Debate with my girlfriend: Female runner body fat % in relation to menstrual cycle

Is your girlfriend fat?

No, she's an aerobics instructor who's in great shape and eats right.

Females with extremely low body fat will stop menstrating due to what you are calling a "safety mechanism".

2% body fat is too low. There are several health problems related to body fat below 4%. Anything below 3% should send up a major red flag.

I would seriously doubt that Shorter and company actually had 2% body fat. I would be willing to bet that is a slight exageration of a 3.8 to 4%.

When a female athlete with low body fat starts missing periods, it is usually because her body is in survival mode and has shut down menstruation just to survive, and to conserve energy. So in that way, it is what you would call a "safety mechanism". Her body is dealing with too low body fat and maybe starvation, and so it shuts down the ability to menstruate and thereby procreate because these things are expendable compared to basic survival. And while it doesn't seem like that big of a deal, if a woman goes without menstruation for several years, she could deal with extreme bone thinning from a lack of estrogen (which happens when your body shuts down menstruation) and even develop osteoporosis.

it's not a body fat issue. The reason the cycle stops is because there is not sufficient fuel to develop a fetus. The only fuel that a fetus uses from its mother are Carbohydrates. The cycle becomes suspended because there are not adequate CHO reserves (either through high levels of activity or malnutrition). Once CHO levels return, the cycle begins again.

Women with below 15% have had regular cycles, and women as high as 23% have not. For further accreditation, I'll try to get a hold of my favorite exrcise physiologist who did her master's work on this topic.

Failure to have a period IS a bodily safety mechanism. If the body is not getting enough calories, the first thing it shuts down is the fertility system. It is very possible for a women who is eating enough (meeting her energy needs) to have a low body fat % (<13%) AND maintain her period. I hover @ 12-13% (have been as low 11%) and have a regular period. I am sure most elite female distance runners are <12% and are having regular periods. If not, they would be having stress fractures regularly and would not be elite athletes. And how many of them have become mother's?? Now, I am not sure how Marion pulled that one off in between the drugs but that is another topic for another thread.

25% for a man....VERY fat!! 2%...hard to believe.

ONON

SP wrote:

2%...hard to believe.

ONON

Had mine measured once by a doctor at 2.2%. It is possible. I will note that I wasnt really "healthy" soon after that and got hurt. 3% in a runner isnt hard to believe at all.

How did the "doctor" measure you? I have no doubt you are a skinny bastard but I strongly suspect he was off at 2%. About 4% is what the average elite Kenyan male is lugging around.

trackhead wrote:

it's not a body fat issue. The reason the cycle stops is because there is not sufficient fuel to develop a fetus. The only fuel that a fetus uses from its mother are Carbohydrates. The cycle becomes suspended because there are not adequate CHO reserves (either through high levels of activity or malnutrition). Once CHO levels return, the cycle begins again.

Women with below 15% have had regular cycles, and women as high as 23% have not. For further accreditation, I'll try to get a hold of my favorite exrcise physiologist who did her master's work on this topic.

IT HAS NOTHING TO DUE WITH A FETUS. SHE IS NOT PREGNANT! IF SO THE CYCLE WOULD OBVIOUSLY STOP. THE STOPAGE DOES HAVE A RELATIONSHIP WITH THE ENERGY SYSTEM, BUT NOT A FETUS!

SP wrote:

I hover @ 12-13% (have been as low 11%) and have a regular period.

25% for a man....VERY fat!!

If you believe 11% is not unhealthy for you, then wouldn't you believe 25% not unhealthy for some men?

What is the only fuel source used during pregnancy for a developing fetus? If that fuel is not there is appropriate quanitities, the cycle will go dormant.

1_Coach wrote:

IT HAS NOTHING TO DUE WITH A FETUS. SHE IS NOT PREGNANT! IF SO THE CYCLE WOULD OBVIOUSLY STOP. THE STOPAGE DOES HAVE A RELATIONSHIP WITH THE ENERGY SYSTEM, BUT NOT A FETUS!

Trackhead wasn't saying that a fetus was present. The issue is that if the body does not have enough evergy to support a fetus IF ONE SHOULD BE PRESENT IN THE NEAR FUTURE, then it will prevent a fetus from being made. now stop yelling.

It is most likely related to body fat, but other factors can likely shut down the reporductive cycle. The key is the hormone leptin which is secreted by fat cells. When leptin levels drop too low (due to feduced fat cell size) reproductive function shuts down. This was shown first in rats and mice with a genetic mutation causing them to be unable to produce leptin. They get incredibly fat becuase they eat constantly; the absence of leptin, which the brain interprets as a sign that the organism is starving, is a powerful stimulant to eat even when already fat. Reproductive function is also shut down in these animals, even though there is way more than enough fat, becuase the brain is led to believe the animal does not have enough fat due to the absence of the leptin hormone. Treating the animals with leptin will cause the reproductive function to return.

Of course, humans aren't mice, and female distance runners aren't completely lacking in leptin like these mice, but the lesson is that the body has a system in place to shut down reproductive function when fat stores are too low.

However, there are a lot of factors that determine whether an individual female will become amenorrheac beyond total body fat.

are you stupid? wrote:

1_Coach wrote:

IT HAS NOTHING TO DUE WITH A FETUS. SHE IS NOT PREGNANT! IF SO THE CYCLE WOULD OBVIOUSLY STOP. THE STOPAGE DOES HAVE A RELATIONSHIP WITH THE ENERGY SYSTEM, BUT NOT A FETUS!

Trackhead wasn't saying that a fetus was present. The issue is that if the body does not have enough evergy to support a fetus IF ONE SHOULD BE PRESENT IN THE NEAR FUTURE, then it will prevent a fetus from being made. now stop yelling.

Hey look, I'm not yelling, but I know what I'm talking about. You and trackhead are incorrect. I do not have time to spell out the entire physiology, but you are wrong. There is more than carbs that go to a fetus. You don't have to believe me and I figure you probably won't, but I encourage you to read some books on the matter.

By the way, I did not mean to yell, but merely trying to create a distintion between the quote and my post. I am sorry if you were offended.

So, 11% is essential for a woman, so what is wrong with that?? Like I said, I am not that low right now but when I set my PR's, I was 11.5% @ Cooper Clinic under water. Wish, I was that now as myabe the race times would be better.

OK, so I will buy that some men test 2% as that is what is "essential."

But, I still say men @ 25% is pretty fat!! I was 25% in college and was not heavy but for sure fat.

ONON

The carbohydrate argument used here is just wrong. Highly trained women are not likely to have inadequate carbohydrate reserves, unless their training is also accompanied by some sort of eating disorder. If the low carb theory was right very few endurance runners would stop menstruating, but every fat-ass following the Adkins diet would be infertile. Do you see that going on?

Where are your CHO reserves at the end of a 2.5hr run? Or after 40min of hard running? They are not dependable reserves. They are constantly being replenished, yes, but reserves are always being tapped.

From my Exercise Physiology text (by Powers and Howley p. 426-427):

What causes menstrual cycle dysfunction in athletes? The current belief is that the cause may vary between individual athletes and is probably due to multiple factors. Although some studies linked a low percentage of body fat with athletic amenorrhea (41), recent evidence does not fully support the notion that low body fat is the principal cause of amenorrhea (27, 58).... As the weekly training distance increases, the incidence of athletic amenorrhea increases in proportion to the increase in training stress.... Exercise alters blood concentrations of numerous hormones, which may result in a modification of of feedback to the hypothalamus. This, in turn, may influence the release of female reproductive hormones and therefore modify the menstrual cycle.... high mileage may result in increased psychological stress. Psychological stress may disrupt the menstrual cycle by increasing catecholamines or endogenous opiates, which play a role in regulating the reporductive system (41)."

The point is there are NUMEROUS factors that could affect the menstrual cycle. Even if you were to find something that supports your view, there is something out there to counteract it. Regarding body fat % for males verses females, according to my textbook, male distance runners average between 3.7-18.0% BF, while females average between 15.2-19.2% BF. 15% for a male is not "very fat."

Basic, but nicely done. I believe my statements have supported everything you have said.