Let me start off by saying that I have no medical training whatsoever, so feel free to disagree with me or correct my thinking.
I find it difficult to believe that a properly nourished human female would have difficulty conceiving, no matter her bodyfat content. I do believe that different people have different levels of bodyfat that are right for them.
I don't know what studies are being referred to when declaring that low bodyfat is related to difficulty conceiving. Are the women in the study properly nourished? What is the amount of bodyfat that is supposedly required? Perhaps there is another factor involved here. After all, I have never heard of a chimpanzee or gorilla not being able to conceive because they only ate raw food.
To use myself as an exmple:
Before I had my first child, I weighed 108 pounds (I am 5'3''). It took me 5 1/2 months to conceive. According to my doctor, the average for a healthy woman is 4 months. Before I had my second child, I weighed 96 pounds. It took me less than 1 week to conceive. (My husband is in the military and I got pregnant just after he returned from a 7-month deployment). The only time I have ever had my bodyfat checked was about 1 year before my first child, before I started a weight training program. I weighed just short of 110 pounds and my bodyfat was less than 16%. Thus, my bodyfat at the times of conceiving my children must have been less than this number, (if the number was accurate).
Also, I am currently living in Japan, where I assure you that at least 25% of the women I see with small babies are under 100 pounds and probably have no more bodyfat than I did when I conceived. Japanese people eat much healthier than the average american.
Also let me add that I have begun to eat a mostly raw diet. I have lost 3 inches on my waist, but my weight is still 96 pounds (my legs are stronger since I walk more now). My period used to come every 5-6 weeks, but now it is, unfortunately, every 4 weeks. I know my body is still indetox, so I am thinking that my period is necessary to get rid of some of these toxins. My cramps are significantly less now, so hopefully my period will get lighter and I hope disappear altogether someday.