It seems that Giant Pandas have gut bacteria that is not typical of a herbivore but more typical of a carnivore or an omnivore. I found this quite interesting 
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Panda Gut Bacteria Can?t Efficiently Digest Bamboo
BBC - Earth - Giant pandas' guts not suited to bamboo
.Panda Gut Bacteria Can?t Efficiently Digest Bamboo
BBC - Earth - Giant pandas' guts not suited to bamboo