What Is the Goal of Obesity Screening?
Like any disease, obesity is associated with a variety of health consequences ranging from risk for other diseases (like diabetes and high blood pressure) to decreased quality of life. In severe cases, obesity can also shorten your life span. For this reason, it is important to identify who does and who does not have obesity as well as to find out who might be at risk to develop obesity.
By identifying those at risk, we can take steps to prevent further weight gain and prevent obesity. And, if we catch obesity early, we can intervene before it becomes severe. Without screening, many individuals won’t know whether their weight poses a risk to their health.
We can even screen children for obesity risk. It has long been observed that 40% of overweight children continue to be heavy during adolescence, and 75% to 80% of adolescents with obesity will remain obese as adults.
What Makes a Good Screening Test?
Body Mass Index
The most common tool used to screen for obesity is called the body mass index (BMI). However, many now agree that it is not the best tool. BMI is a good screening tool because it is free, easy to reproduce, and without risk.
The history of the BMI is quite interesting. It was invented in 1832 by Adolphe Quetelet, a Belgian mathematician and astronomer. He observed that, other than shortly after birth and during puberty, “weight increases as the square of the height.” The term, “body mass index,” was coined by Ancel Keys in 1972 (https://en.wikipedia.org/wiki/Body_mass_index).
BMI is calculated by taking your weight in kilograms and dividing it by your height squared. Or, if you prefer Imperial units, take your weight in pounds, and divide it by your height squared, and then multiply by 703, like this:
For example, if you are 200 pounds and 5 feet 10 inches tall (70 inches), your BMI would be:
According to the World Health Organization (WHO), a BMI that is too low can indicate malnutrition, an eating disorder, or another health problem, whereas a BMI that is too high can indicate obesity. These ranges of BMI are valid only as statistical categories (see Table 5-1).
Although the ranges listed in Table 5-1 are observed for classification purposes in the United States, other countries use different definitions. Some ethnicities have a high health risk even at BMI measurements considered “normal” in America. For example, practitioners in both Hong Kong and Japan consider a BMI greater than or equal to 25 to be obese.
Also keep in mind that these are adult ranges—for children aged 2 to 20 years, you can still calculate a BMI; however, instead of using fixed cut-offs like those in Table 5-1, it is better to plot them on a BMI-for-age graph and to calculate their BMI percentile, like we monitor childrens’ height and weight. Children with a BMI between the 85th and 95th percentile are overweight, and above the 95th percentile (meaning that they are heavier than 95% of all children) have obesity.
Although BMI is useful for estimating health risk, another way to think about your weight is body composition; that is, “How much of your body is fat weight versus lean weight?” Body composition is not typically used as a screening tool because there are lots of ways to measure it and the results achieved by the different techniques are not always the same. It requires specialized equipment, so it is more difficult to obtain than is BMI. Moreover, some of the technologies available might not be suitable for all people (for example, body-fat scales use an electrical current and are not considered safe for people who are pregnant or who have a pacemaker).
Nevertheless, body composition is useful to estimate your level of fitness. Your body is made up of fat, bone, water, and muscle. Body composition measurements can provide you with an estimate of the amount of your body that is fat. Two people at the same BMI can have a very different body compositions —for example, one might have a sedentary life style and have low muscle weight and high fat weight—and therefore have a high health risk, whereas another might be very active and physically fit, having a high muscle weight and low fat weight—and therefore have a low health risk.
Many techniques are used to measure body composition. The most common is called bioelectrical impedance analysis (BIA). BIA is used on the different body composition devices incorporated into scales and/or hand-held units. BIA uses the resistance of electrical flow through the body to estimate body fat. It can be affected by hydration status, although some scales are more resistant to this effect than are others. BIA devices range from inexpensive household scales to very expensive medical-grade scales.
The most accurate and increasingly available technology is dual energy X-ray absorptiometry (DEXA or DXA) scanning. Many people are familiar with this technology because it is used for osteoporosis screening. The measurements are highly reproducible making them excellent for research purposes.
For decades, the “gold standard” way to measure body composition was underwater weighing. The individual is placed in a pool of water and fully submersed. By doing this, we can measure the person’s volume, and then calculate their body composition. When done properly, underwater weighing is very accurate.
Like underwater weighing, air displacement plethysmography measures air displacement instead of water displacement. This way you don’t need to get wet! For this test, you sit in an instrument that looks like a large egg and the machine determines how much air you displace.
Another tool calculates skin-fold measurements, using calipers. Many different areas can be measured, and there are formulas to convert skin-fold thicknesses to body fat percentages. However, there can be a lot of variability from person to person, and it requires special training for the individual to be able to calculate skin-fold measurements properly.
After you know your body-fat percentage, you can calculate your fat weight and your lean weight, also called the fat-free mass. Thus, if your body-fat percentage is 25% and you weigh 150 pounds, your fat weight is .25 × 150 = 37.5 pounds, and your lean weight (or fat-free mass) is the difference, or 112.5 pounds. So, if you are going on a weight-loss program and lose 25 pounds, and your follow-up body-fat percentage is 20%, you now have .20 × 125 = 25 pounds of fat, and 100 pounds of lean.
There is not one agreed-upon definition for ideal body-fat percentages, but there is a good review of this by the American College of Sports Medicine. Also, your body-fat percentage usually increases as you age. Therefore, we don’t expect you to have the same body-fat percentage when you turn 70 years old that you had when you were 20. Tables 5-2 and 5-3 show some sample body-fat percent ranges at different ages for men and women.
We can also estimate your health risk from your weight by doing measurements around your waist, your hips, and your neck.
To measure your waist circumference, you should wrap a tape measure around your body (above your hip bone and below your rib cage). A measurement of 35 inches or greater is considered unhealthy for women. For men, a measurement of 40 inches or more is considered unhealthy.
To measure around your hips, wrap a tape measure at the widest part of your buttocks or hip. Then, calculate your waist-to-hip ratio (WHR) by dividing your waist measurement by your hip measurement. For women, a ratio of more than 0.8 is considered at higher risk, and for men, it is more than 1.0, because there is more abdominal fat.
To calculate your neck circumference, simply wrap a tape measure around your neck (not too tight! Be sure that you can breathe comfortably!) A measurement of 16 inches or more in women, or 17 inches or more in men is a risk factor for sleep apnea. Sleep apnea is a condition in which the airway can close intermittently at night resulting in poor oxygen flow to the brain. It is a risk factor, and a contributor to obesity. If you have an elevated neck circumference
and/or symptoms of sleep apnea (like morning fatigue, morning headache, snoring, or excessive daytime sleepiness), be sure to talk to your doctor about screening for sleep apnea.
How Can Factors That Contribute to Obesity Be Categorized?
Contributors to Developing Obesity
People gain weight for a wide variety of reasons (medical, psychological, physical, and functional).
It’s far more complicated than the age-old “calories in/calories out” mantra would suggest. In fact, we know that most of the risk for developing obesity is genetic. We know that if a child has a parent with overweight, they have a 40% increased risk for becoming overweight themselves. If both parents have overweight or obesity, this risk is 80%. Although there are some single-gene mutations that can cause severe obesity, for most of us, there are hundreds if not thousands of different genes involved in body-weight regulation. Given the proper environment, some people are very likely to develop obesity, whereas others aren’t. Have you ever noticed that some people can eat whatever they want and not gain weight, whereas others, despite carefully monitoring everything they eat, become quite heavy?
If we think about genetics “loading the gun” to develop obesity, the environment “pulls the trigger.” A person with a high genetic risk for developing obesity can be at higher risk if they live in a big city where they have a high- stress job that requires sitting most of the day, and struggle to make ends meet (as opposed to. . .if they won the lottery, lived in a tropical paradise, and became a yoga instructor).
Our American environment makes maintaining a normal body weight increasingly difficult. Our food supply is abundant, and we are exposed to an ever-increasing array of delicious but unhealthy foods. We are eating more sugar than ever. The average American is estimated to consume between 150 and 170 pounds of refined sugar every year! 100 years ago, the average consumption was just 4 pounds per year. We rely on cars and public transportation to get around; and since the advent of the personal computer and with the widespread use of the internet, we have become largely sedentary at work.
Medical Contributors to Obesity
Medical contributors to obesity include other diseases, like diabetes and sleep apnea. These diseases can directly cause obesity. Conversely, obesity can directly cause these diseases. Typically, as one condition becomes worse, so does the other. Fortunately, with weight loss, many of these diseases can improve, too. In fact, studies have shown that losing 6% of your body weight can reduce your risk of developing type 2 diabetes by roughly 60%. In addition to other diseases that directly cause weight gain, many prescription medications can also induce weight gain. These drugs include those used for diabetes, high blood pressure, contraception, depression and bipolar disorders, inflammation, seizures, and even insomnia.
Obesity has also been associated with many types of cancer, including cancer of the breast, ovary, uterus, stomach, pancreas, gallbladder, and even prostate.
Psychological Contributors to Obesity
Psychological contributors to obesity include diseases like depression and binge- eating disorder. We all eat for “emotional” reasons. We eat because it helps us feel better. We eat because we are stressed, anxious, happy, or fatigued. We eat in front of the television and consume more food than when we are focused on a task—or the so called “mindless eating.” We skip meals all day at work and then can’t stop eating at night. Or, we eat as part of our job when meeting with clients. Whatever the reason, food plays an important role in our personal lives and in our psychological health.
Physical and Functional Contributors to Obesity
Physical and functional contributors to obesity include things like joint pain and fatigue. These types of conditions can make it difficult to exercise or difficult just to get around. They affect our ability to do the things we’d like to do and decrease our quality of life. In fact, a recent study found that more than 200 diseases are related to obesity (Yuen M, et al, 2016).