Answer:
Not to much, no. Semen is sometimes swallowed during the sexual act of fellatio, but it doesn't amount to much; a little salt, some trace of protein,nothing that would hurt your diet. And as a man, you expend very little energy in sex,worth no more than 150 calories.
From a weight-loss perspective, it isn't all that good; you'll probably consume more calories getting ready for sex than you can consume during the sex itself.
But even if it isn't a good weight-loss plan, a surprisingly large number of people DO have sex, and fairly frequently too.