Reader TTS

WHAT IT DOES: The main sex hormone for men (initiating puberty and fertility and influencing body composition and libido), it also affects mood, cardiovascular health and more. THE BODY

WEIGHT CONNECTION: Testosterone encourages muscle formation and tamps down body fat. Starting in a man's 20s and 30s, levels of this hormone naturally drop about 5 to 10 percent per

decade. Does this drop drive up body fat? “Maybe just a little, but the research isn't definite on this. However, in hypogonadism, which is diagnosed by finding a low testosterone level

in men with symptoms like low libido, depression or signs like anemia or osteoporosis, men tend to have a lower percent of muscle and a higher percent of fat, especially visceral fat,” says

Joshua Thaler, M.D., associate professor of medicine in the Division of Metabolism, Endocrinology and Nutrition at the University of Washington. HORMONE RX: If your testosterone levels are

normal, do nothing. “Getting extra hormone probably won't change body composition and can have harmful side effects such as prostate enlargement and worsening cholesterol,” explains

Thaler. But if you're diagnosed with hypogonadism, you should consult your doctor about the potential benefits of testosterone treatment. “It might take off a few pounds, especially

around your midsection, but don't expect the treatment to completely reverse overweight or obesity,” says Thaler. LEPTIN WHAT IT IS: Leptin is derived from the Greek word for “thin,”

because rising levels of this hormone signal the body to shed body fat. Leptin also helps regulate blood sugar, blood pressure, fertility and more. THE BODY WEIGHT CONNECTION: Emitted by fat

cells, leptin serves as a recon system, alerting the brain to both gains and losses in body fat. As you pack on more fat, leptin levels rise, dialing down appetite while boosting metabolic

rate — which helps put the brakes on weight gain. “But for reasons that are not clear, in people with obesity there's a breakdown in the signaling. They have high levels of leptin that

aren't doing a good job of suppressing appetite,” Thaler explains. The opposite happens when you lose body fat: Leptin levels drop. “This sends a starvation signal to the brain,

prompting the metabolic rate to slow and appetite to increase. This was useful during times of famine, but it's definitely not helpful to people who are trying to maintain weight loss,”

Thaler says. HORMONE RX: In 1999, when a 9-year-old, 208-pound girl with a voracious appetite triggered by leptin deficiency received leptin injections, it was life-changing. Her appetite

normalized and she began losing weight. “The study created a splash, but it turns out that leptin deficiency is extremely rare. And leptin injections don't do anything for the rest of

the population with obesity,” Thaler says. Bottom line: There are no leptin therapies that work for obesity, at least not yet. GHRELIN WHAT IT IS: Called the “hunger hormone,” ghrelin is

secreted by the stomach when you haven't eaten for a while, traveling up to the brain where it whets your appetite. It also helps keep things moving through your digestive tract and is

involved in the cardiovascular system, immune system and mental health. THE BODY WEIGHT CONNECTION: Just as leptin levels fall with weight loss, ghrelin levels rise, making weight loss all

the more challenging. HORMONE RX: NADA. “You'd think that blocking ghrelin would quell appetite and induce weight loss, but ghrelin-blocking medications have had mixed results in animal

studies, although the research continues,” says Thaler. INSULIN WHAT IT IS: Released by your pancreas in response to the rise in blood sugar (glucose) after eating, this hormone helps

spirit away excess glucose into muscle and fat cells. In muscle, glucose is burned as fuel or stored as glycogen. In fat cells, it can be burned, or converted to fat.