"Chlorophyll will only make oxygen in the presence of light. It’s dark in your intestines, and even…"

““Chlorophyll will only make oxygen in the presence of light. It’s dark in your intestines, and even if you stuck a searchlight up your bum to prove a point, you probably wouldn’t absorb much oxygen in there, because you don’t have gills in your gut. In fact, neither do fish.””

Dr Ben Goldacre on BadScience.net