It is estimated that digestion takes about 50 hours. It takes about 6-8 hours for food to pass through your stomach into the small intestine and then on into your large intestine and finally elimination. [Mayo Clinic]
The range of frequency of bowel movements is very broad — 3 times a week to 3 times a day.
Now when an American adds fiber to their diet, transit time is reduced and bowel movements more frequent. [FAO] However, many Americans mischaracterize this increase in visits to the toilet as diarrhea. It is loose stool. Diarrhea is expulsive and often associated with infection (parasites, viruses, bacteria).
Another control factor for bowel frequency is calcium and magnesium. Calcium induces constipation and magnesium induces loose stool (not diarrhea). Calcium citrate is used to alleviate constipation or to clean stool from the intestines in preparation for surgery. [WebMD] Attempt to use fiber to overcome constipation may be fruitless if this is the case.
It has recently been reported that implantation of beneficial bacteria into the gut (intestines) significantly helps individuals with chronic constipation. [Archives Medical Research July 4, 2016]
I once spoke to a woman on the phone who thought it was entirely normal to defecate once every two weeks. Women do have more difficulties with constipation than men.
With this in mind, researchers in Japan studied frequency of bowel movements and found that fewer bowel movements increased the risk for cardiovascular disease mortality (hey, that makes constipation a life-and-death issue, doesn’t it?).
Death from cardiovascular disease rose 20-40% as bowel movements were once every 3-4 days compared to once a day. [Atherosclerosis March 2016]
Based upon that study, one would think a bit faster transit time (the time it takes for food to travel from your mouth to exit as waste) would be desirable. However, another study shows that when a bowel movement (BM) was reported every 2-3 days versus every day, the risk for colon-rectal cancer declined. [British Journal Cancer April 2004] Another study came to a similar conclusion. [American Journal Epidemiology 2010] This contrary finding might be explained by lack of adequate time to absorb nutrients.