Most of us open our bowels once a day on average but in reality normal bowel habit constitutes a range - from every third day through to three times a day. Anything outside this range suggests an abnormality in the bowel itself. The bowel is divided into the upstream portion known as the small bowel and this is where all the goodness is taken out of food into the body. The lower half is known as the large bowel and consists of the colon and rectum.
Under normal circumstances, by the time the gut contents have reached the last part of the small bowel it is all waste (faeces) and quite liquid. The function of the colon is to extract water from the faeces - all the while being pushed toward the rectum by muscular contractions of the bowel wall. Normal colon transit time is 12- 24 hours - the faeces thickens up as more water is drawn out so by the time it gets to the rectum it is the consistency that we recognise it as. Faeces is coming through the colon fairly constantly and to save us going to the toilet constantly it is stored in the rectum. Once the latter is full we get the urge to defaecate and off we go.
Within the normal range, as stated above, our bowel habit is largely dictated by what we eat. However, even on the occasions when we briefly starve ourselves the bowel will still work due to the fluids produced by organs such as the pancreas and the liver and because the bowel wall is constantly shedding dead cells from its lining. Fibre is an important element in our diet as it adds bulk to the faeces and gives the colon 'something to work on', so it tends to make you more regular. We derive a lot of our fibre from fruit and vegetables - hence the reason why we stress the importance of these in our diets.
Flatus, or wind, is a feature of a healthy colon and is a by-product of the harmless bacteria that reside in our colon. What some people view as excessive flatus is in fact an indication that we are eating the right foods as it tends to increase with the amount of fibre that we take in.
If your bowel habit is less frequent than every third day then this suggests either slow transit constipation (a failure of the nerve supply of the colon) or obstructive defaecation where the rectum doesn't evacuate effectively (often related to pelvic floor abnormalities). If it is more frequent than three times a day then this suggest bowel pathology such as colitis - particularly if it is associated with other symptoms such as abdominal pain. A fairly abrupt and persistent change in bowel habit, either constipation or diarrhoea, may be due to bowel cancer. So it's always worth seeking a specialist opinion for any abnormal bowel habit whether short or long-term.