Every day we are exposed to a variety of chemical substances: environmental toxins, medications, hormones from food and the body's own waste products. How efficiently our body neutralizes and excretes these substances is highly individual – and genetically determined.
Detoxification in the liver runs in two phases: In Phase I (controlled by the CYP450 enzyme family), fat-soluble toxins are chemically "activated". In Phase II (e.g., GST genes), these intermediate products must be immediately bound to molecules like glutathione and made water-soluble.
Some people are genetic "slow metabolizers" (e.g., CYP1A2). They break down caffeine extremely slowly and get palpitations or sleep disorders from coffee. Others (fast metabolizers) can drink espresso before going to bed.
Genetics is not fate. Knowing your predisposition allows you to get the best out of your biology through a targeted lifestyle.