Visceral Fat, Not BMI, Tracks With Low Testosterone

A cross-sectional analysis published July 13, 2026 in the Journal of the Endocrine Society answers a question a lot of men have put to their doctors: if my weight is fine, why does my testosterone look like this?

The short version is that BMI was never measuring the thing that matters most. Where your fat sits appears to separate testosterone levels more sharply than how much of it you carry.

What the analysis found

Karl Friedl and Adam Potter, researchers at the U.S. Army Research Institute of Environmental Medicine, analyzed 4,948 US men aged 20 to 59 from the 2011 to 2016 National Health and Nutrition Examination Survey. All of them had a morning total testosterone measurement. Of those, 4,492 also had a valid measure of visceral adipose tissue (VAT), the fat packed around the organs behind the abdominal wall, taken by DXA scan.

The researchers then did something BMI-based screening cannot do. Within each BMI category (normal weight, overweight, and obese), they compared the quarter of men carrying the most visceral fat to the quarter carrying the least.

• Within every BMI category, men in the highest visceral fat quartile had 33% to 36% lower total testosterone than men in the lowest quartile.
• Sorted by waist circumference instead of BMI, the gap was 25% to 39%.
• Normal-weight men with high visceral fat had testosterone levels comparable to obese men with low visceral fat.

The authors' conclusion: "Testosterone deficiency in some men appears to be a phenotype of visceral fat biology rather than obesity per se."

That third bullet is the one worth sitting with. Two men of the same height and weight can land in different testosterone territory entirely, based on whether their fat sits behind the abdominal wall or under the skin. If your intake screening stops at BMI, those two men look identical on paper.

SHBG explains a large share of the gap

This is the mechanism piece, from the same paper. When the researchers added sex hormone-binding globulin (SHBG) to their statistical models, explanatory power more than doubled: pseudo-R-squared rose from 0.18 to 0.45. They describe this as partial mediation, meaning SHBG appears to sit on the path between visceral fat and testosterone rather than being an unrelated bystander.

SHBG is a protein that binds testosterone as it circulates. A total testosterone result counts the bound and unbound hormone together. So when SHBG shifts, total testosterone shifts with it, without that number telling you how much hormone is actually available to your tissues.

This is not a new idea in clinical practice. The Endocrine Society's 2018 clinical practice guideline already recommends obtaining a free testosterone level, by equilibrium dialysis or an accurate formula, in men whose total testosterone sits near the lower limit of normal or who have a condition that alters SHBG. The same guideline recommends diagnosing hypogonadism only in men with symptoms and signs plus unequivocally and consistently low morning fasting total testosterone, confirmed by repeating the measurement.

What the NHANES analysis adds is scale. It suggests a meaningful number of men carrying visceral fat at a normal BMI fall into exactly the category where the guideline says total testosterone alone is not enough to go on.

The assay changes what a panel can detect

A second 2026 paper makes the measurement question sharper. In the European Male Ageing Study, published July 30, 2026 in the European Journal of Endocrinology, researchers looked at 526 community-dwelling men (mean age 70.5) and compared three ways of expressing testosterone against sexual function outcomes.

Free testosterone measured directly, by equilibrium dialysis followed by LC-MS/MS, was associated with erectile dysfunction, fewer intercourse attempts, lower orgasm frequency, and reduced sexual desire. Calculated free testosterone was associated with only two of those four. Total testosterone was associated with none of them.

That is a cross-sectional finding in a group of older European men, so it does not establish cause and does not automatically transfer to a 35-year-old. But it points the same direction as the NHANES paper: the number your panel reports depends on which number was ordered and how it was measured.

Some of it appears to move without hormone therapy

A 2024 meta-analysis in Andrology pooled 44 studies covering 1,774 participants, with a median follow-up of 26 weeks, to estimate what weight loss did to testosterone in men with obesity. Across those participants, low-calorie diets were associated with an average rise in total testosterone of about 2.5 nmol/L, and bariatric surgery with about 7.2 nmol/L. Free testosterone rose by roughly 19.9 and 58.0 pmol/L respectively. Gains tended to be larger in men who started with a higher BMI or lower baseline SHBG and testosterone.

Those are averages observed in the studies' participants, not a forecast for any individual, and the included studies spanned a wide range of starting BMI and testosterone values. Still, it establishes that adiposity-associated low testosterone is at least partly movable.

What this means if you are that man

If you have symptoms consistent with low testosterone and a normal BMI, and you have been told your weight is not the problem, that conclusion was drawn from a measure that does not see visceral fat. Body composition and SHBG are reasonable things to raise with a licensed provider, alongside the repeat morning total testosterone the guideline calls for. If a workup does confirm low testosterone, what to do about it, including how enclomiphene compares with testosterone therapy, is a separate conversation worth having once you have real numbers.

The honest limits: the NHANES analysis is cross-sectional, a single snapshot in time, so it cannot show that visceral fat causes low testosterone rather than traveling with it. It used one morning testosterone measurement, not the confirmed repeat that a diagnosis requires. DXA visceral fat scanning is a research measure, not a routine clinic test. And the study covered US men aged 20 to 59, so it says nothing directly about men older than that.

None of this tells you that you need treatment. It tells you which questions make a workup honest.