Guy poops at same time every day - Psychological or Physiological?

Question:

I was talking to an old military guy about how he still wakes up at 4am every day without an alarm clock years after leaving the military. He went on to say that he poops at the same time every day. It seems unlikely that someone would need to poop at the same time every day and at no other time of day. Even if the person eats at the same time every day you would thing that various foods process at different rates. Aside from that it seems very unlikely that the body recognizes a 24 hour poop cycle, why not 16 hours or 32? 24 hours has an artificial significance to people. I'm thinking that the cause of a regimented poop time is more psychology than an actual need to poop every 24 hours like clockwork. My question has 2 parts:
Is a 24 hour poop cycle driven by psychology or physical need stemming from regularly scheduled eating / exercise times?

If you think the answer is that it is driven by psychology then what is the mechanism behind this? Why would it happen?

Answers:
I Like your question, but do not understand the intricacies of it. I like to take a dump when I wake in the morning, and therefore I do so.
I hate getting caught out in public places, with an uncomfortable feeling in my bowel.
I guess it's just a bit like if one blows one's nose properly first thing in the morning, there will be no need to pick it through the course of the day?
Am I making any sense?

It is physical, and actually a sign of good health.

Humans have a biological clock in them. It is created through habit. Although it can be changed or ignored. It exist in us all.
http://www.nimh.nih.gov/publicat/biocloc...
http://www.sfn.org/index.cfm?pagename=br...

I would have to say it is physiological. He probably has consistant eating habits in amount, time and diet.

Psychological: I do the same thing my body clock goes off at around the same time each morning (poop times..) This guy isn't lying that's normal 4 him.Oh yeah it's also normal 4 me..

Guy poops at same time every day - Psychological or Physiological?

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