With his body probably. Knife seems like the kind of guy to admire a fine male form and be taken in by such.
Also, he seems like the guy who believes steadfast in Occam's razor, and eliminating what he thought was the problematic area of his previous terrible diet(carbs), being the myopic person he is, he latched onto PB eating all the meat and veg he could. Little does he know If Occam had any understanding of how extremely complex the universe actually is, he never would have posited such a failed technique of argument as the razor.
Tired eyes, like our tired lives