He's a human optimization expert, totally legitimate, and not a snakeoil salesman, who just so happened to put on 34 lbs of muscle IN A MONTH following a style of training, HIT (not to be confused with HIIT cardio), that the scientific literature has largely debunked, that was used as a marketing ploy to sell exercise machines and ultimately a company (Nautilus), and has historically only been used and promoted by a small minority of bodybuilders, the most famous of whom (Mentzer & Yates) may not have even used it, and were voracious users of PEDs even by professional bodybuilder standards (Mentzer used meth before workouts, and died at 49 of a heart attack). As Tim describes (can't link to it without getting caught in the spam filter):

> I weighed 152 lbs. for four years of high school, and after training in tango in Buenos Aires in 2005, that had withered to 146 lbs. Upon returning to the US, I performed an exhaustive analysis of muscular hypertrophy (growth) research and exercise protocols, ignoring what was popular to examine the hard science. The end result? I gained 34 lbs. of muscle, while losing 3 lbs. of fat, in 28 days.

He's written a series of human optimization guides, including the 4-Hour Body: An Uncommon Guide to Rapid Fat-Loss, Incredible Sex, and Becoming Superhuman. Totally legit.