One ill-conceived strategy sometimes used for rapid weight loss is consumption of laxatives, which are designed to soften fecal matter, making it easier to defecate. Because defecation can make one feel lighter or less full, some people think that using laxatives can help them to lose weight.

This abuse of laxatives can permanently damage the large intestine, leading to dependence on laxatives for bowel movements, dehydration, and increased risk of colon cancer.

Questions

1. Fecal matter is composed of fiber and other indigestible food remnants. It is present in the large intestine, until defecation. Laxatives act on the large intestine to hasten the expulsion of feces, which occurs after nutrients have been absorbed by the small intestine. Would the loss of food that cannot be digested lead to permanent weight loss?
2. If you step on a scale before defecating, you may weigh a bit more than after defecation. However, if the digestive tract is really just a tube with openings at the mouth and anus, is food that does not get absorbed by the small intestine ever really part of your body?
3. Losing weight involves the loss of fat. What gas do you breathe out when fat is metabolized?
4. In light of your answer to the previous question, how might exercise help with weight loss?
5. Consider your answers to questions 1–4 and explain why the original statement bolded above sounds right, but isn’t.