@Invisifat  
Maybe Pinkie has a reinforced skull like a woodpecker does in real life, that protects it from ‘rattling’.

The irony is, the constant jumping probably does help her burn that energy, and the “rattling brain” problem isn’t a thing as her conversations with Spike have proven.

@GaruuSpike  
Have we ever seen her eat anything beyond pastries? That is kind of her thing.  
Also, don’t take this show so seriously. It is a cartoon, and therefore it doesn’t have to follow the same rules of physics as real horses or humans do. After all, this is a world where magic, dragons, griffins, and hippogriffs exist, where ponies can sleep on clouds and where entire castles can grow out of the ground like a tree. So knowing that, is it really illogical for Pinkie to only eat cake and look as healthy as every other pony? Honestly, I think not.

@WyrmSpawN  
It’s a myth in the sense that most people don’t understand what it is. It’s not some magical entity that controls whether you get fat or not, and it’s not something that is “set” at birth that is completely out of your control. It can be raised, a lot, by good exercise habits, or even just moving around a lot.
 
Pinkie does both. The constant jumping is both intense cardio and intense strength training. On a daily basis. All day, every day. You can’t out-exercise a bad diet, but you can out-exercise a mediocre one. If Pinkie eats plenty of actual food instead of just candy and pastries and soda, then she can avoid chubbing out, but she’ll never be cut like a marble statue unless she stops with all the sugar.

@Scp-3125  
Eh, true. I don’t think anyone would want that

At least you don’t have brain damage induced by years of constant micro-concussions

@Enmity1498  
Ponies in the show appear to be ‘lacto-ovo vegetarian’ - they keep cows & chickens, eat cakes, cheese, etc.
 
Horses are herbivorous, but most likely also consume quite a few insects as they munch their way across a field. Sometimes these weird monkey-things will feed them meat and fish too. Ick. >.<;

@Background Pony #1EC7  
Good point. I know that real-life horses have very different metabolism compared to humans, so I would guess that the difference in metabolism would carry over to ponies in Equestria, as well (and as you said, all food there is vegan due to horses not being able to eat meat. So that definitely helps a lot)

@Olpert  
Honestly, after reading several pages of this comic, I can see what you mean by that. It is like they took the characters of MLP:FiM and put them into the world of Seinfeld

@Enmity1498  
Because this writer has abandoned all concepts and characters of the show and just wants to do an 80s sitcom.

@Enmity1498  
They are also ponies. Very few of them are “fat” because they don’t have a human metabolism that stores excess energy as fat. Also, they seem to have vegan alternatives to fast food there, which helps.

@Background Pony #1EC7  
Why is this even an issue? Twilight has never looked out of shape, and neither have any of the other Mane Six ponies. I assume that they all get plenty of exercise, or eat the kind of foods that fits with their daily routines. Pinkie burns more calories on average than all other ponies save for AppleJack and Rainbow Dash, so she eats more. I would say it is similar to Barry Allen in DC

But moving around and jumping does make you burn calories instead of, say, reading or sewing.  
People won’t understand the miracles of peripheral or unconscious exercise on your metabolism.

I love that last panel!
 

I miss my good metabolism…

The real explanation here:
 
Cocaine is a hell of a drug.

I have a friend like that. I eat salads and carefully count calories for months and lose 4 lbs. He eats pizza, ice cream, burgers, king size candy bars, sits around playing WOW all day. Not even 110 soaking wet.

Hopefully this doesn’t mean that they start rejecting Pinkie again for her personality
 
It gave me the impression that the author does not like Pinkie very much and gave the role of pinkie to Lyra as the pony that likes to see others happy

https://www.youtube.com/watch?v=xOUTimHYj5w
 
@Digi [FiM]  
A myth? No. Overemphasized? Perhaps. Food intake and physical activity have more effect on body mass than naturally occouring variations in resting metabolic rate.

Why is Poop on the menu at Sugar Cube Corner?

You know how she has said great metabolism? because shes ALWAYS active.

@WyrmSpawN  
Sort of. Mostly, its used as an excuse by overweight people i.e. “I don’t have a good metabolism like you.”

I hear ‘good metabolism’ so much I’m starting to think it’s a myth.

Eh, I think that Pinkie might have a Kirby-like universe in her stomach, giving her the ability to eat as much pie as she wants