There is recent debate about women and the safety of fasting.
It IS TRUE that many women have had problems when they added fasting into their diet and nutrition plan. But, the question becomes, was the problem the fasting?
It should come as no surprise that there are obvious gender differences in how the human body works. From the way genders look to their unique metabolisms, men and women do have very different physiologies. In fact, there are entire books dedicated to the topic (my favorite being “Gender Differences in Metabolism” by Dr. Mark Tarnopolsky).
In short, aside from the obvious physical differences in muscle mass and body fat levels, women also differ from men due to women having their own set of unique metabolic and physiologic needs that relate to their child-bearing physiology, and this fact simply can not be ignored when discussing diet and weight loss.
A woman’s ovarian function is particularly sensitive to energy balance and energy flux, which can be explained easily by saying a woman’s body is constantly monitoring the energy available since the energy needs for pregnancy are high. If the energy needed to support pregnancy is not available, or is perceived to be at risk of becoming unavailable, then the body takes steps to lessen the chance of pregnancy.
In fact, “available energy” is monitored in three distinct ways:
1) Energy Status – The amount of stored energy within a woman’s body. This is most often thought of as body fat or body fat percentage.
2) Energy Balance – The balance between calories in and calories out. Basically whether or not a woman is actively losing weight.
3) Energy Flux – The RATE of calories in and the RATE of calories out. A woman may not be losing weight, but her calorie intake and output are extremely low, or both extremely high.
As an example, a woman with very low levels of body fat (15-20%) may be at higher risk for metabolic changes due to her low amount of available energy, since the amount of energy stored in her body fat may not be enough to support a full pregnancy.
A woman undergoing prolonged severe dieting may be at higher risk for metabolic changes because of the large discrepancy between calories in and calories out, despite still having higher than average levels of body fat.
And finally, a woman who is not losing weight — or is calorie balanced — but the flux is extremely high (athletes who eat and burn 3,000+ calories in a given day) could be at risk of metabolic changes because of the high flux of calories, even though she is in calorie balance and has normal levels of body fat.
So a woman who wants to lose weight must be aware that her unique situation will affect how her body responds to any particular weight loss or exercise program. And this includes fasting. A woman’s current body fat level, her exercise program, and her degree of dieting are all risk factors.
Sadly, this is well-known physiology. Physiologic and metabolic disturbances like the female athlete triad have been studied for years. So people who are saying that fasting CAUSES issues with women’s hormones, without looking at the other possible factors either don’t understand this physiology, or are ignoring it. Both are equally concerning.
Either way, fasting itself I don’t see as the issue, but something that exasperates any one of these three issues.