According to the Re/Search Guide to Bodily Fluids (Paul Spinard, 1994), the average man produces about 3.5 mL of semen per ejaculation whose nutritional value is:
less than 1 calorie
150 mg. protien
11 mg. carbohydrates
6 mg. fat.
3 mg. cholesterol
7% US RDA potassium
3% US RDA copper
3% US RDA zinc
300 million spermatoza
(Someday men will have to have all this tattooed to the side of their hip, like a can of Coke or a box of Wheaties.)
It looks healthy enough per serving size, but when compared to breast milk (which has about 170 calories per cup), semen has about 40% more calories (about 230 calories per cup). High levels of fructose (fruit sugar!) is normal in the semen and this sugar comes almost entirely from the seminal vesicles.
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More Fun Sperm Facts
For the "average" man, the ejaculate contains over 80 million sperm. In addition to the little wiggly things, semen contains (taken from several web sites):
water
ascorbic acid (vitamin C)
blood-group antigens
calcium (yes, just like milk!)
chlorine (add your own little contribution to cleanliness!)
cholesterol (Is this the "bad cholesterol" or "good cholesterol"?)
citric acid, creatine, deoxyribonucleic acid, fructose, glutathione, hyaluronidase, inositol, lactic acid, magnesium, nitrogen, phosphorus and potassium (what do you know, these are good for fertilization too!)
prostaglandins (fatty acids that, while not a hormone, perform hormone-like functions)
purine, pyrimidine, pyruvic acid
sodium (good to have, especially if you've been sweating a lot)
sorbitol, spermidine, spermine
vitamin B12 and zinc (you would think it's a multivitamin)
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Random Sperm Facts
Average volume of semen per ejaculation: 1-2 teaspoons
Average number of times a man will ejaculate in his lifetime: 7,200
Average total amount of lifetime ejaculate: 18 quarts
Average speed of ejaculation: 28 miles per hour
Its muscle drives nature's only known rotary-joint. The tail SCREWS, not whips. (no pun)
Average number of calories in a teaspoon of semen: 7
Average duration of orgasm: 4 seconds
Average number of sperm cells in the ejaculate of a healthy man: 200 to 600 million
Distance sperm travels to fertilize an egg: 3-4 inches
Sperm lifespan: 2.5 months from development to ejaculation
I would put the URL but there is more "inappropriate" (but fun) stuff there.