Understanding Normal Weight Obesity

Even people with a normal weight, according to the BMI tables, can suffer from the fall out of obesity. Understand the health risks of normal weight obesity, and what you can do about it.

The baby boomer generation has experienced its fair share of obesity. Boomers have a high rate of obesity compared with previous generations; according to the Center for Disease Control (CDC) in 2018, the prevalence of obesity in people aged 60 and older was 41%. However, the prevalence in the age group 40-59 years old was even higher at 42.8%. So, if you are lucky enough to be in the “normal weight” category, does that mean you can breathe a big sigh of relief?

Normal Weight Obesity and BMI

Not so fast. Even people with a normal body mass index (BMI) can fall prey to a condition called normal weight obesity (NWO). It may sound like an oxymoron, but it’s a real health concern, according to a growing body of evidence. Obesity is an excess amount of body fat, and is classified by body mass index (BMI). It’s possible to fall into the normal weight range and still have weight-related health issues, says Francisco Lopez-Jimenez, MD, a Mayo Clinic cardiologist who is leading this field of research.

Research indicates that people should do more than monitor BMI to determine their health status; they should also monitor levels of body fat. While BMI is still considered a very helpful tool for evaluating weight status, it does have its limitations. For example, individuals who are very muscular (i.e., athletes) may have a falsely high BMI because the measurement does not account for increased weight due to muscle composition. It could also inaccurately portray weight status for individuals, like older people, who have lost muscle. And BMI does not take into account central adiposity, which has been associated with increased disease risk.

And now NWO is another reason to look beyond BMI. NWO is characterized as having a normal BMI with a large percentage of body fat—more than 30% for women and 20% for men.

Mayo Clinic researchers studied 2,127 normal weight adults, equally divided between men and women, relying on data from the Third National Health and Nutrition Examination Survey. They discovered that more than one half of the subjects had NWO. In fact, NWO is so prevalent that Lopez-Jimenez estimates up to 30 million Americans have the condition.

NWO Brings Health Risks

What’s the big deal about NWO? Unfortunately, this condition carries risks similar to overweight or obesity. Lopez-Jimenez explains that in NWO, people have little of the good stuff, such as muscle mass and dense bones, and too much of the bad stuff: body fat. He adds, “Elderly people who are normal weight are likely to have NWO as they have lower muscle mass and lighter bones.” People who are considered to have NWO are at higher risk for cardiovascular morbidity, insulin resistance, and dyslipidemia. A 2013 study revealed that NWO has a slight association with metabolic syndrome factors. The prevalence of metabolic syndrome was 3 times greater in men (3.1) than in women (.9). It was also reported that men had higher blood pressure and blood glucose, while women had low HDL-cholesterol. This also increased the risk of inflammation, cardiovascular disease, and metabolic syndrome.

Managing the Condition

What can you do about NWO and its accompanying risk factors? Lopez-Jimenez suggests that people in the normal weight range, particularly those who are sedentary or eat a suboptimal diet, be screened for body composition on a routine basis.

“It’s in the intermediate range—when you fall in the normal or mildly elevated BMI—that you should determine if you’re body fat is too high. It’s not necessary for everybody to measure their body fat to see if they have normal weight obesity. If someone is very skinny (below a BMI of 18.5), they don’t need to check body fat because their body fat is likely very low. And if someone is overweight—over 30 to 35 BMI—then we know that they already have high body fat,” says Lopez-Jimenez.

Unfortunately, assessing body fat percentage is not as simple as hopping on a scale. But there are some reliable methods for measuring it. Just steer clear of techniques that are either very accurate but impractical or very simple but unreliable. Lopez-Jimenez suggests the following two methods for measuring body fat composition—both reliable and practical:

• Bioelectric impedance or bioimpedance: Utilizing an electrical current to measure body composition levels, this method is becoming popular at clinics and fitness centers because of its ease of use and relative low cost. But people shouldn’t fall for home versions of bioimpedance machines sold in drug stores because they may not be accurate.
• BOD POD or air displacement: The BOD POD, a machine that looks like a plastic space capsule, uses air to displace body volume to evaluate body fat composition. Available in many locations (eg, hospitals, fitness centers), the BOD POD is very reliable and simple to use.

Once a professional has established the presence of NWO, treatment should focus on more than simply eating a balanced, healthful diet; this condition depends much more on exercise. In NWO, the goal is not to lose weight but to change body composition. Lopez-Jimenez says, “If you’re at normal weight and you lose more weight, you may not be changing your body fat percentage. You could be losing muscle, not fat.”

Lopez-Jimenez suggests a combination of aerobic exercise and strength or resistance training exercise in addition to a healthful diet to alter body fat composition—yet another reason to understand how critical exercise is at any age.

For other blogs on healthy weight, check out the following: 

11 Science-Based Weight Loss Tips
7 Vegan and Vegetarian Weight Loss Tips & Recipes
12 Nutritionists Tips for a Healthy Weight