but I will say that he is right that pound for pound there are many more calories in meat than there are in lettuce
It's too bad it's an extremely useless comparison, because
nobody eats lettuce for calories, even vegans. You might as well say that a hammer pounds nails better than a screwdriver.
In general, vegans have to either take supplements or eat a very specific diet to get the necessary amount of protein and calories out of what they eat (especially if they don't have any animal products, so no dairy, fish or eggs).
As far as I know, the only serious problem here is vitamin B12, which doesn't exist in plant sources (although it does exist in eggs and dairy), so vegans in particular need to take supplements, which isn't necessarily a big deal unless for some reason they aren't available at a decent price, which they should be.
Last I checked, Eskimos still exist, thus 100% meat diet works just fine.
It works, yes, but it requires a whole lot of care and some fairly broad practices; they pretty much let
none of the animal go to waste. As with any limited diet, just because you can do it doesn't mean it's remotely easy.
If there're any other people who conduct experiments on human as if they are animals so I can use as alternative, let me know.
I think it was more of a thought experiment than an actual proposition for a real medical experiment.
To reiterate, humans can eat a very wide variety of things, and crave a wide variety of things -- or at least
can. It all boils down to what we personally perceive as food, and what sort of diet works for the situation we're in.