The question is a conflation. “Obesity” isn’t a single cause, it’s a cluster of at least two distinct things that lower testosterone, and you have to measure them separately to know what you’re actually dealing with. First is the aromatase activity in adipose tissue. More fat mass means more enzymatic conversion of testosterone to estradiol.
That’s the one everyone knows. Your T is literally being turned into estrogen. Second, and the part people usually miss, is the effect on SHBG (sex hormone-binding globulin). The hyperinsulinemia that often comes with obesity suppresses hepatic SHBG production.
Low SHBG means your total T looks low, but more importantly, it means testosterone is cleared from your system faster. The half-life of your endogenous T effectively shortens. So you have a production issue confounded by a clearance issue. Just pulling a Total T lab is measuring the downstream result of both of those problems at once.
You can’t tell how much is conversion vs how much is clearance. You’re measuring something, but it’s not the root cause you named it. To untangle it, you need the right panel. Total T, Free T, SHBG, and a sensitive estradiol (E2).
That’s the minimum to start seeing which lever is actually pulling the numbers down.