Can losing weight help to rise your testosterone level in a man 40 yrs old?

I think this effect is more apt to occur when overweight or obese men lose weight by proper dieting. Exercise also plays a role. An endocrinologist can advise you best though.

Several studies have shown it can.

An enzyme called aromatase is present in obese individuals that causes testosterone levels to decrease and be converted to a small level of estrogen. Losing weight and working out at a gym, especially lifting weights will increase your testosterone levels.