Chapter 6: What is a Healthy Body Weight?

Learning Objectives

By the end of this chapter, you will be able to:

• Describe the body’s use, storage, and balance of energy.
• Describe the process of calculating body mass index (BMI).
• Describe factors that contribute to weight management.
• Identify evidence-based nutritional recommendations.

In this section, we look at the complex factors that interact to affect body weight, ways to assess body weight, and recommendations for maintaining a healthy weight. Society and Environment contribute to body weight, as do individual physiology, genetics, and behavior. We will also discuss the health risks of being underweight and overweight, learn evidence-based solutions to maintain body weight at the individual level, and assess the current state of combating the obesity epidemic in the United States.

Obesity and Society

The number of people who struggle with overweight and obesity is rising rapidly in the US and around the world. A new term to describe factors that increase obesity is “obesogenic.” An obesogenic environment is defined as “an environment that promotes increased food intake of non-healthful foods, and physical inactivity.” The CDC reports that in the United States, 41.9% of adults were obese during the years 2017-2020^[1]. Obesity rates are highest among those in lower income and educational levels. Risk of obesity varies with race/ethnic factors as well. In Washington, American Indian/Alaska Native and Native Hawaiian/Pacific Islander populations had the highest age adjusted rates of obesity, with non-Hispanic whites and Asians having the lowest.

The health consequences of excess body fat include increased risk of cardiovascular disease, Type 2 diabetes, and some cancers. There are financial costs of obesity as well; a 2010 study found that being obese costs a woman $4,879 and costs a man $2,646 per year, mostly in health care costs and lost wages. In the United States, obesity-related illness costs around $173 billion each year^{[2, 3]}. No one WANTS to become obese, so what are the factors causing rates of obesity to rise so rapidly? What can we do about these factors?

Many factors contribute to high obesity rates. The fast-food industry grows even when the economy struggles. Portion sizes are growing, as seen by the popularity of the “super-size” marketing boom. Another factor is the increase in inactivity in the US. Between 1960 and 2000, more than 123 million vehicles were added to American roads. Escalators, elevators, and horizontal walkways now dominate shopping malls and office buildings, factory work has become increasingly mechanized and automated, the typical American watches than four hours of television daily. In many workplaces, the only tools required are a chair and a computer. Many obesogenic factors come from modernization, industrialization, and urbanization.

With obesity at epidemic proportions in America it is paramount that policies be implemented or reinforced at all levels of society, and include education, agriculture, industry, urban planning, healthcare, and government. Reversing and stopping obesity are two different things. The former will require much more societal and individual change than the latter. The following are some ideas for constructing an environment in America that promotes health and confronts the obesity epidemic:

• Individual Level Actions
  • Purchase less prepared foods and eat more whole foods.
  • Decrease portion sizes when eating or serving food.
  • Eat out less, and when you do eat out choose low-calorie options.
  • Walk or bike to work. If this is not feasible, walk while you are at work.
  • Take the stairs when you come upon them or better yet, seek them out.
  • Walk your neighborhood and know your surroundings. This benefits both health and safety.
  • Watch less television.
• Community Level
  • Request that your college/workplace provides more access to healthy low-cost foods.
  • Support changes in school lunch programs—this is happening now but needs vocal parents to continue!
  • Participate in cleaning up local green spaces and then enjoy them during your leisure time, get outside!
  • Patronize local farms and fruit-and-vegetable stands.
  • Talk to your grocer and ask for better whole-food choices and seafood at a decent price.
  • Ask your favorite restaurant to serve more nutritious food and to accurately display calories of menu items.
• National Level
  • Support policies that increase the walk-ability of cities.
  • Support funding for national programs that fight obesity, such as those through the USDA, NIH, and CDC.
  • Support policies that support local farmers and the increased access and affordability of healthy food.

Indicators of Health: Body Mass Index, Body Composition, and Fat Distribution

Although the terms “overweight” and “obese” are often used interchangeably and considered as gradations of the same thing, they can denote different things. Body weight is the sum of lean body weight (including bone, muscle, and organs), water weight, and weight from body fat. “Overweight” refers to having more weight than is typical for a particular height. “Obese” generally refers to having excess body fat. Because weight is the sum of numerous components, additional information is useful in determining if a person is overweight or obese.

The “ideal” healthy body weight for a particular person is dependent on many things, such as frame size, sex (hormone profile), muscle mass, bone density, age, and height. The perception of the “ideal” body weight is also dependent on cultural factors such as depictions of beauty in advertising and other media.

The Body Mass Index (BMI)

A simple tool for evaluating weight and health risk is the body mass index (BMI). BMI uses height and weight for a quick, inexpensive estimate of health risks related to body size. BMI is used to indicate whether an individual may be underweight (with a BMI less than 18.5), overweight (with a BMI over 25), or obese (with a BMI over 30). The BMI is defined as the body mass divided by the square of the body height; it is universally expressed in units of kg/m², calculated using mass in kilograms and height in meters.

The categories currently defined by the BMI are given in Table 6.1. There is discussion about where the lines between categories should be, and they have even changed over the years. In 1998, the CDC lowered the maximum “normal” or “healthy” BMI value from 26 to 25, leading comedians to joke that they had been healthy when they went to bed and overweight when they woke up. Some tables of BMI values include a category of “Extremely obese” at > 40.

Table 6.1 Categories of body mass index.

Category	BMI
Underweight	< 18.5
Normal weight	18.5 – 24.9
Overweight	25 – 29.9
Obese	> 30.0

The National Heart, Lung, and Blood Institute and the CDC have automatic BMI calculators on their websites:

• Calculate Your BMI | NHLBI, NIH
• Adult BMI Calculator | BMI | CDC

Figure 6.2 shows that either low or high BMI increases the mortality risk, which is the chance of dying from any cause. The J-shaped curve of mortality risk is the lowest between 18 and 25, but the risk increases gradually. Like a teacher assigning a letter grade, the decision of exactly where to draw the lines for underweight, normal weight, overweight and obese are somewhat arbitrary.

Limitations of the BMI

It is simple to calculate BMI, and so it is widely used. However, BMI does not consider body composition or fat distribution, both of which are important additional predictors of disease risk. For example, because muscle is denser than fat, muscular individuals may calculate a higher BMI than a couch potato of the same weight. Elite athletes may have BMI values above 25, indicating overweight, when they have low body fat and are not at the risks of others in the “overweight” category. Other groups for whom BMI calculations might be misleading include children, pregnant women, and the elderly, who may have experienced bone and muscle density losses.

According to the CDC, “For most people, BMI is a good indicator of whether they have too much or too little body fat. However, BMI is not a direct measure of body fat. BMI cannot distinguish fat mass from lean body mass (muscle and bone). BMI also cannot indicate where fat is located in the body. BMI is moderately to strongly associated with other measures that do capture the amount, type, and distribution of fat. A health care provider can help evaluate a person’s health risks related to their BMI and body fat.”^[4]

Measuring Body Fat Content

Water, organs, bone, fat, and muscle make up a person’s weight. Having excess fat mass may be indicative of disease risk, but fat mass varies with sex, age, and physical activity level. Females have more fat mass, which is needed for reproduction and, in part, is a consequence of different levels of hormones. The optimal fat content of a female is between 20 and 30 % of her total weight and for a male is between 12 and 20 %. Fat mass can be measured in a variety of ways.

• Underwater weighing requires a specialized chamber of water large enough for a person to be submerged. The subject is weighed outside the chamber and then weighed again while immersed in water after blowing air out of the lungs. Muscle, bone, and organs are denser than water and will sink, while fat is less dense and will cause a person to float. Measuring and comparing a person’s weights in and out of water allows a calculation of body fat percentage.
• Skin-fold measurement. One of the simplest and lowest-cost methods involves measuring the thickness of the fat layer under the skin at various parts of the body. As measured by a set of calipers, the thickness of the skin pinched on various parts of the body (arm, back, hip) is compared to sex-based charts to estimate body fat percentage. A drawback is that a small deviation in the body site tested can make a big difference in the results, so training and consistency of the technician performing the test is important.
• Bioelectric Impedance Analysis (BIA) is based on the speed with which electricity passes through the body. Because fat and lean tissue have different electrical conductivity, the rate at which a small amount of electricity passes through the body can be used to estimate body composition. BIA devices are available for home use, commonly marketed as body composition scales.
• Dual-energy x-ray absorptiometry was originally designed to measure bone density, but this technique can also determine body fat content. Sophisticated medical equipment measures the absorption of two low-dose x-ray beams as they pass through the body. Using mathematical formulas, body fat percentage and distribution can be determined.

Measuring Fat Distribution

Total body-fat mass is one predictor of health; another is how the fat is distributed in the body. You may have heard that fat on the hips is less risky to health than fat in the belly—this is true. Fat deposits differ physiologically based on their location in the body. Fat in the abdominal cavity is called visceral fat and it is a better predictor of disease risk than total fat mass. Visceral fat releases hormones and inflammatory factors that contribute to disease risk. The only tool required for measuring visceral fat is a measuring tape; measure the waist circumference just above the navel. Men with a waist circumference greater than 40 inches and women with a waist circumference greater than 35 inches are predicted to face greater health risks.

The waist-to-hip ratio is often considered a better measurement than waist circumference alone in predicting disease risk. To calculate your waist-to-hip ratio, use a measuring tape to measure your waist circumference and your hip circumference at its widest part. Divide the waist circumference by the hip circumference to arrive at the waist-to-hip ratio. Observational studies have demonstrated that people with “apple-shaped” bodies (more weight around the waist) have greater risks for chronic disease than those with “pear-shaped” bodies (more weight around the hips). A study published in the November 2005 issue of Lancet with more than twenty-seven thousand participants from fifty-two countries concluded that the waist-to-hip ratio is highly correlated with heart attack risk worldwide and is a better predictor of heart attacks than BMI^[5]. Abdominal obesity is defined by the World Health Organization (WHO) as having a waist-to-hip ratio above 0.90 for males and above 0.85 for females. A 2020 meta-analysis of 40 studies supports the connection between abdominal obesity and health risks, with a higher predictive value for heart disease than BMI^[6].

Metabolic Syndrome

Metabolic syndrome is the name of a group of risk factors that collectively raise the risk of heart disease, type II diabetes, and stroke. Metabolic syndrome is diagnosed when any three of the following five conditions are present:

• Abdominal obesity
• Elevated plasma triglycerides
• Low HDL ‘good’ cholesterol
• High blood pressure
• High fasting blood glucose

Metabolic syndrome increases the risk of:

• Coronary heart disease
• Heart attack
• Stroke
• Type II diabetes

Ways to prevent metabolic syndrome:

• Diet rich in wholes grains, vegetables, and lean proteins while being low in saturated and trans fats, added sugar, sodium and processed foods.
• At least 150 min per week of moderate intensity exercise.
• Weight loss due to balance of healthy eating and moderate exercise.

For more information: Metabolic Syndrome | American Heart Association

References

1. Centers for Disease Control and Prevention. “Adult Obesity Facts.” https://www.cdc.gov/obesity/adult-obesity-facts/ Updated May 14, 2024. Accessed March 2, 2026.
2. Dor, A., C. Ferguson, C. Langwith and E. Tan. A Heavy Burden: The Individual Costs of Being Overweight and Obese in the United States. George Washington University School of Public Health and Health Services. 2010. https://hsrc.himmelfarb.gwu.edu/cgi/viewcontent.cgi?article=1211&context=sphhs_policy_facpubs Accessed Jan. 31, 2021.
3. U.S. Department of Health and Human Services. “About Obesity.” https://www.cdc.gov/obesity/php/about/index.html Updated January 23, 2024. Accessed August 27, 2024.
4. Centers for Disease Control and Prevention. “BMI Frequently Asked Questions.” https://www.cdc.gov/bmi/faq/index.html. Updated June 28, 2024. Accessed August 27, 2024.
5. Yusuf, S. et al. “Obesity and the Risk of Myocardial Infarction in 27,000 Participants from 52 Countries: A Case-Control Study.” Lancet 366, no. 9497 (2005): 1640–9. http://www.ncbi.nlm.nih.gov/pubmed/16271645
6. Darbandi M, Pasdar Y, Moradi S, Mohamed HJJ, Hamzeh B, Salimi Y. Discriminatory Capacity of Anthropometric Indices for Cardiovascular Disease in Adults: A Systematic Review and Meta-Analysis. Prev Chronic Dis 2020;17:200112.

Attributions

Adapted by Pattie S. Green, Ph.D., and Jonathan E. Pottle, Ph.D., Tacoma Community College from An Introduction to Nutrition (Zimmerman), which is licensed under CC BY-NC-SA 3.0. Specifically, the following parts were adapted here:

• 11.1: Prelude to Energy Balance and Body Weight
• 11.2: Indicators of Health- Body Mass Index, Body Composition, and Fat Distribution