That's not fat it's magic power!
This side track idea that memorizing meat wizard spells makes meat wizards cranium bulge and their body look more ripped and muscular. Then i thought what if all spell casters looked fancy when "loaded" with spells?
Spells don't just need components they have side effects for storing them in your head. Some schools produce similar side effects. Some it is personal. Actually if you don't use for magic users would work for sorcery. Possibly this could all be side effect of some either magical ability. Work in Psychon better than my normal campaign possibly.
The more spells the more fancy and obvious the effects are. More spells total levels than your levels in spell caster means you look extreme and suspicious. Another possibility is they start after 5th level
d12 Spell Capacity Side effects
1 A glowing aurora forms with colour and shape indicating alignment
2 Body grows with bulging twitching muscles, veins and gristle
3 Cranium expands with throbbing twitching veins
4 Emaciation with body becoming more skeletal
5 Corpulent bloated jiggly body fat
6 Hair grows longer and animates (or beard, fingernails or eyebrows)
7 Begin to take appearance of a element
8 Decrepitude aging with terrible skin, hunchback
9 Youth reduce age increasingly to possibly child age or even baby
10 Body warps becoming hideous chaos freak
11 Plant features like leaves and flowers in your hair and green skin
12 Metallic, increasingly become stiff