Fish with yoghurt: myth and truth

Many people believe that eating fish with yoghurt or milk causes deadly poisoning, and avoid mixing them, so much so that "fish and yoghurt" has become a saying like "fire and water". Medically, though, there is nothing wrong with eating fish with yoghurt or milk.

The main reason for this myth is that fish and milk are both common causes of food poisoning. Both spoil quickly and are easily contaminated with germs and chemicals, so it is risky to eat either from an unreliable source. But people tend to link things the wrong way: they blame the mix of fish and milk instead of noticing that one of them had gone off.

That doesn't completely rule out a reaction to fish and milk eaten together when each is fine on its own. We can imagine the two reacting to form new substances that cause an allergy in some people, while each food alone causes no immune reaction.

Some people's bodies might treat the mix as a serious threat and react so violently that it could be fatal. This is extremely rare, but it may have helped create the myth. The share of people expected to be allergic to the mix is under 1%, and how severe a reaction is (if there is one) depends on how much is eaten. So the "crazy" among us can try the two together for the first time in a small amount, with an ambulance nearby, in case your body likes being one of the rare ones.

The immune explanation

White blood cells attack proteins that are foreign to them, triggering an immune reaction: antibodies against the protein and a large release of histamine. That is an allergy.

Milk proteins may not cause an allergy in some people, but they are known to bind foreign substances (such as minerals) very effectively. Proteins from fish could change the 3D shape of milk proteins, making them look foreign, so that white blood cells attack them and cause an allergy to the mix.

In general, we don't recommend trying this mix anyway, because it doesn't taste good…