Cancer is Curable NOW
Forks Over Knives
Fat, Sick, and Nearly Dead
The Gerson Miracle
The Beautiful Truth
Dying to Have Known
I have seen a few, but not all of these (and I've seen some you didn't list). Most of the food/health/nutrition documentaries that I have seen had some really good information, but also some pretty questionable information. They also can use some pretty questionable tactics to impart that information.
That said, I do think there are many people who will see some of these movies who will never sit down and read a book. So, I think it can be a great way to get information to new audiences. However, I also think the movies can send the wrong message.
Case in point: Fat Head. Fat Head does a really good job of explaining in layman's terms the basic problems with the lipid hypothesis. But, the whole movie is centered around a guy promoting McDonalds as health food as long as you skip the bun (sometimes) and the fries (always). Nothing could be further from the truth. He backpedals a bit at the end of the movie, but IMO it's too little, too late. There is also a big disconnect between what he and the experts are saying (fat is fine, but refined carbs are not) and what you see him doing in the movie (eating burgers with the bun and holding a meal tray with fries on it). My concern is that people who are not particularly knowledgeable about nutrition will see that movie and take away only the "fat is good" message without understanding that loading up on fat will be a disaster if you continue to eat mountains of refined carbs like sugar and flour with that fat. And, not only that, the fat which is good is not the same fat you are getting at McDonalds.
Of all the food/nutrition/health documentaries I've seen, I'd have to say Food, Inc. was by far the best. King Corn (which you didn't list) wasn't bad, either--although it had some really slow parts.
There are bits of truth sprinkled throughout these. In the case of cancer I'm sure that there are some alternative methods that work. For example there is one guy Simoncini who claims to be able to treat cancer with Sodium Bicarbonate. I think that there is some merit to his claims however I don't think it's the end of the story. At first I was pretty skeptical but then I went and looked up that some types of chemotherapy are more effective when delivered with sodium bicarbonate. It got me to thinking wouldn't it be funny if the sodium bicarbonate was actually the "enabling" ingredient in that concoction.
My grandmother died of cancer. Simultaneously my while my mother was taking care of her she was diagnosed with breast cancer. Both were treated with conventional treatments. My grandmother died and my mother is still alive 15 years later. My mother received chemotherapy delivered alongside sodium bicarbonate. I remember going to the doctor's office with my mom to watch the doctor give her chemo when I was a kid. I remember asking what all he was doing, as if I somehow I was overseeing the procedure, lol, first a sodium bicarbonate injection then the chemo injection.
Anyway, there are few documentaries that present only evidence, a lot of these pick evidence that support the message they are trying to get across. It's likely that the useful answers are not laying on the outside edges of the extremes. I think it's important to look at a variety of sources and let your brain and your own experiences decide what is applicable to you.