Honestly? Because I imagine being in the limelight growing up, he’s incredibly aware of what he looks like and what he must eat to stay fit. People are shitty to celebrities if they even have an off-day where they don’t wear makeup while getting a coffee from Starbucks. That’s got repercussions. I imagine Tony remembers his freshman fifteen not as “oof, everyone gained so much weight that first year away from home,” but as “Magazines had pictures of me on their front covers speculating about my appearance, health, studies, and rated my sexiness when I was fifteen years old.”
I also imagine that if Tony doesn’t have a full-blown eating disorder, he definitely has disordered eating, constantly calculating his calories-consumed vs calories-burned and what his macros are and how much he has to exercise because of it. His coffee addiction isn’t so much for the caffeine as it is to keep him full so he doesn’t have to eat as much. He’s not shaking because he’s had nothing but coffee for three hours; he’s shaking because he’s had nothing to eat in six and the last thing he’d eaten was a banana slathered in peanut butter.
The only reason he ever gets control of it is because of Afghanistan. He and Yinsen share meager rations of food, sometimes only a handful of rice a day, and he’s always felt a little hungry but this is somehow worse, because he’s not in control and he wants to survive. He does. Then one day they’re given a handful of grapes, and he nearly weeps because it’s new and different and sweet. He’d never let himself indulge in fruit much other than as dessert because of all the sugar in them before. Now he wants nothing else.
“I want… oranges,” Tony says in the helicopter after Rhodey finds him.
“Okay,” Rhodey says, and buys all the oranges and pears he can find while Tony’s seeing the doctor, and doesn’t say anything when Tony tears into the oranges like a starving animal before going for the pears, because they, at least, don’t need to be peeled.
(“I want a cheeseburger,” Tony says in the limo.
Happy’s eyes dart up to the rear view mirror to look at him in surprise. Tony typically didn’t just randomly indulge a burger without some serious calorie calculations. But Tony is skin and bones, so he just nods, and says, “Sure, Boss,” and finds the nearest burger place.
Tony eats two burgers and a chocolate milkshake before he even touches his mountain of fries and doesn’t immediately start mumbling about macros and cardio and cheat days after he finishes.)
((Pepper finds bags of snacks all over the place. They’re small things, things that will keep–a bag of dried mangoes, a kids’ pouch of applesauce, a packet of beef jerky. The coffee pot is only half-empty. There’s a blender now.
“Smoothie?” Tony asks.
Tony had avoided juice and smoothies like the plague, before.
“Sure,” Pepper says, and watches Tony coach Dum-E through making a smoothie.))
(((Obie buys pizza, which has always been his special treat for Tony. Tony gobbles down three pieces before he can even finish one, when before he’d have two pieces and save the rest.
“Maybe you should slow down,” he suggests.
Tony’s hand hovers over the box before he draws it back into his lap.
It’s only later, after everything is said and done, that Tony notices his real friends said nothing about him eating more; Obadiah had been the only one unhappy about it.)))