Why does salt water function as a laxative?

From the ancient Egyptians to modern hippies doing the "Master-Cleanse" diet, salt water has been used as a laxative for thousands of years. But I can't seem to find any scientific information as to *why* it works.

The Master-Cleanse diet asserts (along with all sorts of other dubious ramblings about "toxins") that sea salt water is a much more effective laxative than iodized salt water. But I can't imagine why this would be the case...

Osmosis. You put salt within the bowel lumen and it "calls" water, which freely passes through the bowel cell membranes. That creates osmotic watery diarrhea. It's how Fleet Phospho soda and magnesia milk work. Plus, it's also why some sweeteners (polyalcholic such as maltitol) can give one the runs.

That makes perfect sense. I would guess also then that iodized salt would work as well as sea salt, since it's just osmosis... Perhaps some of the other trace minerals in sea salt also have osmotic properties, but it shouldn't matter, only the concentration should matter. Right? Report It

Right! Any strong salt can do it even in low doses, while weaker salts (like magnesium citrate) work through the same mechanism but for higher dosages. Report It

I can't either. The salt should remove water from your system, which would cause the opposite effect as a laxative.