I remember some Wally stories talking about him having to eat a lot due to his metabolism, but it was before I was really regularly reading Flash and I don’t recall specifics.
It gets mentioned from time to time, usually to be played for laughs. I vaguely recall a scene in the old Flash TV series with Barry dumping a whole box of cereal in a salad bowl, drowning it in milk, and eating it at superspeed. The animated Justice League Wally takes his coffee with cream and 47 sugars (or something in that neighborhood).
None of them actually eat enough to support their speed metabolically, of course.
I remember a random Wally story from probably the 80s where ge lost his powers, and when they tried something to turn them back on, had a dozen or so large pizzas waiting for him to eat.
It was a running gag (no pun intended) in the short-lived live-action Flash TV series that Barry Allen began eating ridiculous quantities of food, including a scene where he’s gone through everything in his pantry and looks longingly at a large bag of kibble bought for his dog.
Damn, I loved that show (and so did my kids). Dealt with the problems of super-speed (first time Barry tried running, he was out of control and couldn’t stop), AND Mark Hamill did a manic job of playing The Trickster.
Although the TV Flash was Barry Allen, a lot of him was largely based on the post-Crisis Wally West, who was the Flash in the comics at the time. Wally started his Flash career severely powered down from Barry Allen levels and also had had the increased metabolism that kept him constantly eating.