In laboratory experiments, a team at the University of Glasgow simulated what happens in the human stomach. They found vitamin C (ascorbic acid) mopped up potential cancer-causing compounds that are made when saliva and food mixes with stomach acid. But when they added fat to the mix, the ascorbic acid could no longer convert the hazardous compounds into safe ones.
Antioxidants like ascorbic acid protect against the formation of these nitrosocompounds by converting the nitrosating species into nitric oxide.
However, when fat is present, it reacts with the nitric oxide to reform nitrosating species, the scientists found.