What term describes a substance that fights excessive oxidation of molecules in the human body?

The term that describes a substance that fights excessive oxidation of molecules in the human body is "antioxidant." Antioxidants play a crucial role in protecting cells from oxidative stress, which can result from an overproduction of free radicals—unstable molecules that can damage cellular components and lead to various health issues, including aging and chronic diseases.

Antioxidants neutralize free radicals by donating an electron, which stabilizes these reactive molecules and prevents them from causing further damage. Common antioxidants include vitamins C and E, selenium, and various phytochemicals found in fruits and vegetables. Their protective functions are vital for maintaining overall health, as they help to reduce inflammation, support the immune system, and promote healthy aging.

Other terms in the choices relate to the oxidation process but do not directly describe the substance that combats oxidative stress. An oxidant refers to a substance that can oxidize other molecules, while free radicals are products of oxidation that can cause damage. A free radical scavenger is another way to describe antioxidants but is less commonly used as a standalone term. Thus, "antioxidant" is the most accurate and widely recognized term in this context.