I looked into this diet as well once. I opted for a 21 day diet challenge instead. No animal products, no grains, no beans, no fun... I did eat potatoes.
Are you allowed on this diet to fry potatoes?
Anyway, good luck my friend, I myself lost about 20 -25 lbs in 21 days, I can't remember the exact amount.
I mean, there are no hard and fast rules, but to do it the way it is described in Penn's book is to not fry them. No use of oils, butter, salt, lard, any of the nasty stuff.
I have seen videos of people who fried them (French fries and or hash browns) and then complained because they ate all these potatoes and didn't lose any weight, so I am sticking to the basics. Boiled, baked and microbaked, mashed or twice baked. With a little pepper and adobo for now, although apparently there are some varieties of Mrs. Dash that are good without the added salt that Adobo has, so I will likely be trying those.
There is salt free Mrs dash, I use it and it's OK. Here's my salt free adobo like powder...
All equal parts. Onion powder, garlic powder, dried and powdered oregano (I use a coffee grinder) cumin, paprika (I like smoked paprika), and some kind of Chile pepper powder, Korean red Chile pepper is awesome.