This isn't a glamorous topic, but it's worth considering briefly to complete our understanding of the rubber bag. Every day, you put in some quantity of food and drink. For the most part, your body efficiently disassembles these complex substances into their molecular constituents and makes them available to power the cells of your body. As in any chemical process, there's a residue of waste, and your body excretes this in the well-known ways.
As an omnivore, your body is very efficient. You can use all kinds of odd stuff as food. Conversely, the substances your body can't use--the discard pile of the chemical card game of metabolism--are genuinely nasty stuff; the sooner you're rid of them the better.
Unfortunately, as you bring your weight down to your personal optimum level, the reduced quantity of food you're eating and the odious chemicals released as you burn up excess fat create a tendency for these poisons to stay inside the rubber bag. Means to ameliorate this situation will be discussed, tastefully I hope, later on.