Some men believe that testosterone may assist in fat loss. Classically speaking, testosterone is responsible for the masculinity of men. It also promotes muscle mass growth in both genders.
Most men have enough testosterone. However, some men may experience low levels of testosterone.
So, if you are one of those men, have a lot of questions about testosterone replacement therapy and its effects, want to know the link between TRT and weight, then stay with us!!!
In this article, we gathered all the answers to the questions, you may have in mind. Stay tuned!!!
- Lifestyle modifications are considered a cornerstone in managing obesity.
- Testosterone therapy offers safe and effective treatment strategy of obesity in men with testosterone deficiency.
- Testosterone therapy increases lean body mass, reduces fat mass and produces sustained and significant weight loss, reduction in waist circumference and BMI.
Testosterone is an essential, vital sex hormone for males, required for differentiation, and developmental growth. 
Testosterone is an anabolic hormone and its known actions on muscle growth and function have long been exploited by athletes. 
Normal Testosterone Levels
In young, healthy men (20 – 30 years old), the normal levels of serum testosterone (400 – 700 ng/dL) are controlled by the feedforward and feedback components of the hypothalamic-pituitary-gonadal axis and are maintained within the normal range of 300–800 ng/dL. 
Aging and Testosterone Levels
Several studies have shown that Serum testosterone levels decline gradually with age in men after the third decade of life at an approximate rate of 1-2% per year, varying from one to another, and are affected by several factors such as adiposity and chronic diseases. 
Low Testosterone Levels
Obesity is a major public health threat that has an enormous economic burden on society, with an estimated economic impact of greater than $2 trillion. 
In the USA, about 35.5% of adult men are obese.
Obesity impacts quality of life and shortens life expectancy. Obesity increases the risks for atherosclerosis, diabetes mellitus, metabolic syndrome, non-alcoholic fatty liver disease, and cardiovascular system disease. 
Grades of Obesity
Obesity is categorized into three grades on the basis of patients’ BMI.
- Grade I: BMI ranging from 30 to 34.9 kg/m2.
- Grade II: BMI ranging from 35 to 39.9 kg/m2.
- Grade III: BMI more than 40 kg/m2.
Low Testosterone and Weight Gain
Obesity contributes to the decline of testosterone levels and the prevalence of hypogonadism is more than 70% in excessively obese men. 
Low baseline testosterone predicts obesity in men and normalization of physiological testosterone levels reduces the activity of lipoprotein lipase and tryglycerides. 
Mulligan et al. reported that approximately 52.4% of all obese men had testosterone levels below 300 ng/dl (10.4 nmol/l). 
Similarly, Luconi et al. suggested that approximately 75% of men with obesity grade III awaiting bariatric surgery had hypogonadism. 
Testosterone levels are reduced with increased waist circumference and obesity. 
Approximately 40% of obese non-diabetic men and 50% of obese diabetic men aged above 45 years have low free testosterone. 
The data from recent studies with longterm testosterone therapy in male hypogonadism, using testosterone formulations which result in sufficient circulating normal testosterone levels and good patient adherence, reported significant and sustained significant weight loss, reduced BMI, and waist circumference. 
Data reported from three registries, in which long-term testosterone therapy was evaluated in men with testosterone deficiency and varying grades of obesity, suggested that testosterone therapy is effective in producing weight loss in all three grades of obesity. 
Testosterone and Body Composition
There is a significat inverse correlation between total and free testosterone levels and obesity and waist circumference. 
Waist circumference and waist-to-hip ratio are commonly used as a proxy measure of abdominal fat that is often considered to correlate more with pathological consequences of obesity. 
Testosterone and Adiposity
Rather than obesity per se being related to testosterone levels in men, adiposity and particularly the location of adipose distribution appear to influence both androgen concentrations and cardiovascular risk. 
Loss of androgen receptor function increases the number of adipocytes and the accumulation of visceral fat. 
Vermeulen et al. reported that testosterone levels were negatively correlated with percentage body fat, abdominal fat and insulin levels in a study of 57 men aged between 70 and 80 years. 
Abate et al. reported that subcutaneous fat accumulation in the truncal area is highly predictive of low plasma concentrations of free testosterone rather than visceral adiposity. 
Testosterone and Lean Muscle Mass
In addition to increased adiposity, a decrease in lean muscle mass is a key feature of obesity that is fundamental to the metabolic dysregulation that contributes to metabolic syndrome and cardiovascular risk. 
Low levels of testosterone are therefore unsurprisingly linked to a loss of muscle mass in men.
Several cross-sectional studies have reported an association between serum levels of testosterone and muscle mass in men with higher levels of testosterone associated with less loss of lean muscle mass in older men. 
In several studies of older men with low levels of testosterone at increased risk of frailty, exogenous testosterone supplementation is shown to be associated with increases in lean body mass and decreases in fat mass. 
The HORMA (Hormonal Regulators of Muscle and Metabolism in Aging) trial investigated the effects of testosterone supplementation in a population of 112 community dwelling elderly men (65–90 years) with testosterone levels in the low-normal range over 16 weeks of treatment. 
This study showed an increase in total lean body and appendicular skeletal muscle mass associated with increased testosterone levels. 
Testosterone Replacement Therapy and Obesity
Testosterone therapy in hypogonadal obese men has been suggested as a novel approach for the treatment of obesity. 
Several studies have shown that the correction of testosterone levels in obese men reduces weight, BMI, WC and fat mass. 
Low baseline testosterone was found to predict subsequent weight regain over 26 weeks of follow-up, after an initial 8-week low-calorie diet and exercise-induced weight loss in men. 
An initial weight gain in response to testosterone therapy may be a result of water retention, which is transient. 
Testosterone replacement has substantial effects on body composition. Replacement doses of testosterone increase body weight, primarily by increasing fat-free mass. 
We would like to point out that in all the reported studies to date, testosterone therapy should result in weight gain not weight loss.
However, the reduction in fat mass, coupled with improved metabolic function and increased vigor and physical activity over time in response to testosterone therapy produces the observed weight loss. 
Effects of Testosterone Replacement Therapy on Obese Males
- Fat mass reduction.
- Increase lean body mass.
- Weight loss.
- Reduces waist circumference and body mass index (BMI).
Metabolic Effects of TRT on Obese Men
Long-term testosterone therapy in obese men reduces blood glucose, HbA1c, CRP and improves lipid profiles. 
Testosterone therapy in obese men reduces the fat content in the liver and improves liver function. 
Testosterone treatment results in improved insulin sensitivity, lipid oxidation and reduction in fat mass with concomitant gain in fat free mass. 
Previous study reported that the marked and significant improvements in various metabolic parameters clearly indicate improvement in metabolic function, as reflected by decrease in inflammatory biomarkers and improved liver function. 
These findings combined with the improvement in lipid profiles, blood sugar, blood pressure and urogenital function support the reported improvement in quality of life assessed by the AMS questionnaire and the improvement in lower urinary tract symptoms assessed by the IPSS questionnaire. 
Significance of TRT Timeframe
The effect of testosterone treatment in hypogonadal men is mostly well-received, although its effects are not often apparent in short timeframes and often require longer periods to observe metabolic effects. 
How Long Does It Take To Lose Weight on Testosterone?
Systematic meta-analysis of studies investigating testosterone therapy in hypogonadal men revealed that changes in fat mass and lean body mass occur within 12–16 weeks, stabilize at 6–12 months. 
Cohorts of hypogonadal subjects receiving long-acting testosterone undecanoate showed an almost 5% decrease in body weight in the first year of treatment and greater than 13% after 5 years. 
Testosterone and Weight Loss
Intervention measures, such as diet and exercise or surgical treatment of obesity, results in increased testosterone levels. 
Weight loss as a result of diet, exercise or bariatric surgery can significantly increase testosterone levels in men. The increase in testosterone is proportional to the amount of weight lost. 
Lifestyle changes produce modest weight loss in the early stages of weight management strategies, but a high rate of recidivism is observe. 
Although lifestyle modifications are highly recommended, as integral part of strategies designed for treatment and management of obesity, in most patients, such strategies are not always successful in the long term because of high rate of recidivism, in part due to lack of adherence to prescribed regimen. 
Bariatric surgery is able to produce substantial and sustained weight loss and ameliorate several obesity-related comorbidities. 
Bariatric surgery produces improvements in the cardiovascular disease risk-factor profile, including metabolic syndrome, a lower risk of ischemic heart disease and mortality. 
Bariatric surgery increases levels of total and free testosterone concomitant with reduction in weight, BMI and waist circumference. 
These findings strongly suggest that weight reduction via bariatric surgery is associated with normalization of hormonal profiles in obese men. 
It should be emphasized that only carefully selected patients can be subjected to bariatric surgery and patients need to be followed-up very closely and carefully.