ratio of food ingested to fecal matter expelled

Agnes,Bob,or Lillian,
I am wondering if there are any statistics on the percentage of weight which a healthy body absorbes from the food that is taken in. For example if a healthy body ingests 1 lb of food, how much of that weight is expelled through the bowels or bladder? Does the body just take the nutrients which are basically weightless? I am not really sure how to best pose the question so I'll apply it to my husband. Since we have been cleansing and changing our diet to more and more raw foods he has slowly been gaining weight, which is great for him because he is very physically active and has had problems with being too thin. I on the other hand have been slowly losing weight, which is just fine with me!

He has always had regular bowel movements even with a questionable diet. I guess I am confused about how the body puts on mass when so much is regularly expelled through the bowels. Seems like he would have to be eating so much more in order to have gained weight.

We've basically ruled out parasites as we have been doing a bowel/ parasite cleanse for some time now and he just continues to be regular with good quality bowel movements.

Just curious about a process I don't quite understand.