The Basics of Body Composition

Body composition is the ratio of fat mass to fat-free mass (ACSM, 2013). Body composition is often expressed as the percentage of total body fat one has, while the remainder is everything else (bone, muscle tissue, organs, teeth, connective tissue, body water etc.) (Kenny et al., 2015). It is important to note that while the term “fat” often comes with a negative connotation, body fat is incredibly important. While excess body fat comes with an increased risk for various chronic illnesses (more on this in the section titled Body Fat), body fat is necessary for various functions (ACSM, 2013). The risk of low body fat and high body fat will be discussed in more detail below.

Body weight

According to the National Center for Biotechnology Information (n.d), body weight can be defined as “The mass or quantity of heaviness of an individual. It is expressed by units of pounds or kilograms.” The term overweight is defined by Fahey et al. (2020) as “total body weight above the recommended weight for good health as determined by large-scale population surveys.” Body weight norms, or the range of healthy body weights, are typically based on height. It is not uncommon for individuals to be concerned about their weight. The problem with focusing too much on weight is that weight alone doesn’t tell us anything about what our body composition is. Excess weight due to excess fat tissue is very different from excess body weight due to muscle mass. The former has the potential to increase one’s risk of certain chronic diseases, while the latter is often a result of skeletal muscle training.

Body fat

Adipose tissue, often called body fat, is the body tissue where we store fat (Fahey et al., 2020). As mentioned above, body fat is typically expressed as a percentage (Kenny et al., 2015). This is a percentage of the whole body. So if someone’s body fat percentage is 25%, that means 25% of their body is fat tissue, and 75% is made up of everything else. Body fat is necessary for bodily function. It is needed for various organs and systems in our body to function properly. For example, our nervous system needs fat tissue, as well as our brain, heart, lungs, and mammary glands. Body fat is needed for the protection of body organs, thermoregulation, and energy storage (Fahey et al., 2020)and is a component of our cell membranes. Essential fat, or the bare minimum fat our body needs to function, is 3-5% in males and 8-12% in females. This percentage is higher in females due to fat deposits necessary for reproduction, including the uterus and breasts (Fahey et al., 2020). Ideal body fat, separated by sex and age as defined by (Gallagher et al., 2000) in the American Journal of Clinical Nutrition, is as follows:

Females

Age 20-39: 21-33%

Age 40-59: 23-34%

Age 60-79: 24-35%

Males

Age 20-39: 8-19%

Age 40-59: 11-21%

Age 60-79: 13-24%

If you are below these ranges, you would fall into the category of underfat, and above these ranges as the overfat and obese categories. According to ACSM (2013), too much body fat is associated with chronic diseases, including hypertension (high blood pressure), metabolic syndrome, dyslipidemia (unbalanced lipids/ cholesterol), type 2 diabetes, cardiovascular disease, and events including stroke and heart attack. Being underweight increases various risks including, but not limited to, the risk of stunted growth, respiratory infection and other infections in children, osteoporosis and bone fractures, cardiovascular disease, hormonal imbalance leading to fertility issues in both males and females, ovulation dysfunction, and amenorrhea in females, depression, and finally, evidence exists that individuals who are underweight may have an increased risk of premature death when compared to individuals of a healthy weight (Roh al., 2014; Park et al., 2023; Park et al., 2017; Jung et al., 2017; Park et al., 2023; WHO, 2024; Dobner & Kaser, 2017; Lim & Park, 2016).

Overweight vs Obese

According to Fahey et al. (2020), overweight is a bodyweight that falls above the recommended range that is based on one’s height. As mentioned, weight (typically measured in lb or kg) in itself does not give us information about body composition. Excess weight due to excess fat tissue is very different from excess body weight due to muscle mass. The former can lead to disease, while the latter is often a result of muscular training. It is especially important for athletes to pay less attention to overall body weight or body size, and it can be reasonable for them to give more attention to body composition (Kenny et al., 2015). Two individuals of the same sex, age, weight, and height can have very different body composition. With that said, spending too much time focusing or concerning yourself with body composition can be unhealthy as well. Too much attention and concern may lead people down various negative pathways that could include overtraining, disordered eating, and relative energy deficiency in sport.

Various definitions of obesity exist. Obesity can be viewed as “a more serious degree of overweight that carries multiple major health risks” (Fahey et al., 2020). The concern with this definition, and similar ones, is that it does not address body fat but rather just overall weight. As mentioned above, weight in itself (without distinguishing if it is excess fat weight) is not the problem. Any potential negative consequences of excess body weight come when the weight is caused by fat.

An arguably better definition is “ a complex disease involving having too much body fat.” (Mayo Clinic Staff, n.d.). The latter definition addresses the disease concern, which is excess adipose tissue. Moving forward in this text, we will assume overweight relates to someone outside the “ideal” weight range based on their height, and obesity is an excess of adipose (fat) tissue.

BMI

Body Mass Index (or BMI) is a tool used to compare weight to height (ACSM 2013). The formula to determine BMI is weight in Kg (to go from lb to kg, divide by 2.2) divided by height in meters squared (1 inch is 2.54 cm and 1 cm is .01 meters).

BMI = Weight (in kg) / Height² (in meters)

According to the ACSM (2013), health problems related to obesity increase after a BMI of 25 kg.m. A BMI of 25 begins the overweight category, and a BMI of 30 or above suggests one is obese. It is once again important to note that BMI does not address body composition, and thus two individuals with the same BMI could have very different body compositions. BMI is a noninvasive tool that is often used, but it is important to note its limitations, which are more pronounced in individuals who are athletic and have a higher-than-normal muscle mass.

BMI (Kg. Mm²)

Underweight: <18.5

Normal: 18.5-24.9

Overweight: 25.0-29.9

Obesity: >30.0

Adapted from Executive Summary of the Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, (1998).

Waist Circumference

Hopefully, at this point, it is clear that body fat percentage yields information about a person’s general fitness, while body weight in itself gives us very little insight. Where body fat is stored is important to address. Visceral fat is fat that is located around organs, while subcutaneous fat is fat that is located under the skin (Fahey et al., 2020). More visceral fat distribution is linked to a greater risk of metabolic syndrome in comparison to subcutaneous fat. Additionally, excess body fat that is primarily around the torso/ trunk region is more detrimental to overall health than fat that is distributed in the hip and thigh region of the body (ACSM, 2013). Excess fat tissue in the abdominal region is termed android obesity, while excess fat tissue in the hips and thighs is termed gynoid obesity. Having android obesity puts someone at higher risk of developing the chronic illnesses associated with obesity (hypertension, metabolic syndrome, dyslipidemia, type 2 diabetes, and cardiovascular disease) than those with gynoid obesity.

Because of this, waist circumference measurements can be another tool to assess disease risk related to excess adipose tissue. Waist circumference measurements can be taken with a cloth tape. According to the ACSM (2013), waist measurements should be taken directly above the iliac crest. Measurements should be taken without compressing the skin. Ideally, two measurements should be taken, and provided there is not more than a 5mm difference between the two measurements, the average of the two should be used. According to the Center for Disease Control and Prevention (n.d.), a circumference greater than 40 inches in males and 35 inches in females increases one’s risk of obesity-related illnesses.

More information on BMI and waist circumference can be found on the CDC BMI Website.

Assessing Body Fat

Different methods exist to measure body fat. Below, these methods will be briefly summarized.

Each method of measuring body fat has different benefits. Some measurements are more precise but others are more convenient. Ways to assess body composition include Densitometry, Duel- energy X-ray absorptiometry, skinfold fat thickness measurements, and bioelectrical impedance procedures (Kenny et al., 2015). Densitometry is measuring an individual’s body density, and then using that to determine body composition. In order to do this body volume and body mass is needed. Body volume can be measured via hydrostatic weighing (or underwater weighing) which assess water displacement, and body mass is simply body weight. Air plethysmography is another way to measure body volume, in this case air displacement is used instead of water displacement. Duel- energy X-ray absorptiometry (DEXA) uses a Dexa machine to measure bone density as well as overall body composition. Densitometry and Duel- energy X-ray absorptiometry are both highly accurate ways to assess body composition. With that being said, they require more equipment than other methods. Skinfold fat thickness assessments use skinfold calipers to measure the thickness of skinfold fat. This equipment needed for this is far less expensive, but training is necessary in order to perform the assessment accurately. Finally a bioelectrical impedance uses a current to measure the electrical conductance through the body (Kenny et al., 2015). Water is a conductor, and the majority of body water is stored in our fat free mass, so fat free mass increases the speed of conduction, and fat mass slows it. This method requires very little training, and is relatively inexpensive compared to other methods. bioelectrical impedances can be simple hand held devices, and now can even be found in some bathroom scales.

Acknowledging The Obesity Epidemic

The term “obesity” is certainly something you have heard about prior to reading this chapter. It is well known the US has a high prevalence of obesity. In 2022, the Center for Disease Control and Prevention (n.d.), reported that every state and territory in the US had a greater than 20% adult obesity prevalence, with 19 states having a prevalence between 35% and 40%, and 3 states with a prevalence over 40%. More specifics about states, and other variables, including education level breakdowns as well as differences across race and ethnicity, can be found at the CDC website linked below. It is important to note that BMI is the tool used to categorize individuals as obese (BMI > 30.0 Kg. m-2). While it is well known that BMI is not the best measure of obesity, it is beneficial when we are looking at data for a large group, and the results are more accurate with non-athletic individuals (as athletic individuals tend to have a greater percentage of muscle mass in comparison to non-athletes). So while BMI is not the greatest measure, it is still very clear that obesity as well as the chronic illnesses associated with it (that were discussed above) are major health concerns. It is also important to note that while obesity is a problem in the United States, it is also a problem that is not restricted to the US or even to more industrialized countries. According to the World Health Organization (n.d.), it is estimated that 115 million individuals in developing countries are also dealing with health issues directly related to obesity.

Resources related to the obesity epidemic:

CDC Adult Obesity Prevalence Maps

World Health Organization (WHO) on Controlling the global obesity epidemic

Acknowledging Weight and Body Fat As Just One Component of Health

While the obesity epidemic is not a problem that should be ignored, it is also important to acknowledge that being overly concerned about body weight or body fatness to the point that it is all-consuming is not healthy either. Body composition is one indicator of disease risk, and we must also consider physical activity, nutrition, and other areas of fitness as well as mental health. It is important to note that there is not one ideal body weight, shape, or size. As mentioned previously, too much attention and concern may lead people down various negative pathways that could include overtraining, disordered eating, and RES-S (relative energy deficiency in sport).

Using the resources provided, spend some time defining, and familiarizing yourself with the terms overtraining, disordered eating, and RED- S.

Relative Energy Deficiency in Sport (REDs)

What Is Disordered Eating?

Overtraining: What It Is, Symptoms, and Recovery

Practical Applications/Laboratory Activities

Different labs activities can be conducted for body composition. Some options include calculating BMI, measuring waist circumference, or using BIA to determine estimated body composition. With that said the author strongly believes if doing a body composition activity will have a negative effect on an individual (mentally, emotionally, or behaviorally) then the assessment should not be completed.

Optional Activities:

1) BMI Calculation and Classification:

 BMI = Weight (in kg) / Height² (in meters)

BMI (Kg. Mm²)

 Underweight: <18.5

Normal: 18.5-24.9

Overweight: 25.0-29.9

Obesity: >30.0

Adapted from Executive Summary of the Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, (1998).

2) Waist Circumference Measurement and Classification:

Equipment: Cloth tape

Take measurements:

• 1) Measurements should be taken directly above the iliac crest.
• 2) Measurements should be taken without compressing the skin.
• 3) Take two measurements.
• 4) Average the results of the two measurements (as long as there is not more than a 5mm difference between the two measurements).
• 5) Use the chart below to determine waist circumference health risk

Note: Because of physiological differences across the sexes, the category standards are broken down by sex. Please see “Sex and Gender In This Text” at the beginning of this text for more clarification.

 Waist Circumference Risk Criteria for Adult Females

Very Low Risk	Low Risk	High Risk	Very High Risk
<70cm (<28.5in)	70-89 cm (28.5-35.0in)	90-110 cm (35.5-43.0in)	>110cm (>43.5)

Adapted from Bray (2004)

Waist Circumference Risk Criteria for Adult Males

Very Low Risk	Low Risk	High Risk	Very High Risk
<80cm (<31.5in)	80-99 cm (31.5-35.0in)	100-120 cm (39.5-47.0in)	>120cm (>47.0)

Adapted from Bray (2004)

3) If you have access to a BIA (bioelectrical Impedance), follow the specific instructions that are provided with the instrument. Once you have results, then you can compare them with the “ideal body fat range” (see above: Body fat) or those below from the American Council on Exercise (ACE).

Note: Because of physiological differences across the sexes, the category standards are broken down by sex. Please see “Sex and Gender In This Text” at the beginning of this text for more clarification.

Body Fat % for Adult Females

Essential Fat	Athletic	Fitness	Acceptable	Obese
10-13%	14-20%	21-24%	25-31%	>32%

Adapted from ACE (acefitness.org)

Body Fat % for Adult Males

Essential Fat	Athletic	Fitness	Acceptable	Obese
2-5%	6-13%	14-17%	18-24%	>25%

Adapted from ACE (acefitness.org)

NOTE: No less than 10-13% body fat in females and 3% in males is recommended (The Cooper Institute, 2009)

Chapter Overview

In this chapter, you learned about body composition. Body composition is the ratio of fat mass to fat-free mass (ACSM, 2013). Typically, when we are assessing body composition, we look to measure body fat, which is then expressed as a percent of the overall body that is made up of adipose (fat) tissue. The difference between looking at body composition or body fat percentage vs. body weight was discussed in detail. According to the National Center for Biotechnology Information (n.d), body weight can be defined as “The mass or quantity of heaviness of an individual.” It is expressed by units of pounds or kilograms and thus does not take composition into account.

Overweight and obese have become commonly used terms and talked about conditions that affect many individuals not only in the US but worldwide. It is important to understand that someone who is overweight has a body weight that is above the recommended range for the individual’s height Fahey et al. (2020), while “obesity is a complex disease involving having too much body fat.” (Mayo Clinic Staff n.d.). The associated health concern is linked less to weight and more to an excess in body fat. It is also important to note that while too much body fat is unhealthy and increases one’s risk of many chronic illnesses, being underfat is also extremely unhealthy. Additionally, it is also important to mention that too much focus on weight and appearance can lead to some negative outcomes as well.

Body Mass Index is a widely used tool to indicate when an individual is underweight, a normal weight, overweight, or obese, but certainly has limitations. Body Mass Index (or BMI) does not assess body composition and only compares weight to height (ACSM 2013). It is going to be less reliable as a tool for individuals with higher muscle mass. Looking at waist circumference can be helpful to determine if someone stores a high amount of fat in the torso/ trunk region (android obesity) as storing adipose tissue in this region is associated with more disease risk (ACSM, 2013). Many methods to assess body fatness exist.

Each method of measuring body fat has different benefits. Some measurements are more precise, but others are more convenient. Ways to assess body composition include Densitometry, dual-energy X-ray absorptiometry, skinfold fat thickness measurements, and bioelectrical impedance procedures (Kenny et al. 2015).

Obesity is a problem in the US, as well as in other developed and developing countries ( World Health Organization, n.d.),. While the obesity epidemic is not a problem that should be ignored, it is also important to acknowledge that being overly concerned about body weight or body fatness to the point that it is all-consuming is not healthy either. Body composition is only one indicator of disease risk.

Key Terms/Phrases

• body composition
• body weight
• overweight
• adipose tissue
• body fat percentage
• obese
• under fat
• body mass index