May 2015 Issue

Overweight/Obesity: Can Clients Be Fat But Fit?
By David Yeager
Today's Dietitian
Vol. 17 No. 5 P. 12

Here's a review of the research and what RDs can do to spur obese patients to better health.

More than one-third of adults in the United States are obese, which is defined as having a BMI of 30 kg/m2 or greater.1 For the general population, obesity increases the risk of numerous diseases.2 Many of these illnesses are metabolic abnormalities, such as coronary heart disease, type 2 diabetes, hypertension, abnormal blood lipids, insulin resistance, and fatty liver disease.2,3

Despite the health risks associated with obesity, there's a subgroup of people who show no signs of metabolic abnormality and are considered metabolically healthy.4,5 For example, a 2011 study found that metabolically healthy obese individuals had a lower risk of heart failure than normal-weight people who were insulin resistant.6 Study results such as this have led people to question whether it's possible for some people to be both obese and healthy.

A 2013 study described certain characteristics of people who were both obese and metabolically healthy, such as a waist circumference of no more than 40 inches for men and 35 inches for women; normal blood pressure, cholesterol, and blood sugar levels; normal insulin sensitivity; and good physical fitness.5 Other studies, however, have found an increased risk of mortality in obese people, regardless of their metabolic health.7,8 So are obesity and health mutually exclusive?

"It depends on how you define healthy," says Samuel Klein, MD, the Danforth professor of medicine and nutritional science and director of Washington University School of Medicine in St. Louis' Center for Human Nutrition. "If you look at metabolic health as your definition of healthy, it is possible for people who are obese to be metabolically healthy."

However, that doesn't mean people should let their gym memberships lapse. From an overall health standpoint, Klein says, obesity is undesirable because it affects numerous organ systems. He adds that more rigid criteria for metabolic health may reveal slight metabolic abnormalities, such as mild insulin resistance.

Rather than focusing on whether it's possible to be both fat and fit, the more useful question is why some obese people don't show signs of metabolic abnormalities; Klein says about 15% of obese people will maintain metabolic health over 20 years. He believes that understanding the relationship between body fat and abnormal metabolic health potentially will allow medical practitioners to target the pathways that cause metabolic dysfunction.

Healthy vs Unhealthy Obesity
To study the differences between metabolically healthy and metabolically unhealthy obese people, Klein and his colleagues induced weight gain in two groups of individuals, one metabolically normal and the other metabolically abnormal. The study groups increased their caloric intake by eating fast food. Although calories increased, the nutrient distribution of carbohydrates, protein, and fat in their diets remained the same. In addition, a significant increase in carbohydrate content in both groups was due to beverages that were sweetened with sucrose or high fructose corn syrup. An important finding was that weight gain caused decreased insulin sensitivity and increased insulin secretion in the metabolically abnormal group, but had no effect on the metabolically normal group.4

There also was a difference in the adipose tissues of the two groups. Proteins and enzymes that aid lipid metabolism increased in the adipose tissues of the metabolically normal obese group.4 They didn't increase in the metabolically abnormal obese group.3 Klein says findings such as this can help researchers better understand why obesity causes illness in some people but not in others.
"It's very important to understand the underpinnings of metabolic dysfunction," Klein says. "Metabolic abnormalities are probably the most important complication of obesity because they're so tightly related with obesity and have such serious effects on quality of life and health. Understanding why obesity causes these problems in some people and not in others is really critical to understanding the pathogenesis of obesity."

Klein says there are several probable reasons why obesity leads to metabolic dysfunction. He and his colleagues are investigating the possible role that the composition of microbial colonies in the human digestive system plays in obesity. Recently, they completed a study of gut bacteria from obese people, but Klein says it will take time to analyze the data; there are about 1,000 different species of microbes in the human intestine. Although the effects of gut microbiota on metabolic health aren't yet known, Klein thinks this is a promising area of study.

In addition, Klein says food choices may play a role in metabolic health. He says people who eat more fruits and vegetables and fewer processed foods may be metabolically healthier than people who eat more snack foods and sugar-sweetened beverages. Physical activity and the amount of sleep a person gets also may influence metabolic health, he adds. Plus, genetic factors should be taken into account.

"Genetics is likely very important. Some people may inherit the ability to be metabolically healthy or unhealthy when they gain weight," Klein says. "Also, someone who's very physically active may maintain metabolic normality better than someone who's not physically active. So lifestyle, in terms of both food and activity, could influence whether you're metabolically healthy or not."

Advice for Dietitians
The extent to which lifestyle changes influence metabolic health requires more research, and because research findings sometimes can be difficult to translate into practical advice, people often look to nutrition professionals for answers. Although some obese people may remain metabolically healthy for long periods of time, most nutrition professionals still recommend that individuals strive for a BMI between 18 kg/m2 and 25 kg/m2. A study published in January found that nearly one-half of obese people who maintained metabolic health over 20 years eventually became metabolically unhealthy.9

Jessica Crandall, RDN, CDE, AFAA, a spokesperson for the Academy of Nutrition and Dietetics, says, in addition to lowering the risk of metabolic complications and other diseases, maintaining an optimum body weight reduces wear on the joints and improves cardiovascular health. Many people have difficulty shedding extra pounds, but Crandall says it's important to view health in the context of overall lifestyle, rather than simply focusing on a number; adopting healthier habits can influence more than weight. She says some changes people make may not be immediately measureable, but they can have a significant effect on overall health.

"For example, incorporating more fruits and veggies will assist you in meeting your fiber and antioxidant needs and make you feel more full. This habit may be beneficial in lowering your cholesterol and providing necessary nutrients to your cells for prevention of cancer, and the added fiber can assist you with lowering your risk of colon cancer," Crandall says. "This is just one example of how a healthful habit can be helpful to your health but may not change your weight."

Although it's easy for most people to gain 10 lbs in a decade, Crandall recommends that people make diet and exercise adjustments that will work for them, no matter how much they weigh. Focusing solely on weight can be self-defeating. Crandall says a balanced mental approach is important, and people should focus on the process of maintaining health, rather than the burden of losing weight.

"Weight loss is a challenge for many individuals, but starting with good behaviors and habits will help to lead the way to a healthier you," Crandall says. "Setting yourself up for success, mentally, I think is very important. Don't set the bar too high. If your total weight loss goal is 50 lbs, it may take you 20 weeks to get there. That's OK. At least you're progressing in the right direction."

— David Yeager is a freelance writer and editor in southeastern Pennsylvania.

1. Ogden CL, Carroll MD, Kit BK, Flegal KM. Prevalence of childhood and adult obesity in the United States, 2011-2102. JAMA. 2014;311(8):806-814.

2. National Institutes of Health: National Heart, Lung, and Blood Institute. Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: The Evidence Report. Published September 1998. Accessed March 13, 2015.

3. Fabbrini E, Sullivan S, Klein S. Obesity and nonalcoholic fatty liver disease: biochemical, metabolic, and clinical implications. Hepatology. 2010;51(2):679–689.

4. Fabbrini E, Yoshino J, Yoshino M, et al. Metabolically normal obese people are protected from adverse effects following weight gain. J Clin Invest. 2015;125(2):787-795.

5. Stefan N, Häring HU, Hu FB, Schulze MB. Metabolically healthy obesity: epidemiology, mechanisms, and clinical implications. Lancet Diabetes Endocrinol. 2013;1(2):152-162.

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8. Hinnouho GM, Czernichow S, Dugravot A, Batty GD, Kivimaki M, Singh-Manoux A. Metabolically healthy obesity and risk of mortality: does the definition of metabolic health matter? Diabetes Care. 2013;36(8):2294-2300.

9. Bell JA, Hamer M, Sabia S, Singh-Manoux A, Batty GD, Kivimaki M. The natural course of healthy obesity over 20 years. J Am Coll Cardiol. 2015;65(1):101-102.