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What's the Skinny on Body Fat Percentages for Women?

Friday, September 13, 2013

As I am entering a 60-day Paleo challenge at my CrossFit Box next week, one of the things I had to do this week was get my body fat percentage measured. Based on skin-fold caliper tests, I am at 14%. Which, according to some online sources, already puts me in the at-risk category for amenorrhea (no periods) and bone density loss.

I realized this may be an uncomfortable topic for some; I noticed right away the two men at the Max Muscle store who were measuring my body fat turned red and looked away when the topic came up. They were only able to mutter something about "all kinds of health problems" if I got below 12% before getting too uncomfortable to continue. But I found that kind of hard to believe, frankly. Whenever something comes up that is a blanket statement like that - "Women can't get below 12% body fat or they will have all kinds of health problems" - I want to investigate, because all women are different, and blanket statements about health are usually wrong (think, "eating fat will make you fat," or "eggs are bad for you," and you get the idea).

So I did a standard Google search, and lo and behold, I kept turning up that same generalized statement in various forms, with varying percentages (some said 13%, some said 10% or 15%). The two primary issues were amenorrhea - which is the cessation of menstruation for more than 3 months, for those of you needing a clear definition - and bone density loss due to an inability to absorb nutrients (fat plays an essential role in carrying nutrients through the body and allowing nutrients to be utilized).

But the reality of the issue is much more complicated than those glib, one-sentence summaries. Additional research (using Google Books, this time) turns up additional information that indicates a generic, one-size-fits-all idea of how much body fat a woman should have is not, in fact, at all accurate. Here's why:

1. A woman's natural "set-point" for body is different for everyone. Some people are naturally very lean, while others are naturally more predisposed to store fat. Also, where the fat is stored matters - there is subcutaneous fat under the skin, and visceral fat, which is stored in the abdomen around vital organs. The most common way of measuring body fat percentages (skin fold calipers) can't measure visceral fat, thus total body fat percentages can be skewed if someone has low subcutaneous fat but a higher visceral fat percentage.

I am, and always have been, naturally muscular. I add muscle quickly and relatively easily, without spending hours and hours at it. Genetically, I, and many women, have naturally lower body fat percentages. Additionally, I am not on hormonal birth control (the pill), which typically causes an increase in body fat of something like 5% to 10% (estrogen receptors are primarily in the small intestines, and synthetic estrogens are like 100x more easily bound to those receptors, so it not only causes an increase in body fat as hormone levels mimic those of pregnancy, but also interferes with the way in which foods in the intestines get processed, leading to possible higher blood sugar levels, insulin resistance, etc.).

2. The vast majority of medical studies on women with amenorrhea have been conducted on women who starved themselves to reach such low body fat percentages, or on extremely active women such as gymnasts, triathloners, and body builders. Neither of these two groups represent "average" women. Female body builders generally *do* experience amenorrhea when they go into the final stages of preparation for a show, yes. I will get back to that. And women engaged in extreme sport activity can experience similar effects. But, first to the women starving themselves - the studies done on these women showed that along with not having periods, they also exhibited bone density loss. This should be a no-brainer - starvation leads to bone loss. If fat consumption is minimal, the body will use up its own stores and then begin breaking down the bone components to pull out necessary nutrients.

However, body builders and other women who do resistance training and have very low fat percentages do not, generally, suffer bone density loss. This is because they continue to eat a healthy diet with some level of fat intake. Therefore, their bodies can use the fat from their food to carry out necessary cellular processes. So the notion that a low body fat percentage automatically equates to poor nutrient absorption and bone density loss is not accurate. If a woman is eating enough fat in her diet and is burning body fat through exercise that involves strength training, her body fat may dip below that 12% level without causing "a whole bunch of health problems".

There's this thing called the "triad" which has been the focus of a lot of studies - it is women who are involved in high-intensity sports who have a lot of pressure to not only perform well, but also look good (think gymnasts, for example). The triad involves extreme exercise and various eating disorders that lead to amenorrhea and bone density loss, as well as other health issues. Much of the research concerning a minimal body fat percentage for a healthy existence has been based on these "triad" women. But they do not, in my opinion, represent a logical foundation from which to draw conclusions regarding necessary body fat percentages for healthy women with no associated eating disorders.

3. Low body fat percentage doesn't result in amenorrhea; a rapid or sudden change in body fat percentage does. Like anything else, our bodies don't appreciate shocks to the system. A rapid change in body fat percentage - like the ones that female body builders experience when in the "cutting" phase before a competition - will likely trigger amenorrhea. Training for a triathlon or marathon can also trigger it. These are events that can be drastically stressful, and anything that is a stressor (physical OR mental) usually has some sort of physical impact. However, if a woman naturally has a low body fat set-point and reduces her percentage of fat gradually, there's no reason she can't maintain normal reproductive function, even down as low as 8 or even 6 percent body fat. This is because the ovaries manufacture estrogen/pregesterone from dietary fat, not stored body fat.

One study in the 1980s looked at a group of female distance runners; about half of the women were experiencing amenorrhea. The researchers believed they would be able to predict body fat percentages based on the women who were still having periods vs. the women who weren't. The women in the study averaged 17% body fat, and the women in BOTH groups had nearly identical body fat ranges. Some women in the group had normal periods at 18 or 23% body fat, while other women were not having a period at 18 or even 28% body fat.

My summary - it's all about the individual. If you are eating in a healthy manner and include lots of healthy fats in your diet, and if you have a naturally low body fat set point (which generally precludes anyone who is taking hormonal birth control), a gradual fat loss of a few percentage points isn't going to kill you, give you cancer or breakable bones, or interrupt your period. Rapid changes and powerful stressors may wreak havoc with your reproductive system and your long-term health, but falling below 12% body fat is unlikely to do so if the approach is gradual and you are within 7 or 8 percentage points of your natural body fat set-point.

For more information, see "The Fit or Fat Woman" by Covert Bailey, available on, or "Biology of Women" by Ethel Sloan, or "The Fragile Wisdom: An Evolutionary View on Women's Biology and Health" by Grazyna Jasienska. These books also point to the need for more studies of healthy, menstruating women with low body fat percentages; most of the studies done to date focus on women with eating disorders and the so-called "triad," and body weight as the factors of interest in amenorrhea studies.

Personally, at 14% body fat, I still have regular periods. Anywhere from 40 to 50 percent of my daily caloric intake comes from fat. I have, in the past, been much thinner and did not have regular periods at that time - but I was also experiencing heavy emotional stress,ate very little (due to the stress), and my weight loss of 7-10 pounds was rapid. I was not exercising at all, either. So, based on my own experiences, I would have to say that the rapidity of the changes, and the stress of my life at that time, was the primary cause of my amenorrhea.

After that, I maintained my low weight and began exercising again - once the emotional stress was resolved, my periods returned, even though I had not gained weight and my caloric intake increased minimally. Since then, I have gained approximately 8 pounds (some muscle, some fat). So I think for me, personally, losing 4-6 pounds should not impact my health, even if I fall below the 12% body fat cut-off point for a "healthy" woman.

Feel free to post your thoughts, comments, or experiences!
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Member Comments About This Blog Post
    Your analysis of body fat and judgements thereafter are right on, in my opinion. Thanks for doing all that research and putting it together, I read it with interest. Low body fat interfering with nutrient absorbtion is absurd to me, after all men can have body fat in the single digits with no problem. The interference with nutrient absorbtion is more related to lack of fat in the diet, not body fat percentage.
    The triads research is interesting, I read some on that, and is often related to athletes that have weight class restrictions in competitions, like rowers or wrestlers. And the dysfunction can come when they use extreme methods (like starving and dehydrating and extreme activity) to temporarily lose weight for the scale weigh-in, not when weight is gradually lost and stable.

    You have an amazing body, do be careful for sure, but if you are, you will get there and find how to stay there.
    1429 days ago
    The one thing that the trainers did mention is that not everyone can achieve those six pack abs advertised. He said that it depends on your body (again maybe he was talking about where the fat is distributed) type but some can never get it. I think they have to be somewhat generic due to everybody's body is differently made up.

    I wish you luck in achieving your goal but don't get so caught up with trying to get the "perfect" body that you can't enjoy the one you have ( that most would love to have). You still having a huge amount of your daily diet being fat may be what keeps you healthy. Keep us informed of how your progress goes and be sure to post those photos ! emoticon
    1472 days ago
    Thanks for the question on why risk it - I don't have a specific goal to lower my body fat percentage significantly, actually. I just found the blanket statement regarding the "necessary" body fat percentage troubling in it's generic-ness, and my further investigation revealed that it is actually perpetuating inaccurate health information (dare I say, even fear-mongering?) that may serve to deter some women from achieving their fitness goals. And, I tend to put up resistance when someone tells me I can't do something. Also, from my personal experience, it didn't make any sense to me.

    As far as my body, if you look at my photos, I have relatively recent ones up, and you can see/judge for yourself. I will be posting before, during, and after photos from the paleo challenge, too. I'm definitely not skinny, and I'm not interested in being skinny. I'm interested in six-pack abs. At this point in my conditioning, small numbers (1 to 4 pounds, and 2 or 3% fat percentage points) start to make a huge difference, so I do focus on them, perhaps more so than necessary.
    1473 days ago
    My question is mainly, why even risk it ? I've got a zumba instructor that has 18% body fat and has an unbelievable body (and currently getting ready to be in a muscle competition).

    I've been at 25% and LOVED the way I looked, nicely toned and fit. But not the skinny w/ bones protruding.

    I'm only concerned that you are so into the numbers that you're not truly seeing the body you currently have. You must have a great body if you have 14% and do strength training. IMO :)
    1473 days ago
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