Dr. Robert Huizenga isn’t about to let Jillian Michaels dominate the narrative — he’s firing back after she ripped him over Netflix’s “The Biggest Loser” documentary … telling TMZ her “receipts” don’t prove a thing.

Huizenga tells TMZ … caffeine, weight-loss pills and diuretics were strictly banned from day one — and anytime contestants claimed they were given such pills, he ordered production to shut down and launch an investigation.

He also points to the time Jillian had to give an on-air apology after being busted handing out pills to contestants to plug her own products — saying that alone proves her caffeine claims are running on fumes.

As we reported, Jillian went scorched earth on the Netflix doc “Fit for TV: The Reality of the Biggest Loser” — telling us it’s one giant lie, swearing caffeine was fair game on the show, and that Dr. Huizenga knew it … even posting emails she claims back her up, and declaring she’s gearing up to sue.