easily be cut with a knife.

The source of the tension? Luffy, of course.

He was on his best behavior, fearing that Nami would go through with her threat of locking him in the men's quarters while everyone else ate. Already the boy had cleaned his plate and licked the last bits of food residue in a vain hope to sedate his gnawing hunger.

But it wasn't even that that was bothering everyone.

It was Luffy's pitiful expression as he slumped in his seat and massaged his stomach. His eyes were staring at the other's food pleadingly like a starving dog. The worst part had to be the frequent rumbling noises emanating from his belly, accompanied by his staring.

It was safe to say that everyone pitied him at that moment, including Sanji, who wouldn't give the poor guy any extra, because despite feeling sympathetic towards him (the man knew how it felt to be so hungry that moldy food looked appetizing), Nami-swan gave specific instructions not to.

That is to say, everyone except Nami pitied him, who spent the entire evening in good spirits.

Devil woman … Zoro thought as he watched Luffy try to act like he wasn't extremely hungry the next day. His captain still ran around and played with Usopp and Chopper, but the green-haired swordsman couldn't help but notice that Luffy seemed to pause when he thought nobody was looking and scowl at his own stomach – and then he would pout when it growled again.

"Cook, you sure Luffy'll be alright?" Zoro asked the man in passing.

Sanji paused and looked over at Luffy before turning back to the swordsman, "He should be. I make his food with lots of calories, so I wouldn't worry too much. Despite being a freak, he's still human."

He sounded a little doubtful. It seemed as though Zoro wasn't the only one who noticed.

The first sign that something was going on was when Luffy started getting tired in addition to being hungry. Practically everyone on the ship had caught Luffy napping when he normally would have been bouncing around the ship in search of something to do. The lethargic actions and dark circles under his eyes were quite noticeable.

It was … concerning, at the very least.

And then came the time that Zoro was forced to drag a half-awake Luffy from his bed by the ankles at one in the afternoon.

It was also notable that Luffy would get tired during fights, and because of this he made stupid mistakes. One such mistake nearly got him killed by a Marine when they were being attacked. His reaction rate had gone down and their enemies took advantage of Luffy's handicap. It was an unspoken rule that those closest to Luffy had to keep an eye on him and in the event of an attack, and fight back to back with him so that he wouldn't accidentally get stabbed.

Even Nami started to take notice, but instead of admitting that it was the lack of food that caused the distress, she told him to go to bed earlier, all the while biting her lips in hope that she was right.

The next was the grumpiness.

Yeah, when Luffy was mad he would shout and growl, or sometimes act like a child and go sulk angrily, but never in any of their memories had any of them seen Luffy acting bitchy. Hell, he had even snapped at Franky when the cyborg said something that the captain wasn't too inclined to hear.

The mere mention of food or Luffy's strange behavior was now off limits. They had been given the 'evil eye' on more than one occasion now, and the expression had scared Usopp and Chopper shitless.

Meals were painful even, for everyone.

But, no, Nami had her pride to uphold and guiltily prodded at her plate during mealtimes. Everyone, including Sanji, hoped that she would let go of her stupid pride for once and just let the poor boy eat.

Chopper was starting to get worried. Luffy looked thinner than usual. He was also paler to add to the fatigue and mood swings – all symptoms of malnourishment.

So when came the night that Luffy was actually missing for supper, everyone panicked.

Nami was the first one to notice, and was immediately on her feet to search for her rubber captain. Everyone else pitched in, temporarily forgetting about eating and focusing on their leader's welfare.

After a few minutes of fruitless searching and a dust bunny colony in Usopp's hair, they found him huddled up in his blanket on his bunk, head underneath the covers and hugging himself. At first they thought he was asleep, like he had been inclined to do the last few days. However, when Luffy's hands shot out from under the blanket and yanked up a bucket that had been on the floor, and then dry retch several times into it, everyone became rather alarmed.

He was sick. Luffy was never sick.

Nami was at his side instantly, massaging slow circles in his back as he tried to throw up his own stomach. Chopper then stepped forward, hopping onto the bunk to examine the sick man. Luffy's skin had taken on a pallid hue, tinged with a sickly green and yellow color, his eyes were unfocused and drooping, shaking from a cold sweat, skin hot to touch.

Chopper's grim frown matched the others in the room. They didn't even need the doctor's diagnosis to know what was wrong with him.

Nami felt incredibly guilty in that moment.

"You guys should all leave the room," Chopper said, to which no one objected. Nami stayed by her captain's side, still rubbing his back as he hugged the bucket. There wasn't even anything inside his stomach for him to throw up it seemed.

"I'm sorry," she whispered, "This is entirely my fault."

Luffy glanced over at her and gave a small smile, "I forgive you."

The sweet moment was ruined by another round of retching.

While Luffy was … occupied, Nami turned to Chopper. "What's wrong with him, anyway? I wouldn't think eating normally would hurt him."

The small doctor spoke hesitantly, perturbed, "I'm not exactly sure about this, but I think it has to do with his Devil Fruit powers."

Nami blinked before tilting her head in confusion, "How so?"

"Well, for most Devil Fruit users, using their abilities is as easy as thinking about them," Chopper looked a little unsure and frowned as he spoke. "Paramecia powers are usually all over the place; they don't really have a set of specific characteristics. Luffy's abilities affect his body directly. Even unconsciously, he can stretch; he doesn't even need to think about it - his body is literally made of rubber. So I think that stretching may take energy."

"It takes up energy?"

He nodded, "Yeah, like running or lifting weights, stretching probably takes up energy too. Not to mention that he more or less throws punches in fights, or he'll use his body like a slingshot. Have you ever noticed that after fights or some other heavy activity he'll eat more and sleep deeply?" Now that it was mentioned, Nami had noticed it (that being a cause for annoyance in the past). "Luffy is also very active, and his metabolism is high. For someone so strong, he's quite thin, don't you think?"

"Yeah, I guess so," she said quietly. Once or twice Nami had wondered how such a small person could easily break down walls, create craters in the ground and knock people out with a single punch.

"He's also used to eating so much, most of it high-protein meats, which is probably a habit developed when he was very young. His body can stretch to accommodate the amount of food he intakes, and then he'll shrink down very quickly."

"You mean he absorbs all that energy from the food within a few minutes?"

Chopper was wearing his doctor face now, "Yes. What's probably going on right now is that he's been burning more calories than he digests, and his body, used to eating so much, and having burned out any stored up energy, has been tricked to think that he's starving. He's sick right now because his stomach is over-sensitive and his weakened state is starting to really affect his health."

"I'm so sorry, Luffy," she apologized again to him.

"I'll go get some medication to calm his stomach. After that we'll feed him little bits until he can keep something down. Once he can eat properly again we'll ease him back into his normal routine."

"That sounds great Chopper, I'll keep an eye on him for now," Nami said to the reindeer, who nodded his head before jumping off the bed and heading to the door to fetch the medicine and explain the situation to the other crewmembers (who were undoubtedly just outside the door).

"You don't have to stay in here Nami, I'll probably throw up all over you," Luffy said with a dry chuckle.

Nami shook her head, "This is my fault, so I'm going to make sure you get better, all right? I don't care about your food bills anymore. We can find some other way to fund your bottomless pit. You're more important."

"Thanks for worrying about me, Nami."

Chopper came back after a while to have Luffy take the medicine, which really seemed to work fast, and work well. It wasn't too long before the Captain started getting drowsy, and now that he was more comfortable was able to doze off. Nami stayed by his side the entire time.

That was the last time that anyone complained about his diet.