“The Biggest Loser” caffeine feud just got piping hot — ’cause TMZ scored a peek at the show’s grocery list for contestants … and surprise, surprise, it’s stacked with caffeinated goodies!

Check the receipts from 2013 — the list, which we obtained from Jillian Michaels, straight-up name-drops Organic Dark Roast, Starbucks grounds, and a bunch of different teas. The shopping list of “approved foods” for contestants was attached to an email that a show line producer sent to the trainers and other staffers.

Obviously, several of those items totally undercut Dr. Robert Huizenga’s claim to us the show was 100% caffeine-free from day one … with coffee, diuretics, and weight-loss pills supposedly off-limits.

This is a big score for Jillian — who roasted the recent Netflix documentary, insisting caffeine was never banned and even waved around emails she claims back her up.

But Dr. Huizenga came firing back … saying Jillian was hustling her own supplements on the sly, claiming he shut that down himself, and said she even had to apologize on-air.