Natasha had noticed it first. The fact that Steve ate food.

A lot of food.

Like, he was constantly chewing on something. In fact the only time he didn't seem to be snacking was during a mission or a briefing. And afterwards he would practically shovel food into his mouth. He always ate everything off his plate and often finished everyone else's leftovers as well. Restaurant owners loved it when the Avengers came by for a bite to eat. Between Thor and Steve there was never anything left to take home for later and by the time they got home Steve had his head in the fridge, looking for something else to eat. And yet, he never gained a single pound in his ongoing quest for food.

It never occurred to her why he ate so much until Bucky moved in.

Bucky, it seemed, had the same penchant for food though his cravings had more the feel of starved wolf than Steve's grazing horse sort of attitude. Bucky would take the food he was offered and guard it, chewing and swallowing so quickly one only need to blink twice in the time it took for him to finish a meal. He eventually slowed down to a more human level as he became more mentally and emotionally stable but he still ate enough food to rival and possibly surpass Steve. The fridge was always empty.

It took Stark three months before he cracked.

He stumbled blindly into the kitchen that morning, his hair a mussed up mess and his eyes bleary from lack of sleep. He had obviously just come out of the lab from a three-day creating streak. Natasha sat on the kitchen island while Banner cooked breakfast. Clint had perched on top of the refrigerator knowing on a peppermint while Steve and Bucky were downing multiple bowls of cereal before enjoying their share of Bruce's eggs and bacon. Tony passed all of them up, grabbing the mostly cooled coffee pot and drinking straight out of it. Once he had downed a good six mugs worth he replaced the pot and stalked to the fridge. Pulling it open, Natasha was unsurprised to find it mostly empty despite Pepper having ordered in a delivery of groceries three days ago. Bucky and Steve had been up late last night and had obviously raided the kitchen in an attempt to emulate the piranhas they had watched on the Discovery Channel the day before.

The sound Stark made had everyone, even the two cereal piranhas, staring at him. Stark slowly slid to his knees in front of the open fridge, smacking his forehead against one of the empty shelves before making another impression of a dying pterodactyl.

"Why my doughnuts!?" He screeched. "Who ate my beautiful chocolate frosted doughnuts!?" Natasha glanced over at Bucky and Steve. They stared back at her before glancing at each other. It was Steve who finally spoke up.

"I think it was Bucky and I." He said quietly. Stark whipped around. All sorrow was gone from his face. Now, he was furious.

"Why do you guys eat so damn much!?" He yelled, his voice still one or two octaves too high. "Neither of you have gained so much as a pound in the past month despite the fact you've eaten everything but the flipping sponge! What is your secret!? Why are you eating all my food!?"

That was when it hit Natasha like a train wreck. Bucky and Steve had both been injected with super serum. The serums used were different, yes, but both increased strength, speed, and in effect their need for fuel. Records showed that Steve's metabolism was at least four times that of a normal human male. Bucky's honestly couldn't be far behind. They had to eat constantly in order to maintain functionality. Without constant fuel their bodies would begin to deteriorate in a desperate attempt to function, eating away at them quickly. Their blood sugar levels would fluctuate dangerously and it probably would only take a few days for them to become weak and no more than a week and a half to literally starve to death.

Deciding to share her newfound epiphany she slid across the island to stand between Stark and the resident Super Soldiers.

"You try living with a metabolism four times faster than normal." She quipped. So it came out more hostile than se had intended. In fact, a lot more hostile than it did in her head. But what was done was done and now she had to deal with Stark's reaction. To her relief, he looked shocked and even a bit apologetic.

"I-," He took a step back, shaking his head. "I'll have Pepper do some more shopping." He said quietly, directing his speech at the two serum-infused men.

That was the last they ever heard of it.

Steve and Bucky ate a lot of food. But the others knew, they needed the fuel. The fridge was always kept full, even after a night in by the two soldiers. And should someone want something kept safe for themselves, a sharpie marker was kept in the drawer by the fridge to mark things as private.

And no one touched Tony's chocolate frosted doughnuts.

A/N:

Because I just love the idea of Stark freaking out over having no food and it not being Thor's fault.