Tribulus has long been known for its potential benefits in increasing various hormones, however, recent studies have shown that Bulgarian Tribulus is the only 100% effective strand of Tribulus. Clinical studies in Bulgaria have shown Tribulus terrestris to increase the sex hormones LH (luteinizing hormone) level by 72% and the body's own free testosterone level by 41% in healthy adult males in only five days. LH regulates the testosterone production in the testes and high levels of LH coincide with high testosterone levels. One reason men get bigger around their waist as they get older is because they struggle to secret testosterone. As testosterone suppresses LPL, an enzyme that works on the fat cells in the abdominal walls, decreased testosterone production means increased fat production.