An awkward question. Bear with me...

In terms of mass, what percentage of the food that we eat do we end up excreting? Of course, it depends on a whole host of factors so lets assume a healthy average build/height male with a balanced diet in his 30s who doesn't drink or smoke.

I ask this because I am quite intrigued by my own bowel movements (typically 2 or 3 days apart and average in size - I have no problem passing them btw they've just never been that regular). I know my bowels are not excercised like most other adult males but what's more intriguing is that when I do finally "go", it looks like and feels like I've hardly eaten over the past few days! Take this weekend for example, it's fair to say I've been overdulging and overeaten but by the end of this week I will probably "see" only 10% of that in the toilet.

  • $\begingroup$ It depends on what you eat. Not everything can be absorbed. Cellulose for example is not digestible by humans cause of missing enzymes and its a big part of every plant. Nevertheless your digestive system needs something to work on. Pure starch or glucose if its not too much would be totally absorbed. If you eat a lot of white bread and meat but almost no vegetables this could be a reason. $\endgroup$
    – Oli4
    Commented Feb 16, 2015 at 14:47
  • $\begingroup$ Very little of what you excrete actually come from food. $\endgroup$
    – One Face
    Commented Feb 17, 2015 at 8:29
  • $\begingroup$ By conservation of mass, almost all solids that you excrete come from food. $\endgroup$
    – March Ho
    Commented Feb 23, 2015 at 7:12

1 Answer 1


It very much depends on what specific kind of food you are taking. Say, if we eat more green vegetables then we are supposed to excrete more compared to a highly meat-rich diet.
Also, it depends on the food-intervals, more the interval more the absorption by body so less amount going out(but giving extreme interval is not good either).
All depends on the need of body, if body needs more than what you are giving to your body it gonna obviously excrete more.
And always keep in mind to take sufficient water, because without it all things go malfunctioning in our body.

  • 1
    $\begingroup$ Can you provide a citation that a longer meal interval allows a greater amount of absorption? $\endgroup$
    – March Ho
    Commented Feb 23, 2015 at 7:13
  • $\begingroup$ link this may be of some use @MarchHo $\endgroup$
    – diffracteD
    Commented Feb 23, 2015 at 12:56
  • $\begingroup$ Can you give an example based on an average american diet? Guesstimate $\endgroup$
    – larry909
    Commented Jun 25, 2023 at 11:37

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