Slimming diet masculinizes fat men | Meta-study
If men with more body fat than is good for them want to increase their testosterone levels, they can of course give themselves synthetic testosterone - with all the associated risks. An alternative approach is for them to reduce their fat percentage. This will also increase their testosterone levels.
In 2022, Stephen Smith, research manager at the Australian private research center Clinical Research Australia, published a meta-study in which he aggregated and reanalyzed the results of 7 previously published trials. In the trials, researchers had men lose weight for 1-52 weeks and determined the effect of this on their testosterone levels.
Losing weight increased testosterone levels, as you can see in the first figure below. But the increase in testosterone levels is only statistically significant if the test subjects are overweight at the start of their weight-loss diet. That's what the second figure illustrates.
Click on the figures for a larger version.
The figures above refer to the total testosterone level, not to the concentration of bioavailable testosterone.
It is possible that only part of the extra amount of testosterone that circulates in the body due to weight reduction is bioavailable. Losing weight also increases the concentration of SHBG in the bloodstream - although not to the extent that the concentration of total testosterone increases.
SHBG is a transport protein. Testosterone attached to SHBG is no longer active.
Smith suspects that a reduction in body weight increases insulin sensitivity. As a result, fat cells produce fewer factors that inhibit the release of control hormones in the brain. These control hormones stimulate the production of testosterone in the testes.
At the same time, a slimming diet ensures that fat cells convert less testosterone into estradiol and release fewer inflammatory proteins. These inflammatory proteins inhibit the production of testosterone in the testes.
Nutr Rev. 2022 Apr 8;80(5):1222-36.
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