The male libido is largely influenced by testosterone. The more testosterone you have, the thinking goes, the more likely you are to get sprung at the slightest sexual thought or nuance, the briefest glimpse of thigh or contour of a breast, or hell, even a chalk doodle on the sidewalk that vaguely resembles the curves of a female body.

However, according to a study presented at a meeting of urologists in Boston, it appears that total testosterone has little to do with male libido. Instead, it's free testosterone and, surprisingly, the ratio between testosterone and estradiol (a type of estrogen) that determines your randiness.

How They Figured It Out

The scientists had 200 patients of a cardiology practice fill out a series of erectile dysfunction questionnaires, including the IIEF-15, which collectively spell out a pretty decent picture of a man's libido.

Of note is that none of the men had been diagnosed with hypogonadism (low testosterone) in the past, and none were on medications that could have affected testosterone levels.

The researchers then measured the patients' total testosterone, estradiol, sex hormone binding globulin (SHBG), and free testosterone and compared them with their reported libidos.

What They Found

It turned out they found no correlation between total testosterone and how often (or how infrequently) the men wanted to do it. Nor did estradiol levels correlate independently with sex drive, even when levels were lower than 5 ng/dL. This last fact is significant because it was thought that men are more likely to have healthy libidos if their estradiol is in the "sweet spot" between 2.0 and 5.5 ng/dL.

What did correlate with libido, though, was the ratio of testosterone to estradiol, along with free testosterone, i.e., that percentage of testosterone that isn't chemically bound to SHBG. The higher the free T, presumably the greater the sex drive.

What This Means to You

Oftentimes, men with low libidos or poor sexual functioning go on testosterone replacement therapy or pro-testosterone supplements. Sometimes it works and sometimes it doesn't, but when it doesn't, it's generally because of one of two things, as this study clearly supports:

  1. Too much SHBG (resulting in low levels of free testosterone)
  2. High estrogen levels (throwing off the testosterone/estrogen ratio)

What the study didn't tell us is the perfect level of free testosterone or the precise T:E ratio we'd want for "optimum" sex drive, which would be difficult as hell to define, anyhow. Still, it gives us some clues as to what we should do.

For instance, if you have symptoms of low testosterone (depression, weight gain, inability to put on muscle, diminished sexual desire or performance) or symptoms of high estrogen (increased abdominal fat, fatty tissue around the nipples, erectile dysfunction, or loss of libido), you might consider finding a progressive physician and getting your SHBG and estrogen levels tested (along with free T, of course), the latter with what's known as the "sensitive" assay.

If you don't ask for a "sensitive assay," they're going to measure your estradiol the same as if you were a ballerina from the Bolshoi ballet suffering from menstruation problems. In other words, the results will be pretty much useless.

Your other choice would be to experiment with using dietary practices and supplements to manipulate levels of SHBG and estradiol.

How to Lower SHBG and/or Raise Free Testosterone

  1. Take magnesium daily to raise free testosterone.
  2. Take zinc daily to lower SHBG.
  3. Take vitamin D3 daily to lower SHBG.
  4. Don't short-change yourself on carbs. A diet low in carbs increases SHBG while lowering testosterone.
  5. Watch the booze so that testosterone levels don't drop.

How to Lower Estradiol Levels

  1. Lose fat. Fat contains an enzyme that converts testosterone into estrogen.
  2. Eat lots of broccoli, cauliflower, cabbage, and Brussels sprouts. They contain a chemical that "fights" estrogen.
  3. Take curcumin. It reduces the effects of an enzyme that converts testosterone to estrogen.
  4. Take resveratrol to decrease the activity of that estrogen-converting enzyme.
  5. Don't get old. The older you are, the more estrogen-ey you are. (Okay, if you insist on aging, then at least put the above tips into action.)

Related:  Keep Estrogen Under Control

Related:  The Complete Guide to T Replacement


  1. Gupta, N., Goldberg, H., "Calculated Free T and T:E Ratio but not Total Testosterone and Estradiol Predict Low Libido," AUA Annual Meeting, May 12-16, 2017, Boston.