Question: How soon after eating do people begin farting?
Short answer: 11 minutes.
Long answer: It is well known that people fart more after a meal. One obvious reason is that the digestion of food creates the gaseous products of farts, but this reason does not account for the time between eating and farting. For food to pass from the mouth through the stomach and intestines usually takes at least six hours, but many informal observations suggest that farting begins much more quickly after a meal.
This rapid onset of farting is almost certainly due to the gastrocolic reflex. This is a physiological reflex that increases the motility of the colon in response to the stretching of the stomach that occurs with the ingestion of food. An overactive gastrocolic reflex is associated with various gastrointestinal complaints, such as stomach pain and cramps.
Myoelectric recordings from the colon have shown that there is an increase in muscle activity almost immediately after eating, creating pressure to release the contents of the digestive tract. This increase in activity can be seen within the first 20 minutes after a meal (Snape et al., 1979):
These data predict that farting should occur no later than 20 minutes after a meal. To test this hypothesis, we recently attended a large social gathering that was hosted in a banquet hall near the College. The gathering was attended by roughly 300 people. We positioned an air quality sensory within the banquet hall and gathered data during different phases of the event. The resulting data are shown here:
We see two distinct phases of farting, both locked to the appearance of food. The first begins 11 minutes after the service of hors d’oeuvres. It persists for the duration of the food service (blue) and for some time afterwards.
The second phase of farting follows 10 – 12 minutes after the main meal service (yellow) and continued throughout the duration of the event. Levels of VOC seemed to asymptote at around 1.5 ppm, indicating that a significant amount of fart smell was being continuously released into the banquet hall.
These data indicate that, at least for large gatherings of people, farting begins very quickly after food is served and potentially continues for a very long time afterwards. In our data, farts were detected even more quickly than the intestinal motility results would have suggested. The precise dynamics of fart release can probably be captured by our leaky integrator model of farts, and this will be the topic of a future post.