To understand why an extreme detox can make people feel so sick, you first have to understand how detox really works. This is an oversimplified explanation, but the fundamentals are correct: Your liver filters toxins out of your blood, including pharmaceuticals, heavy metals, ammonia and chemicals.
Your liver then dumps these toxins into your upper GI tract as part of a bile mixture used for digestion. Importantly, this reintroduces these toxins into your digestive system, where they can be quickly reabsorbed through intestinal walls and cause acute toxicity where you are essentially being “re-poisoned” with the same exact toxins your liver just pulled out of your blood.
(Note: Your kidneys also remove many toxins and flush them out of your body through urine. This is why kidney function is so crucial to your health. The heavy metals cadmium and mercury cause severe kidney damage, by the way.)
If you are eating a holistic, whole-food diet at the same time your liver is dumping toxins into your GI tract, then food fibers will tend to capture those toxins and trap them, ultimately transporting them out of your body through bowel movements. But if you aren’t eating any fiber — for example, you’re on a “juice fast” or a “juice cleanse” — then you have a potentially huge problem: You have no fibers to trap the toxins your liver is dumping into your small intestines! So those toxins get reabsorbed right back through your intestinal walls and into your blood.