by Wallace C. Donoghue

In recent years, the measurement of percent body fat has become widely used and recommended as one of the indicators of fitness. By monitoring percent body fat and weight regularly, there are many things a person can learn about their fitness and any changes in fitness as time progresses, that cannot be learned by simply weighing with a scale. Later in this section I will tell you how to measure percent body fat, but first I will explain it and tell about the many benefits obtained by monitoring body fat.

Benefits of Monitoring Body Fat

Perhaps the most important single thing the monitoring of percent body fat will do is determine changes in muscle tissue over time. By knowing percent body fat, the percent of muscle, bone, organs, etc. can also be determined. For example, if a person has 20% body fat and weighs 135 lbs., then 27 lbs. of this is fat. Everything else, which is sometimes referred to as the "lean mass" is 80% of their weight or 108 lbs. Of this lean mass, the component that can change the most is muscle tissue. Therefore, if a person monitors their change in percent body fat and weight they can also determine their change in muscle tissue. Muscle tissue can increase or decrease depending on a persons diet, activities, exercise and lifestyle.

Research has shown several interesting things about body composition and muscle tissue. Various studies have shown that the typical American loses muscle tissue and gains fat steadily beginning about age 20. The studies show that even people of standard weight, who maintain their same weight as they grow older, still gain fat and lose muscle tissue. A major study by Brozek and Keys of a large group of men showed the following changes in percent fat with age of people of standard weight. That is, people who maintained their correct weight per height-weight charts over time.

What this shows is that a person who weighs, for example, 160 lbs. at age 20 has 16 lbs. of fat (10.3%) and 144 lbs. of everything else (bones, muscle, organs, etc.). But at age 55, this same person who still weighs 160 lbs. has 40 lbs. of fat (25%) and 120 lbs. of everything else. Since muscle tissue is the component of "lean mass" that changes the most, this means that from age 20 to age 55, this person has lost 24 lbs. of muscle and replaced it with 24 lbs. of fat. Even though this person weighs the same at 55 as he did at age 20 his body has deteriorated substantially. The example given is for a man, but exactly the same thing happens to the typical American woman.

This deterioration did not have to happen to this person. It is due to the typical American lifestyle of too little exercise and too much fat in the diet. It has been proven that those who exercise regularly, along with a proper diet, do not lose muscle tissue or gain fat. In fact, even at age 50 and above it is possible to build muscle tissue back up and regain the correct balance between muscle, fat and weight. All that is necessary is the proper exercise and diet program.

It is important to note that this deterioration starts early. Even by the age of 25, the typical American has lost 3% of their body weight in muscle tissue and replaced it with fat. And this is just for those who maintain their correct weight. For those whose weight increases the situation is worse because almost all of the weight increase is fat. If a person monitors their percent body fat regularly, they can detect muscle loss early and take corrective action before serious changes take place.

Determine the Effectiveness of Exercise and Diet

Another very important use of percent body fat measurements is to monitor the effect of diet and/or exercise on muscle tissue and fat. For example, research has shown that when a person goes on a typical fad diet, with little exercise, they lose as much or more muscle tissue than fat. (Scales will not tell a person that this is happening, but measuring percent body fat regularly will.) Then, if this person goes off the diet and gains the weight back, they gain more fat back than they lost and less muscle tissue than they lost. The result is that they have more fat and less muscle than before the down-up cycle and are worse off than before the diet. Again, measuring percent body fat will show this whereas scales will not.

Of course, the way to reduce properly is through lots of exercise combined with a proper well-balanced diet. In this way it is possible for a person to actually gain muscle tissue while losing fat. Measuring percent body fat regularly will determine the effectiveness of the exercise-diet program being used.

Body Fat Versus Weight

There are many other things measuring percent body fat can show. For example, a person who is much too lean, particularly women, may not realize this and scales will not tell them. There are studies which indicate it is harmful for women to drop below 10 to 12% body fat. And, of course, we all know the problem of Anorexic girls and women who do not realize, or refused to believe, they are much too lean. Regular monitoring of percent body fat will show graphically and accurately that they are too lean and are also losing muscle and organ tissue with their inadequate nutrition intake. Positive proof of this through percent body fat measurements can help convince them that they need a better diet, higher in calories and nutrition.

Another use for percent body fat measurements concerns a much more common situation. This is the person who is the correct weight according to a height weight chart or even underweight according to these charts. They may also look reasonably fit when they look in a mirror and may think they are just fine. And yet, if they measure their percent body fat they may find they have too much fat. Their small, under-developed, probably little used muscles account for their light weight. Percent body fat measurements will show them they are overfat and under muscled and they will realize they need to go on an exercise program with correct food intake to replace fat with muscle.

And yet another possibility is a very strong, muscular, athletic person. They may have a weight considerably above what a height-weight chart would say they should have. If they believe the chart they may think they have too much fat and have to lose weight when, in fact, their extra weight is due to large muscles. This person might actually be very lean and if they were to go on a diet and lose weight almost all the loss would be muscle tissue. Measuring percent body fat would reveal this situation and show the person they were lean and that the extra weight was muscle and possibly even stronger bones which have a higher density. A scale cannot give this information. Only percent body fat measurements will show this.

A typical situation that exists when someone starts on a good exercise program combined with proper nutrition is that they find their weight is not changing even after several months. They may get discouraged and give it up, thinking their new regimen is not doing them any good. However, if they measured their percent body fat regularly they would find they were replacing fat with muscle and, in fact, benefiting themselves greatly. Thus, rather than becoming discouraged, they would be encouraged to continue.

Measuring Body Fat

Now that the importance of percent body fat measurements has been explained, we come to the question of how to measure it. There are several methods in use today, however, the most accurate are underwater weighing and Skinfold Caliper measurements. Underwater weighing tends to be more accurate than Skinfold Calipers for people above about 45% body fat. For people in the 15 to 45% range, Skinfold Calipers and underwater weighing are about equal in accuracy. For people less than 15% body fat, underwater weighing becomes progressively less accurate and can be seriously in error for very lean people. Skinfold Calipers are the most accurate method for people below 15% body fat. There are several other methods for measuring percent body fat such as circumference measurements, infrared, etc., but none are accurate and only provide an approximation.

Underwater weighing is impractical for most people and is generally only used in large facilities such as schools and hospitals. Skinfold Calipers are then the obvious answer for most applications. They are accurate and easy to use and can also be used in the home.

What is the Correct or Ideal Percent Body Fat?

What is the correct or ideal percent body fat? This is perhaps the most difficult question to answer. Not all people have the same ideal percent body fat. It varies with age and sex, and one person might be better at a higher or lower percent body fat than another person of the same age and sex. And the desirable body fat of athletes can vary depending on the sport. For example, swimmers seem to perform better at a higher percent body fat than runners.

Would you like to view a "Body Fat Rating Scale"?

But, some general guidelines and ranges can be given that are applicable to the vast majority. For men up to about age 30, 9 to 15 % is good. From age 30 to 50, 11 to 17% is a good range and from age 50 and up, 12 to 19%. A person should try to stay below the upper limits given and a person at the lower limit would be described as lean.

For women, the range up to age 30 is 14 to 21%, from 30 to 50 it is 15 to 23% and from 50 up it is 16 to 25%. Again, it is desirable to be below the upper limit, and a woman near the lower limit would be lean.

The percent body fat obtained by underwater weighing or skinfold calipers includes total body fat, not just that under the skin. In addition to the fat under the skin all people have internal fat, around organs, etc. A certain amount of fat is necessary for health and body functioning, sometimes referred to as essential fat. Many people, particularly women, try to get too lean. It is generally agreed that this is not healthy, and, in many cases can actually cause harm. Women should not try to get below the minimums given above.

It should be noted that the ranges given above are not the averages for the U.S. population, but are the desirable ranges. The actual averages for the population as a whole are much higher because of the large number of people with percent body fat well above the upper limit of the desirable ranges.

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