Measures of Health: Both Fitness and a Healthy Weight Should be Goals

Reading the bathroom scale, especially after the holiday season, is often a traumatic event for many Americans. After their pulse returns to a normal rhythm, many people make the decision, once again, to lose weight. But is the number on the scale the only thing that matters? While losing excess weight is generally a healthful goal, fitness should be an important consideration as well, and using body weight alone to determine health can be misleading. When the accuracy of body mass index (BMI) for diagnosing obesity in the adult general population was tested using NHANES data, it showed more than half of the individuals with increased body fat percentage may be misclassified by calculations of BMI. Some individuals are heavier due to muscle mass, while others are thin, but have a high percent body fat. The number on the scale alone would not be able to provide this information. Therefore, considering other markers of fitness, such as body composition as measured by weight circumference, can lead to a more sustainable and healthier weight.

Defining a Healthy Weight

Defining what is a healthy weight has not been easy. Before 1980, doctors generally used weight-for-height tables – one for men and one for women – that included ranges of body weight for each inch of height. These tables were limited because they were based on weight alone, rather than body composition. Obesity was first defined by a group of international experts as weighing more than is appropriate for a given height, according to a widely accepted mathematical formula known as body mass index (BMI): kilograms/meters2. The International Obesity Task Force, commissioned in 1997 by the World Health Organization, defined obesity as a measurement of body mass index greater than 30kg/m2. This definition was based on positive associations between BMIs greater than 30 and risk factors for mortality and morbidity. The public learned about BMI in the late 1990s, when the government launched an initiative to encourage healthful eating and exercise, and it has been used (with some adjustments) ever since.

In 1998, the National Institutes of Health lowered the criteria for the “overweight” threshold for BMI from 27.8 to 25 to match international guidelines. The move added 30 million Americans who were previously in the "healthy weight" category to the "overweight" category. An adult who is considered "overweight" has a BMI somewhere between 25 and 29.9. However, if one calculates the BMI of many of today’s highest achieving athletes, a BMI of 30 or higher would mistakenly classify them as obese due to having a higher percent muscle mass. For example, a cohort study published in the journal Economics and Human Biology looked at the BMI of US baseball players over a 115-year period to examine trends in height, weight, and body mass from 1869 to 1983. They found that over that period, U.S. born Major League Baseball players have gained, on average, approximately 3 in. (7.6 cm) in height and 27.0 pounds (12.2 kg) in weight, which has contributed a 1.6-unit increase in the body mass index. Does this mean today’s baseball players are less fit than the Babe Ruths and Ty Cobbs of yesterday? Not so fast. What appears to be missing in the use of BMI to determine a healthy weight is a measurement of body fat.

Methods of Determining Body Fat

 

Methods to estimate body fat range from the less technical approaches, such as skinfold measurement and waist to hip ratio, to the more technological methods, including bioelectrical impedance, hydrostatic plethysmography and dual X-ray absorptiometry.

Normal Weight Obesity – Waist Circumference:

Recently, the concept of normal weight obesity (NWO) has begun to gain recognition. In 2006, De Lorenzo et al., described NWO as having a normal body weight and BMI <25 with an increased body fat percentage. Despite the fact that obesity by definition represents excess body fat, there does not seem to be agreement on a definition of obesity based on percent body fat or accepted cut-off values for individuals at higher risk, but there seems to be strong evidence that NWO is linked to metabolic dysfunction, often leading to metabolic syndrome and other risk factors. A study that looked at the mortality risk of patients with coronary artery disease (CAD), comparing body mass index (BMI) with measures of central obesity, found normal weight with central obesity is associated with the highest risk of mortality.

Additionally, according to the National Institutes of Health, a high Waist Circumference (WC) is associated with an increased risk for type 2 diabetes, dyslipidemia, hypertension, and cardiovascular disease when BMI is between 25 and 34.9. Changes in waist circumference over time can indicate an increase or decrease in abdominal fat, and increased abdominal fat is associated with an increased risk of heart disease.

 

To determine waist circumference, locate the upper hip bone and place a measuring tape around the abdomen (ensuring that the tape measure is horizontal. The tape measure should be snug but should not cause compressions on the skin. Then take a look at the overall health risk and obesity class table below.

 

Finding the Right Balance

A recent publication in Nutrition Today suggests that “while consumers agree that both diet and physical activity are important, many do not connect balancing calories from food and beverages with calories expended through physical activity as an essential behavior to achieve and maintain a healthy weight.” The authors go on to recommend that “nutrition, fitness, and health professionals must develop strategies that inspire individuals to take action toward balancing calories consumed with expenditure.” Evidence points to the need to achieve fitness that results in a reduced percent body fat, rather than relying solely on weight for height. Encouraging routine physical activity to build muscle and meeting nutritional needs by eating smarter, are winning approaches to sustainable and rewarding health.

So, the next time the bathroom scale displays a displeasing number, remember that it is just one number, and that other numbers such as Waist Circumference help to paint a more complete picture of overall health. Focus on fitness in the New Year and give the bathroom scale a rest!

 

For science-based guidance for improving health through physical activity, see the Department of Health & Human Services’ Physical Activity Guidelines for Americans.

 

References:

Coutinho T. et. al. Combining body mass index with measures of central obesity in the assessment of mortality in subjects with coronary disease: role of "normal weight central obesity, J Am Coll Cardiol. 2013 Jul 16;62(3):261.

Lavie C.J. et. al. Exercise is Medicine-The Importance of Physical Activity, Exercise Training, Cardiorespiratory Fitness and Obesity in the Prevention and Treatment of Type 2 Diabetes, US Endocrinology, vol. 9, (2) 2013.

Oliveros E. et. al. The Concept of Normal Weight Obesity, Progress in Cardiovascular Disease, doi: 10.1016/j.pcad.2013.10.003.

Morris RD and Rimm AA, Association of waist to hip ratio and family history with the prevalence of NIDDM among 25,272 adult, white females, Am J Public Health, 1991 April; 81(4): 507–509.

Reinhardt Kapsak W et al. Confusion on All Sides of the Calorie Equation, Nutrition Today, vol. 48 (5), Sept. 2013.