Estrogen blockers are designed to maintain healthy testosterone levels and prevent estrogen levels from increasing. As men age, the amount of aromatase in their systems rises. Aromatase is the enzyme that converts testosterone into estrogen – and could lead to muscle wastage, fat gain, low libido, low mood and more. Estrogen blockers are said to contain aromatase inhibitors which may help balance users’ hormones and reverse the effects of low testosterone. The could result in more lean mass, improved metabolism and greater strength. Common natural estrogen-blocking ingredients include indole-3-carbinol (found in green vegetables), and chrysin (found in honey, bee propolis and passionflower).