• Isaac J. Wedig MS, CSCS

Bodyweight: What does it really tell you?

Bodyweight is a great tool for monitoring progress in your physique. It’s cheap, convenient, and for the most part, provides a fairly good measure of whether your diet and exercise program is moving you in the right direction. However, bodyweight has many limitations. The biggest limitation is that bodyweight only measures bodyweight. Let me explain.

Imagine that you decide to make a peanut butter and jelly sandwich. You take two pieces of bread, spreading peanut butter on one piece and jelly on the other. After slapping the two halves together you weigh the completed product. The sandwich weighs exactly sixteen ounces. But how much peanut butter is there? How much jelly did you use? After taking a bite out of the sandwich you decide to re-weigh it, discovering that it now weighs ten ounces. You can conclude that your bite removed six ounces of sandwich, but of that, how much was jelly? How much was peanut butter? What about bread?

Limitations of bodyweight

This is the problem with using bodyweight as your only measure of progress. A peanut butter and jelly sandwich is a bit of an oversimplification of the human body, however, the same premise applies. The body is made up of many different components, including fat, muscle, stored carbohydrates, water, and much more, just like the peanut butter and jelly sandwich is made up of bread, peanut butter, and jelly. Therefore, a change in bodyweight could be due to an alteration in the amount of any one of these components. Typically, we conceptualize changes in bodyweight as a sign of fat loss or muscle gain. And while changes in body tissues like this definitely affect bodyweight, they are not the only thing that exerts an influence on your weight. There are several components of bodyweight and a large list of variables that affect each one, making it impossible to distinguish what the exact cause of a weight change is. Just like the peanut butter and jelly sandwich example, you can’t use a measure of weight to specifically describe changes in component parts of the body.

Bodyweight can be a very useful tool in gauging whether or not your energy balance is in an appropriate place. If fat loss is your goal, then you need to be in a calorie deficit and bodyweight should be declining over time. Likewise, if muscle gain is your goal, you need to be in a calorie surplus and your bodyweight should be increasing. However, it’s very important to understand the appropriate way in which to use bodyweight in order to track this. You must know the limitations of bodyweight, analyze your data appropriately, and be sure to utilize other methods of progress tracking in addition to bodyweight. Before describing how to use bodyweight most effectively, it’s important to understand what variables can affect it. This will help you in properly interpreting your bodyweight data.

Factors that influence bodyweight

Bodyweight can fluctuate by up to 1-2% on a daily basis, which can equate to a daily change as high as 3lbs in some individuals. The small fluctuations that occur from day-to-day are not likely representative of body compositional changes, or in other words, they are not due to changes in fat or muscle content. Typically, these fluctuations are due to changes in hydration status or food bulk. Each of the variables listed below can affect how much water is held in the body and can change on a daily basis. These variables can mask changes in bodyweight that occur due to muscle and fat alterations.

1) Sodium- consuming an abnormally large amount of sodium, beyond what your body is normally accustomed to, can cause water retention and lead to an increase in scale weight. Likewise, a sudden and drastic drop in sodium intake can decrease scale weight.

2) Carbohydrates- carbohydrates are stored within both the liver and to an even greater extent, within skeletal muscle. Consuming more carbs than usual can lead to an increase in these stores, and for every gram of carbohydrate you store, you also store 3 grams of water with it. This increase in substrate and water retention in turn increases your bodyweight. Likewise, if you reduce carbohydrate intake, exercise intensely for long periods of time, or a combination, carb stores will drop and so will bodyweight.

3) Stress- both psychological stress as well as a lack of sleep can alter eating habits and have an effect on hormonal status which leads to water retention and increased scale weight. Infection, as well as muscle damage occurring in response to training, also forms of stress, can lead to inflammation and fluid retention as well. Going from a high stress state to a lower stress state can cause a decrease in bodyweight.

4) Menstruation- hormonal shifts during certain phases of the menstrual cycle can cause changes in fluid retention. Men, this is not a problem for you.

5) Alcohol- alcohol is a diuretic and can cause dehydration, a loss of body fluids, and thus a decrease in bodyweight, as long as calories are controlled. Alcohol consumption also tends to increase hunger and promotes the consumption of excess calories, which in turn may potentially increase weight.

6) Food Bulk and Digestion- eating higher volume, higher fiber foods, and more ‘food bulk’ than usual can lead to weight increases simply as a byproduct of excess food sitting within your digestive system. Changes in your digestion rate or a deviation from the regularity of your bowel movements may affect bodyweight as well. Less regular movements or constipation can increase bodyweight, while diarrhea or more frequent bowel movements can decrease weight.

7) Drug use- antidepressants, anti-inflammatory and anabolic steroids, including birth control, and a number of other prescription drugs can alter fluid balance.

As you can see, bodyweight is affected by much more than just fat and muscle amounts. When it comes to your physique goals, if all your measuring with bodyweight is fluctuations in water and food bulk, then what good is it? A good quality measure has to have validity. In other words, it has to measure what you’re actually trying to measure. For physique goals, the primary thing that you’re interested in measuring is body composition, the relative amounts of body fat and muscle mass, not hydration status. Bodyweight alone is not a very valid measure when it comes to assessing body composition. Bodyweight is not the most valid measure for physique goals, it can be misleading, frustrating, and quite limited. However, when used appropriately, it still has merit.

How to use bodyweight effectively

If you wish to use bodyweight as a measure of progress, which I do recommend to most individuals, you have to be sure to do three things; 1) take consistent measures, 2) compare weekly averages, and 3) use it in conjunction with other measures.

1) Take consistent measures

Consistency of your weigh-ins is very important. This means taking your weight at the same time of day, in the same clothes, and in the same fed/hydration state each time you weigh-in. The best way to ensure consistent weigh-ins is to record your bodyweight every morning upon waking, after using the bathroom, before consuming any food or beverage, and preferably in the nude. Try to use a digital weight scale as they are more accurate and consistent than a spring mechanism.

2) Compare weekly averages

You aren’t interested in measuring and comparing day-to-day changes in bodyweight that come from fluctuations in hydration status or food bulk. By taking weekly averages, you can smooth out the small variations in bodyweight that occur on a daily basis, highlighting only average changes that occur on a week-to-week basis, which are more likely to be representative of changes in body tissue rather than hydration status. Try to collect good consistent bodyweights as many days of the week as you can. The more days that you collect, the better you averages will represent the week. In order to use bodyweight as a decent proxy of energy balance and tissue change, compare your averages from week-to-week. If your average bodyweight trends appear to match up to your desired goal, then you’re on the right track. If fat loss is your goal, weekly averages should be declining. If muscle gain is your goal, then weekly averages should be increasing. If this isn’t the case, your training and nutrition may need some tweaking.

3) Use in conjunction with other measures

When measuring your progress on a diet and exercise program, its important not to put all your eggs in one basket. Generally, the more measures that you use, the better. It’s a bad idea to relying exclusively upon one measure to guide your journey, especially when it comes to physique goals. Remember back to that delicious peanut butter and jelly sandwich, weight wasn’t a great measure alone because it didn’t tell us anything about how much peanut butter or how much jelly we used. Likewise, with a physique goal, we’re not just interested in weight, we want to measure relative changes in body fat and muscle. Therefore, in addition to bodyweight, we need to utilize methods that can help to specifically detect changes in fat and muscle amounts. These include physique pictures, body circumference measures, skinfolds, body composition tests, and gym performance. Although all of these measures carry their own inherent limitations, when taken collectively together, they provide a much more comprehensive report of your progress. These alternative measures can help to detect changes in body composition that might have otherwise gone unnoticed by monitoring bodyweight alone. For example, say that your bodyweight remained unchanged yet your waist circumference and belly fat skinfold measures deceased. You clearly had losses in body fat around your midsection but they were masked by increases in bodyweight that might have come from extra water retention. Had you measured bodyweight alone, you would have missed your progress, gotten frustrated, and possibly abandoned ship on your diet.

For most individuals I recommend using bodyweight in combination with physique pictures, body circumferences, and perhaps even skinfolds. These are the most convenient, inexpensive, and practical measures to use. As a note on skinfolds, the best way to utilize them is to compare relative skinfold thicknesses from specific sites over time, rather than using them to calculate and compare relative body fat percentages. An additional measure, which can be great for tracking changes in muscle mass, is gym performance. If you are able to lift 10lbs more this month than you could last month, for the same number of repetitions, that’s a decent indication that muscle growth has occurred. Likewise, if performance has dropped, it may indicate muscle losses. Again, as with the other measures, there are limitations and certain assumptions with correlating muscle mass to performance, however, it serves as one more tool and some additional data to consider. The more you measure, the more you can manipulate. If you don’t track your progress at all, then you’re left in the dark and have no way to tell if you’re on course towards your goal.


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