Testosterone and Metabolism: Separating Hype from Evidence

Fitfluencers on TikTok tout testosterone as the ultimate metabolism hack, claiming more testosterone means more muscle, increased fat-burning, and an effortlessly speedier metabolism. While there’s truth to the connection between metabolism and testosterone, the science is far more nuanced.

Studies suggest that TRT can positively affect body composition by increasing lean muscle mass and reducing fat mass, as well as enhancing insulin sensitivity in men with low testosterone levels.

These metabolic benefits weren’t automatic, though—lifestyle factors like strength training, diet, and sleep quality still played a critical role. This highlights what many experts emphasize: Testosterone isn’t a miracle metabolism booster, but in men with low T, it can be a powerful tool for optimizing metabolic health.

About the Experts

Joshua Calvert, M.D. a board-certified urologist who specializes in men’s hormone care

Steven Wise, M.D., a board-certified endocrinologist with over 25 years of experience

How Testosterone Increases Metabolism

Testosterone plays a key role in regulating metabolism, influencing how efficiently your body burns calories and processes energy. It does this in several ways:

• Increases muscle mass
• Reduces body fat
• Increases motivation to exercise
• May reduce free fatty acid production and improve mitochondrial function

Get Your Energy, Muscle, and Love Life Back

And all the other benefits that come with raising your testosterone safely.

Let’s Get Started

Testosterone increases muscle mass

Testosterone is a key player in muscle growth. And since muscle burns more calories than fat tissue, adding muscle can slightly boost your metabolism while you’re at rest and during exercise. ¹

Testosterone stimulates the release of insulin-like growth factor 1 (IGF-1), which activates muscle stem cells and triggers hypertrophy—the process of building bigger, stronger muscle fibers. ^{2 3}

The hormone also suppresses the activity of myostatin, a protein that inhibits muscle growth. ⁴

But testosterone replacement therapy (TRT) isn’t a shortcut to building muscle—just a tool. To see a real metabolic boost, you need to strength train consistently to build lean muscle. The numbers vary from study to study, but on average, each pound of lean muscle burns five to six extra calories per day. ^{5 6} In one small study, men ages 19 to 47 who took TRT for 12 weeks gained five pounds of muscle—but that’s much harder to do as you age. ⁷

That said, lifting does more than tweak your metabolism. It strengthens bones, protects against injury, and improves longevity. If you’re on TRT, combining the two is a win-win.

Testosterone reduces body fat

Testosterone doesn’t just build muscle—it also reshapes how your body stores fat. Some research suggests it curbs visceral fat, the dangerous kind that wraps around your organs and raises your risk for metabolic syndrome, diabetes, and heart disease. ⁸ Other studies suggest it reduces subcutaneous fat—the soft, pinchable fat just under your skin. ⁹

The mechanism? Testosterone appears to suppress proteins that regulate fat cell development, stopping preadipocyte cells from maturing into fully developed fat cells. ¹⁰ Less fat translates to a leaner body composition over time.

Fat loss itself can drive testosterone levels higher. That’s because body fat—especially visceral fat—converts testosterone into estrogen via an enzyme called aromatase. Less fat means less conversion, keeping more testosterone in circulation. ¹¹

Testosterone increases motivation

Testosterone rewires your brain. Higher levels are linked to greater motivation, persistence, and drive. Scientists have found testosterone receptors in key brain regions that regulate mood, decision-making, and reward-seeking behavior—which could explain why higher testosterone is associated with greater motivation to train and make healthy food choices.

One study found that men with higher testosterone levels were more driven to achieve goals in athletic training. ¹² Another experiment in men ages 18 to 40 found that a single dose of TRT increased competitiveness and persistence, even when participants knew they were up against a stronger opponent. ¹³

Part of this effect comes down to dopamine, the brain’s primary motivation chemical. Testosterone boosts dopamine levels, which can increase your willingness to exercise, eat well, and stick to healthy habits. ¹⁴

Testosterone may reduce free fatty acid production and improve mitochondrial function

You may have seen bold claims that TRT tamps down free fatty acids (FFAs) and supercharges mitochondrial production. But the evidence here is thin.

FFAs are fat molecules that circulate through your bloodstream. High levels are associated with obesity and type 2 diabetes. ¹⁵ Some research suggests that low testosterone correlates with higher FFA levels, while TRT may help lower them—potentially improving insulin sensitivity and reducing body fat. ¹⁶

Then there’s mitochondria, cellular factories that break down food into usable energy. Low testosterone can impair mitochondrial function, decreasing fat oxidation and reducing how much energy your body expends at rest. ¹⁷ It’s not surprising, then, that some studies have shown TRT may increase mitochondrial synthesis, stabilizing insulin levels and increasing metabolism. ¹⁸

However, urologist Joshua Calvert, M.D., says more research is necessary to validate testosterone’s role as a direct metabolism regulator.

“Some studies show testosterone inhibits FFA production and some say it increases lipolysis—the process that breaks down fat into FFAs,” he says. As for mitochondria, testosterone may be one piece of the puzzle, but it’s not a magic bullet.

Metabolic Health vs Metabolic Rate

Metabolism (or metabolic rate) is about how many calories your body burns each day. Metabolic health is about how well your body processes those calories—and whether it’s working in your favor or against you.

Think of it this way: Your metabolic rate is like an engine—it determines how much fuel (calories) you burn. Metabolic health, on the other hand, is about fuel efficiency. “It’s shaped by insulin sensitivity, blood sugar control, lipid metabolism, and inflammation and cholesterol levels,” says Calvert.

He adds that you can have a fast metabolic rate but poor metabolic health. Someone who burns a lot of calories can still have insulin resistance, high triglycerides, or chronic inflammation—key drivers of metabolic dysfunction.

Because it increases muscle mass and improves insulin sensitivity, TRT may help you optimize both metabolic rate (how much energy you burn) and metabolic health (how well your body processes it).

Testosterone improves insulin sensitivity

Testosterone may help your body better respond to insulin and, in turn, head off metabolic health risks.

Men with low testosterone are twice as likely to be insulin resistant—meaning their bodies struggle to regulate blood sugar—than those with normal levels of the hormone. ¹⁹

Over time, this increases the risk of prediabetes and type 2 diabetes. Nearly 90 percent of men with low testosterone experience metabolic syndrome, a cluster of five metabolic risk factors: central obesity (high waist circumference), triglycerides, blood pressure, fasting blood glucose, and low high-density lipoprotein (HDL) cholesterol. ²⁰

Scientists aren’t completely sure why testosterone influences insulin resistance, but there are two leading theories:

• Testosterone strengthens insulin signaling, making it easier for cells to absorb glucose from the bloodstream. ²¹
• Testosterone reduces inflammation, lowering levels of inflammatory cytokines that are associated with insulin resistance. ²²

Whatever the mechanism, TRT may help insulin sensitivity. In a small study of men with type 2 diabetes, three months of TRT reduced insulin resistance, improved glycemic control, and decreased belly fat. ²³

“Although testosterone therapy is not the primary treatment for metabolic syndrome or other disorders linked to low T like insulin resistance, it can be a key component—along with diet and exercise—in making most of them easier to control,” says endocrinologist Steven Wise, M.D.

Natural Ways to Improve Metabolism

There’s a lot of misinformation about ways to boost metabolism. The truth? No single hack will dramatically crank up calorie burn—and anything that does work requires effort. Fortunately, the habits that support metabolism also improve health and longevity.

Exercise regularly

Two of the most effective workouts for metabolism are strength training and high-intensity interval training (HIIT). Both add muscle mass (even without TRT)—which naturally raises resting metabolic rate (RMR), or how many calories you burn while at rest.

• Strength training: One review found that 10 weeks of strength training increased RMR by 7 percent and lowered body fat by four pounds. ²⁴
• HIIT: Compared to low—and moderate-intensity workouts, higher-intensity exercise creates an afterburn effect called excess post-exercise oxygen consumption (EPOC) ²⁵. This means your body keeps burning calories long after your workout ends, as it works to restore energy levels. The “best” HIIT format is still up for debate, but one thing is clear: effort matters. If you’re doing intervals, push hard during the work periods to maximize the metabolic benefits.

Increase fiber intake

Fiber can help you feel fuller longer, reduce overall calorie intake, and support metabolism. Credit bacteria in your gut, which break down fiber into short-chain fatty-acids (SCFAs), which influence how fast your body burns fat, carbs, and protein.

Fiber also boosts levels of leptin, a hormone that regulates food intake, metabolism, and body weight. ²⁶ Aim for 38 grams of fiber per day from sources like vegetables, fruits, nuts, seeds, beans, and whole grains.

Get quality sleep

Everyone knows seven to nine hours of sleep is ideal, but restorative sleep matters more than total hours in bed. When you’re in bed but awake off and on throughout the night, it can impact insulin sensitivity, affect testosterone levels, and decrease metabolism. ²⁷

Lack of sleep also leads to an uptick in ghrelin—a hormone that increases appetite—and a reduction in leptin. ²⁸ These sleep hygiene tips may help.

Eat plenty of protein

Protein is one of the building blocks of muscle—and more muscle leads to a higher metabolism. ²⁹ The American College of Sports Medicine and Academy of Nutrition and Dietetics recommends 1.2 to 2.0 grams of protein per kilogram of body weight per day for active people. ³⁰ That’s 90 to 150 grams for a 165-pound male. If you’re looking to add muscle mass, aim for the higher end of this range.