The Obesity and Stool Volume Question

In order to have a chance at getting to the bottom of Joe’s recent fascination with stool volumes of the obese and dead movie star cowboys. I want to clearly define the question so that we are all on a level playing field.

As I understand it, the question is: Do obese people have a greater output of stool than normal weight people? This question insidiously crept into his mind after years of noticing that when he finds himself in airport restrooms to do the deed in question, which is apparently a frequent occurrence, the number of obese individuals also there to relieve themselves does not seem to be proportional to the number of obese individuals in the general population at the airport.

I will first say that there are far too many factors in this question to resolve with any simple “thought experiments” or by polling friends and family of varying stature. But since that is about as far as I am willing to go with it, that is what we are stuck with.

My answer: Larger people, who eat more, have larger stools. There may be some questionable variables there, such as what is the size difference of the compared individuals, what are the various individuals eating, and is there weight relatively stable?
If you say that their weights are stable and they are eating the same types of food, then it stands to reason that the larger people will produce more feces.

As luck would have it, I was recently able to discuss this with a patient of mine who lost about 150 pounds. The answer was that the frequency of bowel movements decreased from twice daily, like clockwork, to once every two or three days. There was no observation of apparent stool size per defecation, but it was noted that the consistency went from solid and well formed to "soft serve". The confounding factor is that this patient had a crippled GI tract due to gastric bypass surgery. I have another patient who is undergoing a large weight loss, without surgery so once the weight has stabilized I may inquire further. Now that I think about it though, I would probably have much more luck finding individuals who have gone from normal weight to obesity to ask these questions, but I am afraid they might be a little less excited to talk about it.

Another questionable variable is regarding the measurement of stool. Should it be by weight or volume? Differences in gut flora, hydration status and many other factors could potentially produce a large variation in stool volume for an equivalent weight and without any significant difference in effective waste removal. I think I might have to vote for dry weight as the standard.