I suspect well over 50% meat in their diet, maybe upwards of 90%. Look at the abdominal muscles and shape compared to a gorilla. Gorillas' large gut is needed to process enough plant material to extract the necessary nutrients and calories. (This would also be why the trail of plant destruction Norseman hypothesizes is necessary is not found ... because they're not eating plants in similar proportions.) It does not seem to be present in sasquatch based on the reports, instead, they look pretty much like us but bigger. Most of that "bigger" seems to be muscle, not digestive equipment. So, going out on a limb perhaps, I think most of their dietary calories, etc come from meat, and plants are used only to provide specific "stuff" not available, or slightly deficient, in a meat diet.
I guess we're going to have to wait to find out.
MIB