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Using Testosterone To Reduce Abdominal Fat |
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Written by By Dan Gwartney, MD
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Friday, 30 January 2009 |
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Page 6 of 8
Fat cells also metabolize sex steroids. Testosterone can be converted to estrogen via the enzyme aromatase, created from androstenedione via an enzyme known as AKR1C3 or deactivated via the enzyme AKR1C2. An elegant study reported in the Journal Clinical Endocrinology revealed a strong association between body mass index (BMI) and aromatase (as measured by mRNA) in subcutaneous fat cells; a weaker association between aromatase and body fat percentage was also present.18 The authors noted that the association with body fat percentage would likely have been stronger if a more precise measure was used, as opposed to the impedance method.
In clearer terms, the study showed that people were heavier and fatter if their fat cells increased estrogen content by increasing aromatization. This would decrease both testosterone (since aromatase uses testosterone to make estradiol) and the testosterone:estradiol ratio. Several papers have reported increased circulating estrogen levels in obese people, often speculating that the increased estrogen concentration is a result of an increased fat mass.19-21 From the results of this study, it appears that the estrogen-obesity cycle is self-propagating, as one leads to the other, as suggested by other researchers.22
Estrogens act on the fat cell by activating two different classes of the estrogen receptor, ??and ?? The ?-class of the estrogen receptor (ER?) when occupied by estradiol stimulates another class of receptor called ?2A-adrenergic receptor.23 This is the receptor blocked by yohimbine, which is used in several fat-loss supplements. When ?2A is activated, it inhibits lipolysis, making it more difficult for the fat cell to release stored fat. Conversely, testosterone increases the density of ?-adrenergic receptors, which increase lipolysis and the release of stored fat.10
To date, many studies have observed a fat-loss effect when replacement doses of testosterone are given to men— young and old, healthy or ill.13-16 One study has even documented a further benefit in giving supraphysiologic testosterone to young men, in that it reduced visceral fat, which is more strongly associated with cardiovascular disease and insulin resistance.17 Clearly, there is an interaction between sex steroids and obesity that is underappreciated.
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Research and Review 
