I cannot relate to amenhorrhea, as I have not experienced this. I have heard of raw foodists who say that even though they do not have a period, they know that they do ovulate. Supposedly if the blood is healthy and the body is healthy, a woman's body can reabsorb and use the blood and therefore not need to shed it? I don't know.
I was speaking to your statement -
"women who don't have enough bodyfat have menstrual irregularities and difficulty conceiving". This sounds like a definitive statement to me, though I do not know the definition of "enough".
You hear this all the time in the USA. I was just wondering the truth to the low bodyfat thing, as I seem to have experienced the opposite. The healthier I eat, the less my bodyfat seems to be and the more regular my period has become. I do not know my exact bodyfat percentage, but I can safely say that at 5'3'' and 96 pounds, it is pretty low, yet I am menstruating regularly.
I do not believe the general statement that low bodyfat is the cause of irregularity and conception problems. I believe that if someone is low bodyfat due to malnourishment, then they may have problems in those areas. But I think that americans in general are malnourished, resulting in fertility problems regardless of bodyfat percentage. Isn't it true that obese women also suffer from menstrual irregularities and difficulty conceiving?
In any scientific study, correlation doesn't always equate to cause and effect.
The study you site says:
"Since many raw food dieters exhibited underweight and amenorrhea, a very strict raw food diet cannot be recommended on a long-term basis."
Underweight is a relative term. Though I am considered to be underweight in the USA, I am of normal weight here in Japan. In fact, if you took one of over 50% of the women of childbearing age from this country and told the National Inquirer that they were a movie star, you would probably see an article printed up about them wondering if they were anorexic or what other eating disorder they had. Though I am fairly confident that these "skinny" women are, in general, much healthier than their "healthy amount of bodyfat" american counterparts.
Again, one would have a difficult time convincing me that a chimpanzee or gorilla would be healthier and/or more fertile if they would give up their raw food diet.
It does not seem as though this study showed if ovulation was still occuring in the women, just that they had amenorrea. "Many" women exhibited this? Did they compare it to the general public to see if incidences of amenorrea were higher there?
Also, the fact that someone is on a raw food diet does not mean that they are properly nourished. There is a right way and a wrong way for every way of eating. I could eat nothing but nuts and seeds all day long and consider myself a raw foodist and still be malnourished.
In summary, in my totally uneducated, coming from experience opinion, I believe that you can have very low bodyfat and be fertile, as long as you are not malnourished.