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Despite blasting "diet meals" in the Bowflex commercial, fitness model TJ Hoban tells TMZ -- he got his shredded abs nearly ENTIRELY by eating well ... not from using the Bowflex machine. Shocker.

According to TJ -- who proved his abs were 100% legit last night in Hollywood by lifting up his shirt -- the real secret behind a chiseled stomach isn't busting your ass on some trendy machine ... "It's all about diet man."

It's pretty crazy ... considering TJ squarely bashes diet plans in the Bowflex commercial -- claiming, "no diet plan" can build muscle and burn fat like the Bowflex machine.

We called Bowflex for comment -- no word back yet.