What’s New in Understanding the Risk Associated With Body Size and Shape?Pears, Apples, and Olives on Toothpicks

Sun et al¹ discussed the importance of what they call normal-weight central obesity based on data from the Women’s Health Initiative (WHI). They found that, regardless of body mass index (BMI), postmenopausal women with normal-weight central obesity, reflected by high waist circumference (WC) and low BMI, are associated with a higher risk of all-cause mortality compared with women with normal weight and no central obesity.¹ Moreover, normal-weight central obesity was associated with a higher risk of cause-specific mortality, such as mortality from cardiovascular disease and cancer.¹ The study by Sun et al¹ is among few studies looking at the association of BMI with WC for individuals with normal weight.

There are several important aspects to the study by Sun et al.¹ First, it is a reminder that the scale is not everything. We all intuitively know that BMI, which is calculated as weight in kilograms divided by height in meters squared, is a function of total mass and not just fat mass, but we may be mistaken into thinking that those with low BMI are ipso facto fit and at low risk. Furthermore, the article by Sun et al¹ highlights not only that factors such as cardiovascular fitness, lean muscle mass, or metabolic indicators (such as various hormones and metabolites) provide important additional information about risk but also that simple anatomic distribution may be predictive.

Despite such interesting conclusions, the study by Sun et al¹ has limitations. It only includes postmenopausal women and, therefore, may not be generalizable to men or younger women, an issue that is well addressed by the authors. Moreover, it is worth remembering that such studies demonstrate association, which may or may not be indicative of causation.

This study and prior literature suggest that a healthy standard in women based on body shape may entail a narrow abdominal area above a wider gluteofemoral area, similar to a pear shape. The opposite of this body type is the so-called apple shape, where the accumulation of fat is concentrated in the abdominal area. Likewise, the accumulation of fat in the upper part of the body on an otherwise thin figure—a body type that might be labeled an olive on a toothpick—may be deleterious. Yet, with all of these observations, the identification of a body shape associated with higher risk does not necessarily imply that body shape is malleable or that, if body shape were modified, it would causally affect risk. Such conclusions require other designs and data for evaluation.

Considering WC along with BMI in association with health and longevity goes beyond simply treating all mass in the body as a homogenous pool. By incorporating a simple measurement that entails circumference (or, more aptly, perimeter) and, by implication, area or volume of tissue, such associations may show more predictive power. Nevertheless, although including WC may be a refinement over BMI alone in some contexts, WC still remains something of a black-box predictor of an outcome as opposed to a mechanistic or physiological explanatory factor.

Waist circumference is certainly a notable factor when studying obesity; however, this is not a new finding. As far back as 1947, French physician Jean Vague,² MD, suggested that obesity in the upper half of the body was associated with cardiovascular disease and diabetes, an association he did not find in individuals with more fat in the lower half of the body. In 1995, Sjöström et al³ studied the association of visceral obesity with cardiovascular risk factors. Following these findings, Elobeid et al⁴ examined the association of BMI with WC by sex and race subgroups from the US population and investigated its secular increase since 1959 in the United States. They found that increases in WC were higher than would be expected solely from increases in BMI, suggesting an overall change—and not a salubrious one—in body fat distribution for the US population.⁴

In the clinical realm, the challenge of considering WC was approached by Klein et al.⁵ On the one hand, Klein et al⁵ concluded that WC provides an indication of body fat distribution, which can be valuable. However, on the other hand, the practical use of WC in the clinical setting seemed to have little value when BMI was already considered. Nevertheless, Klein et al⁵ also stated that measuring WC could provide additional information in some settings, for example, because aerobic exercises can cause reductions in both WC and cardiovascular risk without necessarily modifying BMI.

In that regard, the World Health Organization offered an expert consultation⁶ in 2008 as a response to the obesity problem and associated chronic diseases, in particular for low- and middle-income countries. The organization drew attention to the importance of central obesity, which was associated with an increased risk of myocardial infarction, stroke, and premature death, which were not associated with BMI. The report’s aim was to create guidelines for the effective use of specific cutoff points for WC and waist-to-hip ratio. This study detected variations in the cutoff points that assess the association of disease risk with measures of abdominal obesity by ethnicity and age.⁶ Although the current recommended cutoff points for WC as a risk indicator are treated as largely universal, there may be value in further work to refine cutoffs that vary by age, sex, and ethnicity.

In 2010, there was an analysis of the Cancer Prevention Study II Nutrition Cohort,⁷ which included men and women. The investigators drew a similar conclusion that emphasized “the importance of WC as a risk factor for mortality in older adults,”⁷ regardless of whether BMI was categorized as normal, overweight, or obese. Their results suggested that “regardless of weight, avoiding gains in WC may reduce risk of premature mortality.”⁷

In summary, central obesity has repeatedly been proven as a strong factor for the higher risk of morbidity and mortality associated with obesity. The analysis done by Sun et al¹ is relevant since it shows that, even for women with normal BMI, central obesity can potentially lead to a higher risk of all-cause and cause-specific mortality. This suggests a more nuanced understanding and communication of obesity risk.

Published: July 24, 2019. doi:10.1001/jamanetworkopen.2019.7336

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2019 Golzarri-Arroyo L et al. JAMA Network Open.

Corresponding Author: David B. Allison, PhD, School of Public Health, Department of Epidemiology and Biostatistics, Indiana University Bloomington, 1025 E Seventh St, PH 111, Bloomington, IN 47405 (allison@iu.edu).

Conflict of Interest Disclosures: Dr Allison reported a patent to US 20130261470A1 pending; receiving grants from the National Institutes of Health; receiving personal payments or promises for same from the American Society for Nutrition, American Statistical Association, Biofortis Research, Columbia University, Fish & Richardson, Frontiers Publishing, Henry Stewart Talks, IKEA, Indiana University, the Laura and John Arnold Foundation, Johns Hopkins University, the Law Offices of Ronald Marron, MD Anderson Cancer Center, Medical College of Wisconsin, the National Institutes of Health, Sage Publishing, the Obesity Society, Tomasik Kotin Kasserman LLC, University of Alabama at Birmingham, University of Miami, Nestlé, and WW International (formerly Weight Watchers International); donations being made on his behalf by the Northarvest Bean Growers Association; serving as an unpaid member of the International Life Sciences Institute North America Board of Trustees; that his current institution, Indiana University, has received funds to support his research or educational activities from the National Institutes of Health, the Alliance for Potato Research and Education, American Federation for Aging Research, Dairy Management, Herbalife Nutrition, the Laura and John Arnold Foundation, and Oxford University Press; and that his former institution, the University of Alabama at Birmingham, received gifts, contracts, and grants from the Coca-Cola Company, Pepsi, and Dr Pepper Snapple Group. No other disclosures were reported.