In a recent reblog about super-heroes fitness, I put the tag "fantasy calories burning" before adding "I use this tag more often than you think".
And I realized... That's right. It is a recurring topic I don't see people talk about a lot but that I, as someone who likes to explore magic in fiction, stumbles upon from time to time.
When people talk about magic they love, absolutely LOVE the idea that "magic has a costs". It limits your magic system and your characters, it drives a story and shapes a narrative, it raises the stakes of the adventure and offers some nice motifs to weave... Everybody loves "magic comes with a cost". Sometimes it is just a generic "magic has a price" rule, a bit to which some works fully dedicate themselves (like xxxHolic, every wish comes with a price and not paying it is bad for the universe), and others rather brandish as a metaphor more than anything (Once Upon a Time, which both re-popularized and massively rejected after introducing it the sentence "Magic has a price").
Other times you have specific costs - like with what has become known as "Vancian magic" where, in its strictest sense, spells occupy literal brain-space. Taken out of "The Dying Earth" into "Dungeons & Dragons" it became a well-known trope, with variations found everywhere (Discworld, Young Wizards, DIE, Invisible Sun, the Second Chronicles of Amber...).
But then you have magic being... caloric. This is a take on power that is usually much more present and used in sci-fi settings: specifically super-heroes tales. The two main variations I could identify of "caloric magic" both are very prominent and most examplified by super-hero series. Case A: power requires the consumption of a larger amount of calory than normal, well that's the Flash, or Hulk, or Wolverine/Deadpool. Case B: power relies on the body fat, its burning and its repletion. Well, that's Fat Gum from My Hero Academia. [Though, to be fair, Fat Gum's character as a cartoony fat guy turning into a handsome beauty through extreme and rapid weight loss in times of tension... This is part of a wider trope in animes and mangas found everywhere. Rikio of "K-Project", Isami of "Food Wars", Inada of "Silver Spoon", Honda of "Shirobako"... Japanese creators love the dichotomy of a same person switching between cartoonish obesity and fashion-model-slimness. It's a thing.]
But it exists beyond the super-hero genre and can be used in fantasy. Rarely, mind you, it is mostly found as obscure details in more famous works or in little works of "second-rank" in the wider scope of fantasy publications. The most famous case would be the famous (or infamous depending on what you think of it) series by Robin Hobb "The Soldier Son" where magic is literaly at - accumulates as body fat within the body when the wizard doesn't use it, and then causes massive weight loss when spells are cast. Wizards forcefully fattening themselves up because magic causes rapid, intense, potentially-lethal weight loss is found in works such as Garland's "Demon Blade" duology or Scott Lynch's potential series of The Red Hats (if he ever continues his "Effigy Engine" series). The Wheel of Time rather used the case A for its healing magic, showing that for great healing spells a large consumption of calories is required - though this is part of another recurring idea I was not actually aware of until I found the website TV Trope gave it a page, the idea that "healing magic" is a very difficult and complex one... Which allows me to jump on "Delicious in Dungeons", which also quite famously uses this caloric magic/weight loss as sign of magic for its healing and resurrection spells.
[I also heard that the first novel of the Spellsong series, "The Soprano Sorceress", uses this motif? But I did not read this series. I suspect, given it is entirely about the world of singing, that it is a reference to the heftiness and largness of opera singers? Back then it was common enough for people to draw upon it.]
The case A of caloric magic, caloric-consumption because of huge energies being drawn, is more widely accepted than case B, because it relies on actual fitness and sportive and anatomical logic that we are more accustomed to and science-fiction helped spread in popular works. Case B, magic manifesting as fatness/stored in fat, is less known and thought as weirder, yet it is not as weird, when you think about it, as "magic uses age". The cost of magic being youth, or life-time/life-force, and resulting in people growing older the more magic they use, is a VERY famous fantasy trope today.
From "The Golden Voyage of Sinbad" to "Stardust", passing by various adaptations of Snow-White or old folktales, like this one claim that Baba Yaga ages with every question she answers. (I also heard this trope was used in the Iron Tower series/Silver Call duology? But that's an alternative-Tolkien-pseudo-sequel I have not read yet...). And somehow, the case B of caloric magic relies on this same concept as "the consumption of life-force to power magic", "the sacrifice of the self at the risk of death", which is itself such a common concept in magic-writing that we tend to forget about it (a most famous case would be Belgarath's mid-series breakdown in the Belgariad, where it is explicitely said that sorcerers can sometimes reach too much within themselves when using magic and exhaust themselves beyond safety when practicing spells - at best, resulting in them losing their powers, at worst killing themselves).
And it is not as if the idea of "magical fattening" was not from our world too... Though it exists rather as a "ritualistic fattening". The same way Le Guin was taking inspiration from various non-European magical and religious practices to build her magic system in "Earthsea", Robin Hobb's creation of the Great Ones, the obese-sorcerers fattened up to gather magical energy, themselves take inspiration from non-European social practices. Most of the time these traditions are covered up by sensationalistic media and they are focused about fattening up for marriages. Many countries have the habit of fattening up their men or women to make them more desirable and likely to get a profitable wedding - the leblough tradition of Mauritania, the "biggest man" competition of the Bodi in Ethiopia, the fattening rooms of Nigeria... But sometimes the force-feeding is not just for social status or erotic purposes, and becomes more symbolic and occult, usually as an invocation of prosperity to counter an upcoming famine: such are the double-use of the Guru Walla of the Massa in Cameroon, or the Polynesian "ha'apori" ritual in Pacific areas.
Why am I digressing about all this? Because I want to talk about the way "Names = power" has been taken wildly out of context and reinterpreted in a very strange way... Going from non-European traditions to being perceived as a core part of European legends when it was absolutely not. But that will be for a next post about magic.
[And of course, being a Discworld fan I have to point out that, sometimes in fantasy, wizards are all fat without any link to their use of magic. The Unseen University is a proud example of this.]