Control. That's what it started out as. It was just a way to feel a sense of something when life got hectic. Trying to balance schoolwork and "Spider-manning" had become increasingly difficult, and life had begun to feel chaotic. He was constantly worried about letting May and Tony down by not keeping his grades up, or letting the people of Queens down by not saving as many people as possible. It was just a way to cope with the stress. Peter had never meant for it to become something that controlled him.
It started out small. Just leaving a few bites on his plate after meals, or eating the amount a normal person without an enhanced metabolism would have to eat. Before he knew it, he began cutting out "bad foods" like soda, chips and candy. Pretty soon, Peter began limiting his carb and fat intake, telling himself it was healthier anyway, and before he knew it, his meals consisted of nothing but steamed lean meats and vegetables.
Before he knew it, his weight began to drop rapidly. While Peter had never had body image issues in the past and was well aware that he was nowhere near fat, he couldn't help but feel proud when he began to notice that his nerdy science t-shirts were starting to hang off of his smaller frame, or that his jeans were starting to sag as his waistline began to shrink. Schoolwork had become increasingly difficult to keep up with as he began spending more time going out as Spider-Man and less time sleeping. As his grades began to slip from A's to B's, it felt good to accomplish something, even if that something was dropping weight that would damage his health.
Peter began weighing himself. He felt pride every time he lost a pound and shame every time the scale went up a pound or stayed the same. The numbers became an obsession, and they began occupying his every thought.
The obsession with numbers turned into counting calories. At first, the number started out at around 9,000 calories, the amount Peter calculated that he needed to maintain his weight with his enhanced metabolism. The number soon decreased to 2,500 calories a day, after all, that was the recommended amount for the average adult male. Pretty soon, Peter got rid of his calorie goal all together and decided to eat as little as possible, and tracked the few calories that he did eat when the hunger became unbearable.
By the time anyone caught on to what was going on, Peter was already deep into his destructive habits. Of course, he had a hand in hiding the problem via clothes and small lies he would tell Tony, May, Ned and MJ, like "I ate while I was out on patrol", or "I feel a bit nauseous right now, I'll eat later". Later never came.
—
"Hey Mr Criminal, don't you know that it's rude to threaten an old lady with a gun?" Peter taunted a mugger one night out on patrol.
The mugger Peter was attempting to take down should've just been another run of the mill criminal. On any other day, Peter's Spidey sense would've warned him that if a criminal was about to turn a gun in his direction, and would've webbed up the weapon and the criminal before they even had a chance to shoot. However, with Peter only eating a small fraction of what his body needed, his powers were acting up. While he was able to narrowly dodge the bullet with an impressive backflip, and stall long enough for the old lady to run away, he was unable to web up the criminal in time and the mugger ran off.
"Karen, where'd he-" Peter was unable to finish his sentence as the edges of his vision began to darken. He was falling face forward onto the concrete as he lost consciousness.
—
"NO YOU CAN'T CRYYYYYY PRETTTTTYYYYY YEAH…" Tony belted as he worked on updating the Iron Spider suit. After the whole "Infinity War" debacle with Thanos, Peter's suit had taken quite the beating and Tony was determined to make it invincible as he could not bear the pain of losing Peter again. As for why he was blasting a Carrie Underwood song in his lab, let's just say that Tony had a guilty pleasure of listening to the amazing artistry that was country pop. After Peter had introduced him to "You Belong With Me" by Taylor Swift, he couldn't get enough of the stuff (not that he would admit it to any of the Avengers, they would never let him live it down).
"EMERGENCY ALERT: BABY MONITER PROTOCOL" Friday interrupted Tony mid-way through his rather impressive vocals. Tony immediately dropped the screwdriver he was holding and activated his nano-tech suit.
"What's going on Fri, is Peter okay? Show me his vitals right now," Tony frantically yelled as he began flying towards Peter's current location.
"It appears that Peter is currently unconscious as a result of low blood sugar. According to Karen, it seems as if Peter has not eaten since yesterday morning."
"What, why would Peter go out patrolling without eating? How has he not eaten since yesterday? I know that kid has no sense of self-preservation, but with his enhanced metabolism, he shouldn't go two hours without food!" Tony exclaimed in terror. Tony had already lost the kid once when he turned to ash in his arms, his damaged heart wouldn't survive if he lost Peter again.
"Karen has informed me that Peter has been keeping detailed logs of his calorie intake in his suit logs. His average daily intake is around 500 calories a day. Peter has also kept detailed logs of his weight. According to his charts, he has lost over 30 pounds in the past month. His body is showing signs of starvation not unlike an individual suffering from Anorexia Nervosa," Friday replied, a hint of concern seeping into the AI's voice.
Tony would have fallen out the sky had he been in charge of piloting the suit and not Friday. A stream of old memories of a fourteen year old with a feeding tube began to cloud his vision. The numbers, the rituals, the screams from Howard Stark to get his "goddamn shit together" and to stop "being a sissy". God, how could I have missed this?