Men often try to boost their existing testosterone levels through exercise alone, whether it be weightlifting or another form of working out. While exercise by itself is good for weight loss, studies show that testosterone replacement therapy (TRT) promotes fat loss and encourages muscle building in men. Research shows that excess belly fat triggers estrogen production in men which can hurt their existing testosterone levels. When men start to lose body fat and gain muscle mass through TRT therapy, their body begins to produce more testosterone again.