Testosterone and Fat Loss - Total Testosterone

TRT is often marketed for its near-miraculous ability to melt fat and build muscle. It definitely has an effect on your body, but is it all that? Learn the truth about testosterone and fat loss so you don’t get sucked in by the hype.

Read Time:

14–22 minutes

Table of Contents

1. Introduction

It feels like there’s a lot of content circulating right now talking up TRT’s transformative powers (or “TRT”, as sometimes people use the same label as a way to discuss much higher doses than actual prescribed TRT would entail), with impressive before and after photos and promises to burn away hundreds of pounds of fat.

The truth is, it actually can do all that and more. Testosterone has some incredible effects on the body. But it can’t do all that on its own.

And that’s been bugging me – that this marketing material slips the ‘if supported by healthy diet and regular exercise’ into the sub-text (if it’s mentioned at all), and leads you to the conclusion testosterone = fat loss.

It particularly bugs me that this is done under the label of ‘TRT’. Remember that proper TRT only restores the body to a normal level of testosterone. Look around next time you’re out and take a quick mental survey. What does the normal/average man look like? Don’t focus on the healthy specimens, look for a true, population-wide, average. Because the latest data from the NHS shows that the average man in England is overweight [1]. In fact, breaking it down by age the only group that isn’t overweight on the whole is 16-24 year olds, and even so 36% of them are. There are similar stories in the USA [2], Canada [3], Australia [4] and across the EU [5].

And the misconception isn’t just there for medical TRT either – many in the steroid community know the value of the extremely hard work and strict dieting that they follow but their community hubs are full of people looking for guides to a quick fix, or the stories of people who didn’t get the basics right before hopping on and wasting their cycle. Even the supraphysiological (that is, more than natural) doses used here don’t mean fat melts away and muscle piles on from the comfort of your couch.

So let’s get into it. How does testosterone affect our weight, and what really happens when we add TRT or higher doses?

2. The Testosterone-Weight Connection

‘Weight’ is a deceptively simple word for something made up of multiple components. This article is focused on fat, but fat and muscle are closely linked (and not just in the mirror), as you’ll see.

Testosterone interacts with muscle mass in two ways – it prevents it being broken down when our bodies don’t think they need as much of it (‘anti-catabolism’), and of course helps build more of it when it’s needed (‘anabolism’).

Testosterone’s muscle-promoting anabolic effects come from the way it interacts with muscle cells (and even the DNA inside them), convincing them to lay down more muscle fibre, and filling them with more nuclei.

You may remember a textbook picture of a cell as a blob with a single nucleus in it which contains the DNA. Like much of school-level science that’s broadly true, but in reality nature is far more nuanced than that. Some cells, such as muscle cells, can contain multiple nuclei (myonuclei, for muscle cells)- this gives them more copies of your DNA, which means more chemical factories to produce all the proteins demanded of them. A cell like this is called a syncytium.

The physical stress of exercise activates a satellite cell.
It divides and one or both of its daughter cells can become myoblasts.
- A myoblast is like the seed of a muscle cell.
- It’s got a nucleus and some basic machinery and is primed to produce muscle, but it’ll do nothing on its own.
The myoblast finds a mature muscle cell and fuses with it, adding its own nucleus to the many other myonuclei inside the mature cell.

(See [6] and [7]).

Testosterone modifies practically every step of this process ([8], [9] and [10]):

It makes the satellite cells more sensitive to activation.
It makes the satellite cells’ daughters more likely to become myoblasts.
It helps myoblasts fuse with mature muscle cells.
It boosts the production of muscle proteins from the newly-absorbed myonucleus.

But there are processes constantly trying to break down our muscles too. All proteins face degradation as they age, this is just normal wear and tear. The body has agents that detect and flag these out-of-shape proteins for breakdown. But in times of stress (such as illness, or a calorie deficit) the body will also activate certain proteins such as Atrogin-1 and MuRF1 that seek out muscle proteins specifically to be broken down (so their amino acids can be liberated for other uses). Testosterone limits the production of these proteins and so protects muscle, this is its anti-catabolic effect.

Muscle tissue takes a lot of energy to maintain, so by boosting the amount of it we have, testosterone can also increase the amount of energy our bodies use just to keep things ticking over – the basal metabolic rate (‘BMR’).

Testosterone also makes existing cells burn more energy. It stimulates the production of a protein called PGC-1α, which in turn can activate a number of other proteins which produce more mitochondria in our cells [11], and help shuttle fats from our fat reserves into those mitochondria.

So overall, testosterone can contribute to more muscle being built and more energy being burnt (which means less fat stored).

Testosterone has a direct effect on our fat cells as well. We produce an enzyme called lipoprotein lipase (‘LPL’), which anchors on to the linings of our capillaries and snatches fats circulating in our blood and breaks them down into smaller components (fatty acids) which can be pulled into cells. Muscle cells will try to use these fatty acids as fuel, while fat cells pick them up for storage. Testosterone reduces the amount of LPL we produce in fatty tissues and interferes with its anchoring to capillary walls, so that ultimately we pull less fat into our fat cells ([12]). Meanwhile, it boosts the amount of LPL produced in muscle, helping it to vacuum up fatty acids for fuel ([13]).

But the body can have an effect on testosterone too.

Fat cells produce an enzyme called aromatase, which converts testosterone into estrogen (specifically, a form of it called estradiol). Testosterone that’s been converted into estradiol is no longer available to do its job. This isn’t normally a problem- the reason we produce aromatase in the first place is because we need a certain amount of estrogen to be healthy. It has many protective effects ([14]), and even contributes to our metabolism ([15]). But men don’t need much estrogen, and as we get fatter it can pretty easily shift the balance too far.

As well as being made from our testosterone, estrogen acts on the Hypothalamus-Pituitary-Testicular Axis (the ‘HPTA’, which governs our natural production of testosterone) to shut down further production. This is why obesity is so often associated with low testosterone.

With less testosterone being produced, and more of it being converted to estrogen, levels drop and we lose many of the metabolic benefits described above. This leads to less energy being used and, if our diet isn’t adjusted in line with that, excess calories and therefore more fat storage. And so the feedback loop begins.

So it makes sense, then, as so many influencers and clinics are implying, that an obese and hypogonadal man starting TRT will interrupt that feedback loop, start gaining lean mass, have his metabolism boosted and look like a Greek god in a few months?

Not quite – mechanistically, yes, you might be able to construct that story. But the real world is more nuanced than that. We can put numbers against all this, and see what really happens.

3. What the Evidence Says: Testosterone and Fat Loss

Since there’s such a complex relationship between testosterone, estrogen, body composition and metabolism it’d be difficult to truly pick apart the issue from studies that only show correlations between all of those variables. Luckily, there have been some intervention studies done. Rather than looking at large numbers of men and seeing how they all look/behave on average, intervention studies take a small number (because they’re much more expensive to perform), control as many factors as they can, change something being studied, and observe the effects. This has a very good chance of telling you that by changing variable x you caused outcome y.

And there’s a couple of papers that established the effects of testosterone on male body composition. These are kind of core canon papers, and were performed by overlapping groups of researchers with similar controls.

One paper ([16]) took a group of healthy (eugonadal, non-obese) young men, suppressed their natural testosterone production, and assigned them one of five different doses of testosterone enanthate for 20 weeks. The doses given were either 25, 50, 125, 300 or 600 mg/week. 125mg/week would be a fairly representative TRT dose and kept the participants at around the same levels as they were before the experiment – it represents ‘normal’. 25 and 50mg/week doses kept their participants at levels that would be considered low, while the higher doses were definitely supraphysiological. They were all kept on a standardised (relative to their individual weights) diet, and asked not to take part in any weightlifting, or more than light cardio.

The power of this study is in laying out the relationship between testosterone and body composition, rather than in treating patients (since before the study these were all healthy young men, they didn’t come to the study with the accumulated effects of years of aging, let alone hypogonadism).

This study showed a few key points.

Firstly, that low testosterone (in the 25 and 50mg/week groups) increased fat mass by about 3 kg over the 20 weeks. This was a ‘significant effect’ – that doesn’t necessarily mean it was a big effect, it means that statistically it was very unlikely to be noise – ie, the change was big enough that it was almost certainly related to the experiment. The supraphysiological doses showed a slight reduction (1-2kg), but this wasn’t significant. The group given 125mg/week showed no overall change in fat mass. Again, this wasn’t a ‘significant’ effect, but that will partly be down to the fact that it showed no change – if nothing happens its very difficult to prove it is or isn’t because of the intervention. But since this was the group that maintained ‘normal’ testosterone levels for the experiment it certainly makes sense.

The point to take away from that is that even when putting healthy men with ‘normal’ testosterone levels onto supraphysiological doses of 300 or 600mg/week, with a maintenance diet and no exercise, they only lost a few pounds of fat over 20 weeks. So even ‘steroid’ doses did not cause massive fat loss – in fact they barely caused any fat loss.

In fact, they caused weight gain. The 125mg/week and higher groups all gained a few kg of lean mass. From +3.4kg to +7.9kg. As we established earlier, this might have an effect on their BMRs, but how big an effect? Well, a general rule of thumb is that a kilo of lean mass uses 13 calories a day [17], so even the group on the biggest dose that saw the biggest increase in lean mass would only have been burning 103 extra calories a day by the end of the experiment. 100 calories are very easy to ‘accidentally’ eat, but against an otherwise perfectly controlled diet 100 calories/day could add up to some meaningful weight loss – about 10lbs / 4.7kg over a year. It’s meaningful, but it’s no miracle drug.

Let’s look at the other paper now ([18]). This time they took a group of hypogonadal men and gave them 100mg/week testosterone enanthate for 10 weeks. Again, they were on a standardised diet and asked to refrain from exercise. This took their testosterone levels from 2.5nmol/L to 17.7nm/L, so effectively ‘treated’.

So what happened to them? They all gained weight. On average, 4.5kg over the 10 week study (or 1lb/week). This was pretty much entirely from lean mass, which increased by 5kg. Any changes seen in fat mass or body fat percent weren’t ‘significant’. Obviously there is a 0.5kg balance to make up there – changes in water retention are a confounding factor, but the bottom line is the same – TRT treatment didn’t cause very much fat loss.

This is further supported by a large meta-analysis [19], which looked at multiple papers studying the effect of testosterone on body composition. Over an average of 9 months the studies found, overall, -1.6kg fat loss, which was perfectly balanced by a 1.6kg increase in lean mass.

These papers together show the key takeaway for people considering TRT or steroids for fat loss – without exercise or a proper diet, these drugs won’t on their own melt fat away like you might be hoping.

Group	Dose	Duration	Lean Mass Change	Fast Mass Change
Hypogonadal	100mg/week	10 weeks	+5kg	Negligible
Healthy	25mg/week	20 weeks	-1kg	+3.1kg
Healthy	50mg/week	20 weeks	+0.6kg	+3.5kg
Healthy	125mg/week	20 weeks	+3.4kg	Negligible
Healthy	300mg/week	20 weeks	+5.2kg	-0.5kg
Healthy	600mg/week	20 weeks	+7.9kg	-1.1kg

Table 1: Testosterone’s effects on body composition, summarised from Bhasin 2001 and 1997 ([16], [18]).

4. Diet & Exercise

If testosterone doesn’t have much effect on fat, even at supraphysiological levels, where are all the miraculous transformations coming from?

The answer is exactly where we’ve been told to look to for changes in our physiques since time immemorial – healthy diet and reasonable exercise. That advice isn’t sexy so it gets glossed over, but it’s the essential component.

A moderate calorie deficit of -500cal/day, achieved either through calorie restriction, increased activity or a combination of both, will lead to weight loss of about 1lb/week. In fact, it doesn’t even need to be exercise – Non-Exercise Activity Thermogenesis (‘NEAT’) is the energy we burn by being active but not from exercise – simply walking around and living our lives, doing our jobs, brushing our teeth. Obviously, for men with manual jobs this can be a lot, but it’s a surprisingly large use of our calories even for the more sedentary of us. And it’s fairly easy to increase without, by definition, having to exercise – park further from your destination, take the stairs instead of the elevator, drink more so you have to get up and pee more, or take an evening stroll.

This small calorie deficit absolutely dwarfs any changes caused by testosterone replacement or supplementation. And while 1lb isn’t much, it adds up. It doesn’t even take that long to add up to something significant either – you might want to lose 50lbs and think ‘that’s a whole year away’. But your first 10lbs are only a couple of months away.

The journey of a thousand miles begins with a single step.

Or…

The best time to plant a tree was 20 years ago. The second best is now.

5. Make the Most of your Testosterone: Lift Weights

If you’re willing to put in the effort, then testosterone does offer one synergistic route to ‘faster’ results ([20]).

Recall that much of its effect on metabolism comes from its ability to enhance muscle development. Without the initial stimulus to trigger that muscle development a lot of its potential benefits will be wasted. So for restored or enhanced individuals, make the most of that pathway by giving your muscles stimulus to grow. That means strength training with progressive overload – generally, weight lifting.

Testosterone will make the most that your body can of the training stimulus provided from weightlifting, promoting of course muscle size and strength, but over time that additional muscle will edge up your BMR.

That’s not to say you should completely ignore cardio – it has important benefits for the cardiovascular system. I’m just making the point that if you’re looking for something to ‘make the most’ of your TRT, strength training is more synergistic.

If you’re considering TRT or other forms of testosterone enhancement hoping it’ll melt pounds of fat away and pile on muscle, you’re going to be sorely disappointed.

But if you’re willing to put up with a different kind of soreness – that from a well used muscle, then you might be able to achieve your goals.

Testosterone at any level simply isn’t as transformative as it’s often made out to be. But it can support a healthier lifestyle. This is its true superpower – as a motivating agent. If you’re a new or prospective TRT patient then you’re committing to a lifetime of treatment, that’s a powerful statement that you care about your health. Strike while the iron’s hot and take this chance to sort your diet and start exercising, and you’ll be in a much better position even just one year from now than if you started treatment and changed nothing. To say nothing of 10 years down the line. And besides the initiatory trigger, when your TRT kicks in you will likely find you have a bit more energy and vitality that you may want to find an outlet for – channeling them into a healthier lifestyle is an excellent choice.

And if you’re not a TRT patient but are thinking that testosterone might offer an easy route to a bigger, leaner physique, why wouldn’t you get the foundations right first? While we saw that supraphysiological levels increase lean mass, yet another paper by the researchers from our two earlier papers ([20]) showed that the combination of testosterone and exercise had an outsized effect. Steroids carry health risks, especially in higher doses, are expensive and are probably illegal (based on your jurisdiction) – why would you leave the greater gains on the table by taking the lazy route?

6. Conclusion

Testosterone protects muscle from degradation in times of stress (such as during a calorie deficit).
It boosts the development of muscle tissue.
Muscle tissue burns more energy than fat tissue.
Testosterone also encourages our cells to produce more mitochondria, and fuels those mitochondria more readily.
So testosterone does ‘boost your metabolism’.
But these effects are very subtle.
Months-long studies failed to show any meaningful reduction in fat mass, either in restored hypogonadal men or in healthy men given supraphysiological doses of testosterone, without the addition of exercise.
Starting TRT will not transform your body dramatically without other lifestyle changes – diet and exercise.
But if you’re hoping for a leaner, bigger body, TRT may provide the energy and the motivational spark to make those lifestyle changes and stick with them.

Testosterone protects and builds muscle – it doesn’t melt fat.