A review of literature by Arturo Figueroa from Florida State University and colleagues concluded that L-citrulline and watermelon reduces resting blood pressure, and chronic use may increase endurance. Citrulline is an important amino acid involved in the formation of urea. It is a popular component in athletic food supplements because it participates in key amino acid reactions and influences blood flow by increasing nitric oxide levels. Nitric oxide (NO) is an important chemical secreted by the inner lining of the blood vessels that controls blood flow throughout the body. NO is vital for muscle blood flow, sexual function, fuel and hormone delivery to muscles, tissue oxygenation, and general energy levels. Other studies found that citrulline increases brown fat activity, which increases caloric expenditure and promotes fat burning. Citrulline increased levels of hormone-sensitive lipase by 150 percent, which promoted fat mobilization and use. Citrulline is an underappreciated supplement that improves fat burning and muscle blood flow and protects the gut from injury during exercise.

(Current Opinion in Clinical Nutrition & Metabolic Care 20:92-98, 2018)