I recently read a book about this, and must say, I learned a lot even though I work and write in the diet and fitness industry on a daily basis.
I always thought a man could only have this problem if he was overweight and his body contained lots of extra fat, and the men I'd seen with man boobs seemed to bear this out. Seemingly to me, the body just stored the fat in an unlikely place.
The first thing I learned from the book was all about how testosterone works. In teenagers, hormones are all out of whack, and in normal men, testosterone hits its peak in the early 20's. (We all know that wild period in a man's life, don't we?) It's those high testosterone rates that cause them to get the deep voice, chest hair, and yes, a nice flat, manly chest. This is why most doctors tell young men and teens that they will outgrow their man boobs - the body naturally takes care of it in most men.
I also learned from that if the testosterone doesn't peak high enough, or if it peaks, but drops too quickly, it can cause feminine traits, like baby smooth skin on their chest, not much facial hair or changes in voice, and yes, even man boobs.
Apparently, there are ways for doctors to combat this by changing the hormones in grown men so that they have the right balance that the body requires to function properly as it was designed to do. This proper hormonal balance is what is necessary, even before any diet or exercise will begin to help with this embarrassing problem.
