Echoing Echo, here.
I am a scientist, one who studies human genome variation. I haven't watched this movie but in general the science behind any "one true way" diet perspective is incomplete because there's a lot we don't know about metabolism. That doesn't mean it's bad science, but what works for one of us might not work for the other.
For instance, lactose digestion is one of our best examples of measurable human evolution. Everyone makes the lactase enzyme as a baby to digest mom's milk. Originally, humans stopped making lactase as they got older. That means when you drank milk it would get digested by your gut bacteria and give you gas and other ickiness. But a chance mutation in a European tens of thousands of years ago made the lactase enzyme stick around through adulthood. That variation turned out to be useful to Europeans, because milk from domesticated animals became a good food source, so it won out over the original version and now 80% of Europeans have that adult milk-digesting version.
That doesn't mean at all that it's the only thing that determines whether milk sits well with you. Gut bacteria are still important. And there may be other reasons why milk is problematic - plus, in my opinion, the antibiotics and hormones used in large-scale farming cause problems too. But anyway, as far as science goes, this is the textbook example of differences among different human populations.
Another real genetic variation: Like many many Irish people, I carry one copy of a gene variant that causes hemochromatosis if you have two copies. That's a disease where your body absorbs iron like crazy. So, instead of worrying about anemia from not eating enough red meat, people with hemochromatosis have to avoid iron and donate blood often to avoid organ damage from too much iron. I just have one copy of it, so it's not a disease - but I bet the large percent of northern Europeans who have this variation like me need less dietary iron than average. It might explain why I have never ever been drawn towards eating red meat even when I'm very athletic. Who knows.
And these are just the slam-dunk examples of genetic variation and diet. There are thousands of tiny differences that have effects we're only starting to understand. Even if we never understand it, though, I'm personally happy with the Michael Pollan guidelines: Eat real food. Not too much. Mostly plants.
