It amazes me that so many people will eat lunch and two hours later blame the flatulence on what they ate for lunch.
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Gas by product of digesting the food would pass through quicker than the actual food I would think. At least that is how I remember reading it in school.
It has to do with peristalsis. When you eat something the whole digestive system kicks in. Whatever is in your large intestine starts moving and the gases associated with it are where the flatulence comes from.
On another note:
The conclusion: "Women had more sulphur gas and were judged to have more potent odour.''