Which of the following is not considered a dietary supplement?

Pro-hormones are not classified as dietary supplements but rather as substances that can affect the body's hormonal balance. They are often used to enhance athletic performance or promote muscle growth by converting into active hormones. This regulatory distinction places pro-hormones under different scrutiny and guidelines than typical dietary supplements, which are intended to support dietary intake, enhance health, or provide additional nutrients.

In contrast, amino acids, metabolites, and plant extracts are all considered dietary supplements. These substances are commonly taken to support various physiological functions, improve health outcomes, or enhance performance in the context of exercise and nutrition. Supplements such as amino acids can aid in muscle recovery and protein synthesis, while plant extracts often contain beneficial compounds that may have antioxidant or anti-inflammatory effects. Since these categories align with nutritional support and health enhancement, they fall under the broader definition of dietary supplements.