Definitely true about science on it's own not being robust enough -- but I think you might be going a bit too far saying that "without a robust model of human m

Definitely true about science on it's own not being robust enough -- but I think you might be going a bit too far saying that "without a robust model of human metabolism/nutrition we just can't make claims like this". Yes, such a model would be awesome, but since it's not forthcoming any time soon, it is still useful in the meantime to be able to make claims of this nature using other evidence, such as experiments and even statistical studies, as long as we don't take results for 100% truth (although, taking model results for 100% truth would not be a good idea either).