The fruit of the plant looks like a small, green pumpkin and is used in many traditional Asian dishes for its sour flavor. In the skin of the fruit, there is a large amount of a natural substance called Hydroxycitric Acid (HCA). This is the active ingredient in Garcinia Cambogia extract… that is, the substance that produces the weight loss effects. Bottom Line: Garcinia Cambogia is a plant often used in Asian recipes. The skin of the fruit contains a substance called Hydroxycitric Acid (HCA), which is the active ingredient.