The DAO Enzyme, Explained: Why Some People React to Leftovers

Diamine oxidase, or DAO, is the enzyme your gut uses to break down histamine from food. When you do not make enough of it, dietary histamine builds up and spills into circulation — causing flushing, headaches, hives, and that unmistakable racing heart after eating.

This is why leftovers are such a common trigger: histamine accumulates in food as it ages. The fresher the food, the lower the histamine load.

Supplementing DAO shortly before meals gives your gut extra enzyme to degrade that histamine before it causes a reaction. It does not cure the underlying issue, but for many people it is the difference between eating freely and living on a tiny list of safe foods.

One critical warning: be careful with probiotics. Strains like L. casei and L. bulgaricus actually produce histamine and can make everything worse. Choose histamine-neutral strains instead.