Your weight on the scale can be misleading

There seem to be electronic gadgets that allow us to monitor just about every aspect of our body’s functions. From sleep quality and heart rates, to blood oxygen and blood glucose levels, to calorie intake and energy production, we no longer have to rely on visits to the doctor to monitor our state of health. And we can follow up daily.

But it seems that the health device industry has overlooked an essential monitoring tool: one that will measure the percentage of fat, muscle and water in our body that determines our weight.

Given the national obsession with whether we’re overweight or obese, it’s curious that the only device most of us have to determine this is our scale. (Or try on the clothes we wear when we think we’ve gained weight.) Of course, scales are reliable measures of changes in our weight and will tell us what we weigh today, but can we always translate the weight on the scale as normal, overweight or obese?

A standard for normal or obese status is BMI, body mass index. There are graphs in which the BMI can be plugged in to see if our weight is in the normal or abnormal range (too low as well as too high). BMI is determined by dividing your weight in pounds by your height in inches squared, then multiplying that number by 703. The charts give the normal, overweight, and obese range for men and women.

But there are obvious problems with relying solely on the scale, and subsequently BMI, to assess “fat or thin.” Since BMI relates weight to height, decreasing height, as many do in old age, can cause a person to go from normal to overweight or obese. A medically approved weight for someone 5’10” may be overweight if the individual is now 5’7″. (I have a cartoon that shows a woman on stilts standing on a scale, and since she’s now 5 inches taller, she figures her BMI is normal.)

Muscle weight can also confuse BMI accuracy. The scale does not differentiate between the weight of muscle, fat or water. Two people can weigh the same but have different body compositions; we are very muscular and we have too many fat cells. A male friend found himself losing weight when his prostate cancer treatment depleted his body of testosterone. Much of the weight loss was due to muscle loss, a side effect of his treatment.

Methods that assess body composition, however, are not readily available to non-professionals, with the exception of skin calipers, and even they require the expertise of someone trained to use them. The skin is pinched with calipers at several places on the body and the thickness (which represents subcutaneous fat) is analyzed in a mathematical formula. A do-it-yourself skin thickness measurement is possible, but only after a lot of practice and supervision by someone who knows what to do.

The scales are available with an additional body composition measuring device that uses bioelectrical impedance. You stand or grab electrodes, and tiny electrical impulses are sent through your body. Lean tissue conducts impulses faster than fat tissue, so impulses travel faster when the individual is leaner. Again, there are formulas to translate the numbers into relative amounts of fat and lean tissue.

But here too the measurement can be inaccurate. Hydration affects the reading because water conducts electrical impulses, so drinking water or sweating before measurement will alter the results. Eating before measurements also affects measurement, as does exercise.

If you have access to a swimming pool, hydrostatic weighing could be an option. After exhaling as much air as possible, you sit underwater and your weight is recorded while fully submerged. It is then compared to your weight on earth. Both weights, with the appropriate mathematical manipulations, reveal body density, which in turn provides information about the components of the body that contribute to body density. Its only downside (other than not enjoying holding your breath and sitting underwater) is that the method measures bone density, and bone density which can be changed by exercise or bone loss will affect the measurement accuracy. In addition, this method is unlikely to be used frequently to track the effects of, for example, dieting.

Dual-energy X-ray absorptiometry, otherwise known as DEXA, is probably the most accurate method of determining body fat content, but it’s not something you can do at home. You have to go to a special facility and lie on a table while the arm of the machine passes over your body emitting high and low energy X-ray beams. The beams are absorbed by the various components of the body and are translated into readings for bone, lean body mass and fat density.

The machine can give surprising results. Years ago, when we were studying the eating habits of thin women going through the first weeks of smoking cessation, we, with their permission, examined their body mass using DEXA. To our surprise, the amount of fat in their body was somewhat similar to that of an overweight or even obese person. The scale recorded a low weight because their muscle mass was low, not because they had only small amounts of fat in their body.

DEXA measurements require an appointment at a clinic and justification from the health insurer for the measurement. Right now the backlog of appointments due to COVID means waiting for clearance and appointment. Obviously, this is not an easily accessible method for determining body composition changes related to weight loss or gain.

So the question remains, where is the new technology to allow us to take accurate measurements of our body composition at home? We should be able to tell if our weight loss program is maintaining our muscle mass or if we are losing weight because we are losing muscle in addition to fat. We should be able to know if the treatment we are taking for bone loss is stopping the loss and increasing bone density. We need to know if our elderly family member is unable to get up from a chair or walk unaided due to muscle loss. We need to know if our older teenager’s weight is increasing because he is engaged in a vigorous exercise program or because he eats fast food every day after school.

Given the rapidity with which medical devices for home care are being developed, it is hoped that an easy-to-use and accurate device will be available in the near future. Being able to accurately and often track our own changes in body composition will have benefits beyond knowing how quickly our fat mass is changing.

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