Probably ingredients like garlic. Garlic and other plants contain substances that neutralize heterocyclic amines. Research has focused on a group of substances known as dietary phenolics. Phenolics is a broad category that includes flavonoids, flavonols and catechins. These guys possess antioxidant activity, but their protection against HCAs is due to a different mechanism.
Phenolics work by changing the way HCAs are metabolized.
Just as estrogen can be metabolized different ways by the body, HCAs can too. Phenolics have the power to change the way HCAs are metabolized so that carcinogens are not created in the process. HCAs are normally broken down by p450 enzymes. Unfortunately, although the enzymes are natural to our bodies, HCAs are not. In trying to eradicate the strange invaders, p450 inadvertently turns them into carcinogenic substances.