I, too, love the potato. I like to boil them with broth, oil, lemon juice, and garlic and spices, then lightly roast to finish.

> I read once that humans can live on a diet of potatoes and milk

Protein is not a monolith; it's nine different compounds that are needed, for humans. Meat has all of them. But most plant foods do not. A person will eventually starve from lysine deficiency if they eat nothing but wheat, rice, millet, most grains really. Even though these are rich in protein. That might be why bread and rice is so often paired with beans; beans are rich in lysine and the combination covers all the bases.

One of the proteins that the potato lacks relatively is methionine; a large active adult man needs perhaps 1 - 2 gram of methionine per day. Potatoes have about 500 mg methionine per kg. That works out to some 2 - 4 kg of potatoes a day and some 1500 - 3000 calories to go with it. (Plausible enough, if you ask me. When I was younger and worked a labour job burning lots of energy I would cook a 2 kg bag of potatoes and they'd be gone in a couple days.) It does seem nothing but boiled potatoes, salt and maybe a multi-vitamin and some fat, will keep a person going more or less indefinitely. I can't do the mostly-potato diet myself anymore though. I would get very fat.