Yes, Xizor pointed this out in MPSIMS, but I don’t understand why.
Fat does not turn into muscle, so does extremely rigorous cardio-vascular exercise reduce ALL the fat in one’s breasts?
It just seems…unlikely that that’s the whole story.
Or are the breasts not present because it’s a matter of self-selection?
They don’t have breasts because they have incredibly low body fat percentages (for that matter, they probably don’t have regular periods either.) and are probably on an extremely low fat diet. Boobs are fat. Hence, no fat in diet and low body fat = no boobs.
I think it’s a combination of very low body fat and pumped muscle. Many women BBs have breasts to speak of during “regular” times, though I doubt if it could be called a rack of epic proportions. When they pump to inflate the muscles before a competition (very high weight, low reps) the muscle under the breast tissue expands and pulls the skin and breast tissue making them flatter.
Wow, it almost hurt - pulling that reply out of my ass. 
Surely they are made of glandular rather than fatty tissue? How could fat secrete milk?
…oh, and as for the OP:
WAG but could it be a combination of self selection as suggested (poor self image over naturally small breasts for instance) plus (ab)use of steroids?
the “boob” part of the boob is basically decorative. The functional portion of the breast is fairly minimal, IIRC.
Because you never see the ones who do. If they have too large of breasts, then their pecs don’t show, and they never get out of the compulsories in the small competitions, much less make it to the professional ranks.
This from Ms. cornflakes, the vicarious Doper.
*Originally posted by spritle
Now, I’m confused again. I thought right before a competition BodyBuilderss do light weight and lots of reps to show more definition(to make the muscle look more defined so to speak?). So what is right here?
Low body fat percentage. The idea is to eliminate body fat so that the underlying musculature shows through. High repetitions with low weights and high levels of cardiovascular excercise also results in the abscence of mentrual periods, as was pointed out.
If she uses anabolic steriods that will also cause her breasts to diminish in size, her skin to coarsen, and her voice to deepen. It has the reverse effect in men, causing what are commonly called “bitch tits.” Also testicular atrophy, acne, and possible prostate enlargement.
Actually some do have breasts. Some had small breasts beforehand.
They don’t have periods anymore. So I would also assume that their hormonal production for breasts has also changed.
handy nailed it, but I just wanted to add a comment.
First, as handy said, some female body builders do have ‘normal’ breast sizes.
More importantly, many had small breasts before they got started in body building. In fact (and this is the point I wanted to make), the number one reason women get involved in body building is because they started out trying to use weight training to build up their chest sizes.
Therefore, the ‘population’ is biased towards women with small breasts. This is not to say that low body fat, supressed estrogen levels, steroid use, and other factors don’t play a role, as well.
rmariamp is correct. Mostly what you see is “fat storage units”. The glands are quite small and don’t begin production of milk (and thereby enlarge) until given the correct hormonal signal from the body during pregnancy.
If you’ll also notice, most don’t have that little “pooch” of fat at the lower abdomen that most women have. This is also an area where women store fat reserves.
As handy mentioned also, their periods are probably really screwed up too. Fat produces estrogen (or estrogen precursors) so a woman whose body fat is too low will have wacky or no menstrual cycles. When I was in the military, my body fat was down to about 18%, which is pretty low for a woman, and my cycles were very irregular. I think the normal % is about 23-25% for women.
Also, if a woman isn’t having periods her bone density drops a lot. After 5 years of this, she may have the bone density of a 70 year old woman.
The costs to the body for this sort of hobby is tremendous. Male body builders have an equal cost to their body as most muscles you see are mostly just scar tissue.
Do you have any evidence at all to back this up? I don’t agree. - Jill
[anecdote]I used to know a woman BB/powerlifter that had [Monty P] HUUUGE tracts of land [/Monty P]. She wouldn’t have a chance in the “form” competitions, but she was [Eastern Euro] strong like bull [/Eastern Euro]. She dropped a lot of body fat, but not enough to lose those breasts.[/anecdote]
The typical BB in search of form has such a low body fat percentage that the breasts are cannibalized by the body. The milk production machinery is still there, but dormant (as it is in a non-pregnant, non-nursing woman), since the ovaries don’t ovulate when the body fat %age is so low (you are obviously starving, why put your body through a pregancy?).
Not all female body builders have small breasts. Many have the best boobs money can buy.