Could it be a continuation of accidental magic that continues to affect them throughout their lives? Maybe it protects them from blunt trauma that would kill an ordinary person but magic itself is immune to the protection, explaining why they still get hurt from a Stupefy.

 

Rowling:

So yeah.

 

It was retconned about four years before Pottermore. As best as I can tell, Rowling didn't really think through a lot of the series that far back so anything she said was just a guess of an off the cuff response until she got towards the end of the series and abruptly realized that she needed semi-coherent backstories for people.

 

Maybe some wizards age slower, some are resistant to common maladies and others to external threats. It could be that it depends on how the person develops his magical talent.

 

Is it common for wizards to live well past 100? Or are Dumbledore and Dippet an exception to the rule?

We know Dumbledore had access to the Philosophers Stone for a portion of time maybe that is why he ages better than muggles.

As for the obesity issue, you'd be really suprised if the wizarding world didn't have some sort of fix for that given what can be done with transfiguration and healing.

 

So you are basically saying that Slughorn WANTS to be fat? Or that he eats so much that even magic doesn't stand a chance?

 

Wizarding culture might just not give a shit if someone's fat.

 

Unlikely, as ideals of beauty seem to be roughly the same, given how Fleur is described.

 

Maybe Slughorn's fatness is due his liking for fancy magical food that causes supernaturally resilient obesity.

 

It has to be the potion fumes

 

Weightloss spells could be less effective on certain people? At the end of the day, in the muggle world you could argue that most people have the ability to control their weight and yet obesity still remains an issue.

I guess it's far more likely that Hogwarts students are relatively in shape is because they have fairly active lifestyles for teenagers. Most lessons are more practical, even Herbology is likely to burn more calories than a muggle science lesson. The castle is large and walking is the only way to get around it, stairs are also a effective form of excercise. Install some lifts and Hogwarts would get it's fair share of fatties.

 

Whenever Hogwarts senses that a student is starting to get overweight the staircases, instead of moving randomly, will turn into reverse escalators in order to force them to exercise.

 

I don't think you can argue that, because in the muggle world there is the issue that it's actually hard to lose weight. Wouldn't be the case for wizards, if a spell/potion existed that made it go away without any effort.

However, I don't believe that. First of all, permanent changes to your physical appearance don't seem possible through usual magical means, given what we know from canon (I could be forgetting something, please tell me if I am). Height-enhancing potions, Puberty-speeding potions, permanent glamours - don't seem to exist, neither does a weight-reducing potion, because otherwise, Slughorn presumably wouldn't be fat.
Yes, you can explain that away. But since we can only guess, I think we should cling to what few hints we have - and not try to invent exceptional circumstances that say differently.

 

Well, Hermione fixed her naturally abnormally-large teeth with a shrinking charm at one point, so there's that. Permanent magical alterations to your appearance are definitely possible, but that's the biggest one we ever see canonically.

Honestly, if I had to go with a Head Canon on things like magical weight loss, my off-the-cuff response would be that it's pretty much the same as it is for us muggles; yes, there actually are simple, easy and effective weight loss solutions, but they aren't safe so their use is restricted to the most extreme possible cases and even then people are hesitant to use them. For Wizards, these would be a Weight Loss Potion which comes with some very risky side effects and can kill you. For us, they're Meth and things closely related to it.

 

Regarding weight loss and obesity, if you're of the belief that witches and wizards do have a greater resistance to trauma and maladies then it follows that you don't get very many obese magical people. Obesity causes a lot of mundane problems, just like OA, cataracts etc. etc. Harry would never think to ask, but it doesn't seem like elderly wizards seem much bothered by shit like that. I lean towards it being a mixture of both their innate nature and magical remedies though, and you could tweak it towards one end or the other of the spectrum depending on the specific problem.

With trauma, I'm definitely inclined to believe that it's in large part due to their inherent magic. They have a lot of defensive spells they can cast, and they can apparate etc. But, when a witch or wizard takes the hit, I'm inclined to believe they can tolerate it better.

Quidditch has been discussed but I haven't seen anyone mention spliniching. Apologies if I missed it. Reading the earlier books, splinching is described almost comically. People being in two places at once, body systems completely disrupted but still alive. It seems like a harmless but frustrating issue due to a lack of skill or trying to do something without being taught, like stalling a car. The later books make it a lot more frightening, it's very much like 'driving' for wizards and splinching are the car crashes. The fact that wizards can survive some of these accidents for long enough for help to reach them definitely makes me think that they can innately resist more trauma.

 

It's all based on the notion that the Hogwarts population is lacking its fair share of fat kids.. which i guess is just because the main characters aren't depicted as being overweight (exclude Slughorn, Vernon D and Dudley D).

Unless there has been something released on Pottermore that states that all the Hogwarts students are skinny, I don't think we can argue that Hogwarts definately has a lower percentage of obese children than a regular muggle school.

 

There are others that have been described as large besides Slughorn. In the illustrated CoS book, Molly Weasley had a bit of heft to her. Crabbe and Goyle were described as large even at age 11, far too young for that to be muscle. Plus there's Umbridge, who's described as toad-like, as in wide. I'd always pictured Fudge as being comfortably overweight.

We really only get to see a rather small percentage of the wizarding population, and character descriptions are usually very short. Unless it is important to their character's image like Slughorn, their weight is usually not mentioned at all. So really there's too little information to draw the conclusion that wizards are resistant to weight gain.

 

When I was a kid I always thought of Neville as fairly pudgy, though I don't remember if he was actually described as such in the book. The movie didn't go with that in any case, obviously.

 

I think there's a solid line of thinking towards some innate magical protection. Subconscious magical resistance, perhaps it could marginally slow an approaching danger (like a bludger or Neville's fall towards the ground). Combine that with decreased healing time, magical resistance to illness, and then of course spells and potions to heal - and that can certainly contribute to a longer life expectancy.

 

A bit late but i want to add that it is revealed that in the new movie fantastic beast that wizard and witch do have a better durability and constitution than muggle seeing how newt give kowalski helm and body armor when dealing with his escaped beast saying how his muggle body is weaker than wizard and witch.