4.4: Assessing Body Composition

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Assessing Body Composition

As noted previously, BMI is the measurement used as a screening tool to quickly and inexpensively identify whether a person is at a healthy weight, underweight, overweight, or obese. BMI is not a measure of body composition, it will not tell you whether you are overfat, it will only tell you whether you are overweight. Understanding what the body is made up of (muscle, bone, water, and fat) is a better predictor of health, however, the tools used to measure body composition can be expensive, intrusive, not widely available, or difficult to standardize across observers or machines. 

When evaluating body composition, there are two general types of evaluations, body fat distribution and body fat percentage.

Body Fat Distribution

Fat can be stored as subcutaneous fat, fat stored just under the skin, or visceral fat, fat stored deeper in the body around the organs. High amounts of visceral fat lead to negative health implications including all-cause mortality^[5]. Thus carrying excess visceral fat around the abdomen places you at a higher risk of developing health issues.

Body fat distribution can be measured by calculating a person's waist circumference, waist-to-hip ratio, and waist-to-height ratio.

• Waist Circumference
  • Stand and place a tape measure around your middle, just above your hipbones. Measure your waist in inches just after you breathe out
    • Your waistline may be telling you that you have a higher risk of developing obesity-related conditions if you are
      • A man whose waist circumference is more than 40 inches
      • A non-pregnant woman whose waist circumference is more than 35 inches
• Waist-to-Hip Ratio
  • You can calculate your waist-to-hip ratio by taking your waist circumference and dividing it by your hip circumference. The World Health Organization categorizes high risk as a ratio above 0.85 for women and more than 0.9 for men.
• Waist-to-Height Ratio (WHtR)
  • You can calculate your waist-to-height ratio by dividing your waist circumference by your height. A waist-to-height ratio of more than 0.5 may put you at higher risk for heart disease and diabetes. The waist-to-height ratio is a good predictor of both BF% and Visceral Fat mass in men and women^[6].

Health Assessment: Body Composition

Understanding your body composition is an essential part of assessing overall health and wellness. This assessment will guide you through calculating three key measures: Body Mass Index (BMI), Waist-to-Hip Ratio, and estimated body fat percentage using the Navy Circumference Method.

Instructions

1. Calculate Your BMI

• Visit the BMI Calculator.

• Input your age, sex, height, and weight into the calculator.

• Record your BMI result and note which category it falls into (e.g., underweight, normal weight, overweight, or obese).

2. Determine Your Waist-to-Hip Ratio

• Measure your waist circumference at the narrowest point.

• Measure your hip circumference at the widest point.

• Calculate your waist-to-hip ratio using the formula:

  Waist-to-Hip Ratio = Waist Circumference ÷ Hip Circumference

3. Estimate Body Fat Percentage Using the Navy Circumference Method

• Visit the Body Fat Calculator.

• Input your sex, age, weight, height, and circumference measurements (neck, waist, and hips for women; neck and waist for men).

Reflection Questions

1. Analyze Your Results: Summarize the results from each of the three measures. How do they compare to the recommended ranges?

2. Reflect on Your Findings: How do you feel about these results? Were you surprised by any of them? Why or why not?

3. Set a SMART Goal for Body Composition: Create a Specific, Measurable, Achievable, Relevant, and Time-Bound goal to improve or maintain your body composition. For example: "Within 6 months, I will reduce my body fat percentage by 2%."

Additional Resources

• CDC BMI Information: Body Mass Index

• WHO Waist-to-Hip Ratio Info: Waist-to-Hip Ratio

• Exercise and Nutrition Tips: ChooseMyPlate.gov

This assessment will help you better understand your current health status and identify actionable steps for improvement.

Body Fat Percentage

Body fat percentage is a measure of the percentage of your body that is fat-free mass versus fat mass. There are several measurement tools to estimate body fat percentage, each has pros and cons mostly related to difficulty, cost, and availability.

• Bioelectrical Impedance Analysis (BIA)
  • Bioelectrical Impedance Analysis is likely the measuring method you are most familiar with. Have you ever used a scale that told you your body fat percentage? If so, you have used BIA. BIA devices emit a low-level electrical current through the body and measure the amount of resistance the current encounters. Based on the level of impedance, a pre-programmed equation is used to estimate body fat percentage. Fat tissue contains little water, making it a poor conductor of electricity; whereas, lean tissue contains mostly water and electrolytes, making it an excellent conductor. The most accurate BIA devices use electrodes on the feet and hands to administer the point-to-point electrical current. Because BIA devices primarily measure hydration, circumstances that may influence hydration status at the time of measurement must be taken into account. Recent exercise, bladder content, hydration habits, and meal timing can cause wide measurement variations and influence accuracy. However, this method is generally inexpensive, often portable, and requires limited training to use, making it a very practical option.
• Skinfold Calipers
  • Skinfold analysis is a widely used method of assessing body composition because of its simplicity, portability, and affordability. Some call the skinfold test the “pinch test” because the skin and underlying subcutaneous fat is pinched with calipers to measure the thickness. Skinfold measurement assumes that the amount of subcutaneous fat is proportionate to overall body fat. These numbers are plugged into an equation to generate an estimate of body fat percentage. The skinfold test is fairly accurate when administered properly.
• Hydrostatic Weighing (underwater weighing)
  • Hydrostatic weighing is difficult but has long been considered the “gold standard” for assessing body composition. A person is weighed when dry and then enters a water tank and is weighed while underwater. Since fat is less dense than muscle tissue, a person with more body fat will weigh less in the water than a similar person with more lean mass. Using the measurements, the density can be determined and converted into body fat percentage. With a small margin of error (around 1-2%) this method is very accurate. Unfortunately, the expense and practicality of building and maintaining a water tank limits access for most. This method is also challenging for people who are afraid of water, don’t feel comfortable in bathing suits, or are fearful of exhaling all air and sitting underwater without moving for a short time.
• Air Displacement Plethysmography
  • Air displacement plethysmography works similarly to hydrostatic weighing however it measures the displacement of air instead of water. The Bod Pod is the most commonly referenced machine. During the test, a person sits in a chamber that varies the air pressure allowing for body volume to be assessed. Air displacement provides a viable alternative for those with a fear of water. Like many other methods, the expense, availability, and training of personnel limits accessibility. Additionally, its accuracy is slightly less than underwater weighing.
• Dual X-ray Absorptiometry (DXA)
  • Replacing underwater weighing as the new “gold standard,” DXA provides a quick and pain-free method for measuring body fat by scanning the body. The patient lays down and is scanned by the DXA machine which takes about 6 minutes. Major disadvantages to this method are its high cost and the need for a trained professional to operate the equipment and analyze the results.

Special Highlight: Essential Fat and Women's Health

Essential fat refers to the minimum amount of fat necessary for the body to function properly. Women require a higher percentage of essential fat compared to men due to their unique physiological needs related to reproductive health. While men typically need about 3-5% essential fat, women require approximately 10-13%. This additional fat plays a critical role in hormone regulation, childbearing, and overall energy balance.

Key reasons for the difference:

• Reproductive Functions: Essential fat in women supports fertility by regulating hormones like estrogen and progesterone.
• Protection of Vital Organs: Adequate fat storage cushions organs and provides insulation for temperature regulation.
• Energy Reserves: Essential fat serves as a critical energy source during pregnancy and breastfeeding.

Maintaining adequate essential fat is crucial for health. Low energy balance—when energy intake does not meet energy expenditure—can have serious health implications, particularly for women. Signs of low energy balance include:

• Amenorrhea (Loss of Menstrual Periods): A key indicator of hormonal disruption due to insufficient fat and energy stores.
• Chronic Fatigue: Persistent tiredness and reduced endurance capacity.
• Weakened Immune Function: Increased susceptibility to illness.
• Decreased Bone Density: Higher risk of stress fractures and osteoporosis.

Striking the right balance between maintaining necessary essential fat and preventing excess storage is critical for overall health, hormonal stability, and physical performance.