100 pounds in about four months. And five years later he apparently has kept virtually all of it off.
The first two weeks are nothing but potatoes. Boiled or baked but not fried. With nothing added: no salt, no butter, no anything. Mandatory to also eat the skin.
Details are in Penn's recent book, Presto! How I Made Over 100 Pounds Magically Disappear and Other Magical Tales. I read it and I think it desperately needs a good editor. Interesting but it would have been better at half the length.
His diet guru is Ray Cronise. One piece on his thinking is here: "Ray Cronise Wants To Fix Our Broken Plate".