A protein found in raw egg whites that binds very tightly to biotin (a B vitamin) and prevents the body from absorbing it.
From Latin 'avidus' (eager, greedy) + chemical suffix '-in', named because the protein 'greedily' grabs onto biotin molecules and holds them so tightly.
This is why eating raw eggs can cause biotin deficiency in some animals—avidin is so good at capturing biotin that cooking eggs destroys avidin, releasing the vitamin so your body can use it.
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