How Testosterone Levels Affect Muscle Growth and Fat Loss

Higher testosterone levels are often equated with more muscle growth and fat loss. Is it that simple?

If you ask the average gymgoer what single physical factor most affects muscle growth and fat loss, they would probably answer “testosterone levels.” And they’re right.

Testosterone is certainly a primary hormonal driver of muscle growth. Research has shown that anabolic steroids, which drastically raise testosterone levels, given to even young, healthy men can induce muscle growth and fat loss without any exercise whatsoever.

Thus, it would be fair to assume that the higher our testosterone levels are, the more muscle we build and the leaner we get, right?

Testosterone Levels and Muscle Growth

We already know that dramatically elevating testosterone levels induces muscle growth.

Yes, if you take enough of the right steroids, your testosterone levels will skyrocket, and if you lift weights regularly, you will be able to achieve more muscle growth than if you were drug-free.

But here’s something that most people don’t know:

Fluctuation of testosterone levels within the physiological normal range does not affect muscle growth.

That is, if your testosterone levels are right-down-the-middle normal, and you increase them to a high-normal, you may feel a little better and notice a boost in libido…but it won’t enable you to build more muscle.

I know that sounds kind of blasphemous, but it’s actually been scientifically proven.

Charles R. Drew University of Medicine and Science conducted and published a study about a decade ago wherein they administered varying amounts of  testosterone enanthate along with drugs to inhibit natural testosterone production to young, healthy men for 20 weeks.

While higher testosterone levels did produce greater muscle gains, it wasn’t as pronounced as you might think.

What researchers found was that so long as testosterone levels were within the physiological normal range, between 300-1,000 ng/dl, muscle growth didn’t change very much. That is, the subjects on the low end of normal weren’t that far behind subjects on the high end in terms of muscle growth.

A statistically significant increase in muscle growth wasn’t seen until testosterone levels surpassed the top of “normal” by about 20-30%.

Now, this study does have a limitation: subjects weren’t exercising. While total amounts of muscle and strength gained would clearly have been higher if they had been weightlifting, the relationship between testosterone levels and overall muscle growth would still be seen.

This was partially demonstrated by another study, this time conducted by McMaster University with young, resistance trained men.

Subjects lifted 5 times per week for 12 weeks, and followed a standard dietary protocol (high-protein intake, post-workout nutrition, etc.). The primary finding of the study was that the exercise-induced spikes in anabolic hormones like testosterone, growth hormone, and IGF-1, which all remained within physiological normal ranges, had no effect on overall muscle growth and strength gains.

That is, all subjects made gains in muscle, but the variations in the size of the hormone spikes among them had no bearing on the results.

The key takeaway here is not that you should take steroids, but that things you can do to naturally raise your testosterone levels are unlikely to affect your muscle growth.

And speaking of steroids, the above findings are in line with steroid research as well.

For instance, researchers at Maastricht University conducted an extensive review of literature related to the use of anabolic steroids and found that the muscle gains in people engaging in resistance training while on anabolic steroids mostly ranged between 2-5 kg (4.5-11 pounds) over the short term (less than 10 weeks). The largest amount of muscle growth researchers found was 7 kg (15.5 pounds) over 6 weeks of weightlifting while on steroids.

The point is this:

Even steroids don’t always dramatically increase the amount of muscle you can build (it depends what you take, in what dosages, and for how long), so what does that tell us about how fluctuations of testosterone in the normal physiological range relate to muscle growth?

As I talk about in my article on the best supplements for muscle growth, this is why buying natural testosterone boosters for muscle growth purposes is a complete waste of money. Even if they work (and most don’t), it’s just not going to help you build more muscle.

The only exception might be someone whose testosterone is at the absolute bottom of the physiologically normal range, or even below that, and who is then able to naturally increase it to the top of the range. That person would probably notice an improvement in muscle growth, not to mention overall well-being, libido, cognitive function, and so forth.

Now, I’m not saying that there’s no reason to do anything to naturally improve your testosterone levels. Improving muscle growth just isn’t on the list. Losing fat, however, is…
Testosterone Levels and Fat Loss

Unlike muscle growth, researchers at the Charles R. Drew University of Medicine and Science did find that fluctuations of testosterone within the physiological normal range had significant effects on body fat percentage.

The higher the testosterone levels, the leaner subjects were. And conversely, the lower the testosterone levels, the fatter they were. When researchers decreased certain subjects’ testosterone levels from the baseline average of 600 ng/dl to around 300 ng/dl, they saw a dramatic 36% increase in fat mass.

Although the exact mechanisms behind this aren’t fully understood just yet, research has show that testosterone directly inhibits the creation of fat cells and that low testosterone is a contributing factor to obesity.