Although it has been changing in the last decade or so, the reality is that most people (women or men) tend to focus only on changes in body weight. If weight goes up, that's usually bad (unless it is an athlete trying to gain muscle) and if weight goes down that's usually good. For the sake of example, let's say someone starts a diet and a few days later their scale weight has dropped by a few pounds. Most would consider that a success but I would ask the following question: What was lost? Was it water, stored carbohydrate, muscle, fat, bone, organs?
Perhaps the person just had a big bowel movement.
The scale can't answer this question in any meaningful fashion and this presents a rather large problem. And this becomes an enormous practical problem as many people, especially if they are dieting, not only focus solely on the scale to track their progress but often obsess over the changes (or lack thereof). They may weigh multiple times per day (or before and after going to the bathroom) and often over react completely to small day-to-day changes in body weight. A frequent pattern is that if weight goes down, that means it's time for celebration. Bring on the cake. But if weight goes up, it's time to reduce food intake even more and add an extra hour of exercise to the gym. As you'll see below, these types of short- term changes are relatively meaningless overall although daily weighing can still be useful so long as it is approached correctly.
Women, primarily the normally cycling female but also others, have an added problem here that I will discuss below.
The only bodily tissues worth worrying about when it comes to the above are water, the carbohydrate stored within muscle (which is actually related to water storage), digesting food, fat mass, and the part of total LBM that is represented by muscle.
Food residue, the undigested food moving from the gut through the colon before excretion can actually make up 3-7 lbs (~1.5-3 kg) depending on the diet (high-fiber diets tend to produce more food residue) and this can be a significant portion of a woman's total bodyweight in some cases. But over most realistic time frames (i.e. the months that most diets will last), those are really the only tissues that need to be worried about. And the basic bathroom scale can't differentiate between them.
That said, there are some general comments that can be made regarding the relative contribution that changes in food, water, carbohydrate, muscle and body fat may be making changes in body weight and over what time frame.
Almost without exception, very short-term changes in scale weight tend to represent changes in water, glycogen or food residue (a good bowel movement can cause a 1-2 pound weight loss in some cases). Even small changes in the diet can cause scale weight to change pretty significantly in a fairly quick period of time. Someone on a low-sodium diet who eats high-sodium meal may bloat up for a day or two, gaining several pounds of water weight. Chronic stress can also cause water retention due to the increase in cortisol which binds to the receptor involved in water retention.
Dietary carbohydrate intake can enormously impact on water weight. Through a variety of mechanisms, when carbohydrates are lowered, the body tends to lose a lot of water; losses of 1-15 pounds in a few days have been seen in studies of low-carbohydrate diets. Many diet books use this to their advantage. By lowering or eliminating carbohydrates from the diet, body weight drops enormously in a few days and this can be very rewarding to the dieter. It can also backfire when dieters get frustrated that the rapid losses don't continue indefinitely. They may lose 5 pounds in the first week due to water loss and then lose "only" 1-2 pounds per week after that.
This works in the opposite direction as well: someone who has been on a low- or even lowered- carbohydrate diet who eats a lot of carbs for one reason or another can see their weight spike fairly significantly (large individuals may gain 7-10 pounds in one or two days). Every gram of carbohydrate stores 3-4 grams of water with it which explains the big increase in body weight. This partially explains why women often "feel bulky" when they start weight training. Their muscles start storing more carbohydrate and this causes them to store more water. But it goes away within about a week.
While all of the above is true for both women and men but normally cycling women have the added issue of the menstrual cycle (recall that some forms of birth control can cause water retention and PCOS women may experience issues at nearly random times). Most women are familiar with how wildly their body weight may change throughout the month. I discussed the hormonal reasons why in in the blogs before, but the late follicular and late luteal phase tend to be the worst and body weight changes of 5-10 lbs (~2.5-5 kg) are not unheard of. This tends to generally drive women crazy (even women well versed with body composition can be affected psychologically by this) but it gives women an additional factor in tracking changes that men don't have.
And it's absolutely critical for people to realise that all of these changes, small or large, don't represent anything meaningful in terms of reaching their goals. Rather, given the actual rate of change in levels of body fat and muscle mass, these rapid changes can only represent the gain or loss of water, carbohydrate, food in the gut, etc. As I will discuss in a later blogs, storing a pound of actual body fat takes about 3,500 calories over maintenance which makes a true loss or gain of 4 pounds of fat a physiological impossibility as it represents 14,000 calories of energy. To eat that many excess calories or burn that many calories through exercise in one day would be impossible.
The above should not be taken to mean that body weight is meaningless or that the scale is useless. Rather, it must be understood that short-term changes in bodyweight don't represent anything meaningful in terms of what people are trying to lose (or gain). As well, the scale can still have its place to track progress, it must simply be used appropriately.
Fat and Muscle
As short-term changes in body weight always represent water, glycogen, etc. they don't particularly count in terms of actually changing body composition. Certainly it may change a little bit with water or glycogen loss (both of which count as LBM), but overall changing the ratios of body fat and skeletal muscle is how body composition changes. When trying to lose (or gain) weight, individuals should really be focused on the changes in either fat or skeletal muscle that are occurring. Fat loss will be best achieved by losing fat while either maintaining, or even slightly increasing, the amounts of muscle while muscle gain should ideally come with as little body fat gain as possible (it's usually impossible to avoid it completely).
I'd note that the scale still can't differentiate changes in fat and muscle either, they do occur over a much larger time scale than changes in water, glycogen or food residue. So while a 2-3 lbs (~1-1.5 kg) change in body weight over a day will assuredly represent nothing more than water weight or food in the gut, that same change over multiple weeks is far more likely to represent a "real" change in body composition. Even that conclusion can be problematic depending on when body weight is actually measured. If someone only measures once per week (i.e. on Monday) the change from the first to the second measurement might represent a real change or might not.
Short-term changes in body weight don't represent anything real while longer term changes generally do. The short-term changes can only be water weight, etc. while the long term changes are far more likely to represent real changes in the amount of fat or muscle someone is carrying. That said, when females want to improve their appearance, health, etc. the goal should not only be to lose (or gain) weight. Rather it should be to improve their body composition, to lose fat, gain muscle or some combination of the two.
Body Fat Percentage
While the overall concept of body composition has to do with the fact that the human body is made up of different amounts of different tissues, since we are dividing the body into only LBM and fat mass, it's more useful to think in terms of body fat percentage (BF%). This represents the percentage of someone's total weight that is made up by fat (by definition everything else is LBM). If someone has a BF% of 30%, the other 70% is LBM. If their BF% is 20%, they have 80% LBM. I'll present some representative numbers later but this percentage can range from a lower limit of 10-12% in the leanest women up to 50- 60% in cases of extreme obesity.
And while body composition in the most general sense is more associated with appearance and health than weight per se, BF% is arguably even more related to both. A woman at 25% body fat will not only have a different appearance but is likely to be healthier than one at 45% body fat I'd mention again that the distribution of body fat is also relevant here and a more typical female fat patterning (gynoid or pear shaped with body fat in the lower body) is metabolically healthier than the typical male fat patterning (android or apple shaped). In this vein I'd note that, even more than body weight per se, body composition is far more related to overall health. If someone loses fat and gains some amount of muscle, their health will improve even if their body weight per se is unchanged.
Within the context of this blog, perhaps the larger attention to be more worried about BF% and body composition is that it will be a much larger determinant of appearance than just body weight. Two women at the same weight with a different BF%/body composition may look totally different. So consider two women who both weigh 130 pounds. The first is an athlete at a relatively lean 18% body fat while the second is inactive with 28% body fat. Their weight is the same but their body composition is different and the athlete will be visibly more muscular and leaner than the inactive woman.
And while body weight can change due to shifts in water weight or food residue without any real changes in BF%/body composition occurring, it's entirely possible for body weight to stay the same while body composition is improving. So consider a beginning exerciser who gains 2 lbs of muscle while losing 2 lbs of fat. Her weight will be unchanged although her body composition will have improved. Or consider a more extreme example where a woman starts at 130 lbs and 25% body fat and 6 months later she is 130 lbs at 20% body fat. She may look completely different while weighing the same.
Related to this, the predicted weight loss (or gain) may be lower than expected due to changes in body composition. If a woman gains 2 pounds of muscle while losing 4 pounds of fat, she will have only lost 2 pounds on the scale although her fat loss is double that. Her weight will only go down by two pounds but the impact on her body composition, health, appearance and how her clothes fit may change significantly.
Finally, this can work in the opposite direction. If body fat is gained while muscle is being lost, BF% may increase and body composition worsen despite no change in weight. I mentioned an example in a previous blog when I discussed how some forms of hormonal birth control can cause a slight loss of muscle and gain in fat despite no real weight change.
The same occurs at menopause without hormone replacement therapy, even if a woman's body weight doesn't change much, she will start to lose LBM while gaining fat (along with a shift in fat distribution). Weight is unchanged but body composition is worsening.
In the next blog we will look at measuring and tracking body composition
The above information is taken from the The Woman's Book by Lyle Mcdonald with Eric Elms.