Obesity is a major health concern in the United States. With more than one-third of American adults being obese, doctors who specialize in bariatric medicine are seeking new ways to help their patients lose weight and avoid the complications of obesity. One area of research is how hormones influence weight gain, and whether hormone treatment can help you lose weight or prevent weight gain. Low testosterone levels are associated with obesity in some individuals, but you should ask your physician if testosterone plays a role in your weight problem.
Availability
Testosterone is a steroid hormone synthesized from cholesterol in your gonads. "The Merck Manual of Diagnosis and Therapy" states that about 40 percent of your testosterone is tightly bound to sex hormone-binding globulin, or SHBG, a protein in your bloodstream. Approximately 58 percent is more loosely bound to albumin, another circulating protein, and 1 percent to 2 percent remains free in your bloodstream. Only the free and albumin-bound testosterone fractions are available to your tissues, including your fat tissue.
Effects
Testosterone is a metabolically active hormone in both males and females, but many of its physiologic effects result from its conversion to estrogen in your tissues. Testosterone enhances protein utilization, increases muscle mass and helps regulate your immune system. Estrogen --- derived from enzymatic conversion of testosterone --- improves bone mass and influences brain function. According to an August 2010 "Journal of Obesity" review, higher testosterone levels are responsible for development of abdominal fat stores in adolescent males. Conversely, fat deposition in older males is associated with testosterone deficiency.
Paradox
The seemingly paradoxical effects of testosterone on fat accumulation in adolescent males and older men may stem from age-related changes in hormone receptors in visceral fat. Although testosterone initiates abdominal fat accumulation in young males, continued testosterone stimulation does not seem to be necessary for maintaining these fat stores. As men age, their testosterone levels fall and their body fat percentage tends to increase. Male bariatric patients exhibit lower testosterone levels than non-obese men, and men who suffer from hypogonadism -- "testicular failure" -- tend to become obese. However, it is not clear if low testosterone levels contribute to excess fat storage, or if excess body fat somehow contributes to low testosterone levels.
Women and Testosterone
If you are female, your ovaries produce estrogen and progesterone -- and smaller amounts of testosterone -- throughout your reproductive life. Upon reaching menopause, your estrogen and progesterone levels fall, and testosterone exerts a more predominant influence. The Study of Women's Health Across the Nation, completed in 2006, demonstrated that obesity in a woman's menopausal years can be predicted by higher, not lower, testosterone levels. This may simply reflect a "catch-up" phenomenon, where testosterone is stimulating abdominal fat deposition in a more typical male pattern. In younger women, polycystic ovary syndrome is a condition characterized by obesity and high testosterone levels.
Considerations
Morbidly obese men --- those who may become bariatric patients --- tend to have lower testosterone levels than non-obese men of the same age. In contrast, obese women often exhibit higher testosterone levels than their non-obese counterparts. While there are compelling associations between low testosterone levels and obesity -- particularly abdominal obesity -- in certain populations it is not clear if low testosterone levels contribute to obesity in bariatric patients. Ask your doctor if low testosterone is an issue for you.
References
- Centers for Disease Control and Prevention: Obesity and Overweight
- "The Merck Manual of Diagnosis and Therapy, 18th Edition: Male Reproductive Endocrinology"; Mark H. Beers, M.D., Editor-in-Chief; 2006
- "Journal of Obesity"; The Role of Testosterone in the Etiology and Treatment of Obesity, the Metabolic Syndrome, and Diabetes Mellitus Type 2; F. Saad, L.J. Gooren; August 2010
- "American Journal of Epidemiology"; Reproductive Hormones and Obesity: 9 Years of Observation from the Study of Women's Health Across the Nation; K. Sutton-Tyrell, et al.; June 2010
