Mostly lipopolysaccharides (LPS), part of the cell-walls of gram negative intestinal bacteria, which are left in the gut when those bacteria die. If the gut barrier is compromised, and under constipation, excessive amounts of it can pass into the blood stream and be a burden to several systems.What exactly are endotoxins
This is one of the reasons Peat recommends the raw carrot salad (or cooked bamboo shoots) for most people - to help carry out and reduce endotoxin absorption, and to be aware of foods that feed excessive bacterial growth (starches and many fibres). When it's a more serious issue, he sometimes recommends antibiotics to reduce bacterial numbers. And for constipation, well-aged cascara sagrada.