Because one of the ways your body eliminates toxins is via your stool, eliminating almost all the fiber from your diet would be an enormous disservice to, and could even impede, your body's natural detox pathways. It flushes out the toxins and cleanses your gut, thus preventing any digestive issues. As you can see from the two simple examples of Dr Juan Rivera Keto and milk thistle, things aren't quite as simple as painting with a broad brush and saying that detox supplements and diets simply don't work. While the detox evidence for -- say -- cayenne pepper and maple syrup juice really doesn't exist, evidence for other nutrients actually does exist. When you think about it, the idea of toxins being somehow reabsorbed by your body as they sit in your colon actually makes some sense. After all, rectal suppositories are used to rapidly administer drugs -- so if drugs can enter your bloodstream from your colon, it's certainly possible that toxins could be entering too.
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