Take that documentary with a grain of salt. While there is certainly a lot to recommend removing junk food & processed foods from your diet, and eating nutritious real foods, whether you have cancer or not, the Gerson diet has never been proven to be superior to other forms of cancer treatment -- the Gerson Institute refuses to release statistics, from what I've read. Various sources suggest that carbohydrates allow cancer to survive and grow, which would recommend against taking megadoses of veggie & fruit juice, as the Gerson therapy requires. In summary, for cancer treatment, I've never come across any evidence that the vegan Gerson therapy is any better than a VLC, paleo/primal regimen would be, and according to certain sources, the excessive carbs & lack of protein in the Gerson therapy would actually be drawbacks.

When my dad was diagnosed with stage 4 prostate cancer, he joined an experimental trial in Canada. I can't remember the name of the drug tested, but he was advised to eat no more than 10% fat. He was also diabetic, so he was already avoiding sugar and I made him apple pies with (swallow) granulated fructose.

He'd been told by his US doctor he had less than 2 years and with the above protocol he lived 4 healthy ones and a final year of gradual deterioration. (He loved the apple pies.)

Oh, regarding the protein question I fed him plenty of meat but I did watch fat very carefully. I also fed him whole grain breads and other carbs. Lots of fruit and salads too.

That doesn't say anything for or against our ancestral health principles, it's just what happened at the time.