Womans Body Composition

Having examined the normal menstrual cycle and the most common hormonal modifiers, I want to discuss the topic of body composition for the next several blogs. There are two primary reasons I want to do this. The first is that the differences in body composition between women and men tend to underlie many of the differences that are seen in terms of apparent gender differences in fat gain, fat loss and exercise performance. Hormonal differences (and the changes that occur) clearly play a role but the difference in body composition tends to explain a great deal of the differences that are seen.

The second has to do with a topic that will take up a large portion of the blogs ahead, which relates to dieting and what I will for now call weight loss. I mentioned that women are generally more likely to be dieting than men and this is true whether the general population or an athletic population is being examined. There are still many long-held misconceptions and simply poor ideas about dieting and many of them relate to a misunderstanding of the differences between body weight, body fat and body composition.

Because while many who pursue dieting tend to still think in terms of weight loss itself, looking at body composition is not only far more accurate but far more important. This isn't to say that the scale doesn't have it's uses or that weight is irrelevant in all situations. But there are a number of potential problems with it by itself. To nobody's surprise, there are a set of issues that women face in this regard that men really don't. Understanding body composition, what it means, along with the differences between body weight and body fat, are a key aspect of improving women's results in everything from dieting in general to improving their athletic performance.

Body Composition


So what is a woman's body actually made of? The answer is a whole bunch of different things including bones, skeletal muscle, organs (heart, liver, kidney, brain, etc.), water, stored carbohydrate, blood, minerals and of course there is body fat. For simplicity's sake, these different components of the human body are typically divided into two categories. The first is fat and includes, well, all of the different types of fat that I will discuss in some detail below. Everything that is not fat will be called lean body mass (LBM) and you'll sometimes see this called Fat Free Mass (FFM). For all practical purposes they are interchangeable and I will use LBM throughout these blogs.

What is LBM and What is it For?

While many, especially in the athletic community, tend to equate LBM with muscle, this isn't really accurate. Rather, LBM refers to everything that isn't fat and this includes a number of distinct tissues which are structurally very different. The brain has a very specific structure as do the various organs (including a woman's reproductive organs). Bone is it's own tissue as is skeletal muscle. Water, minerals and carbohydrates are all distinct as well. Every type of LBM in the body tends to have a fairly specialized purpose. The heart pumps blood, kidneys filter waste, the liver is involved in tons of different biological processes, bones provide the body with a physical framework, skeletal muscle generates force for movement, reproductive organs exist for reproduction, etc. All are important although, as you'll see later, some are relatively more important than others in terms of short-term survival. They are all important but as I'll talk about below, only a few are really that relevant in terms of what can or cannot be impacted on by diet (or training) and what is really worth paying attention to in the short term.

While the amount of bone, or rather how dense bones are, is critical to women's health, the primary type of LBM that is important in terms of altering body composition is skeletal muscle. Other types of LBM can change, water and glycogen for example, but changes in the amount of muscle are key here. Skeletal muscle is made up of a number of different types of tissue. The actual muscle fibers are made of protein but this is only about 25% of the total in muscle. The rest is a combination of water, minerals, stored carbohydrate (called glycogen), intramuscular triglyceride (IMTG, fat stored within the muscle itself) and the various cellular machinery involved in muscular metabolism.


What is Body Fat and What is it For?

In contrast to LBM