Genetics and racism contribute to racial-ethnic disparities in obesity and comorbidities
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Obesity prevalence is on the rise across the U.S., but some groups are at a greater risk for the disease than others.
According to National Health and Nutrition Examination Survey data published by the National Center for Health Statistics, the prevalence of obesity increased overall from 30.5% in 1999-2000 to 42.4% in 2017-2018. However, according to age-adjusted data from 2017-2018, 49.6% of non-Hispanic Black adults and 44.8% of Hispanic adults had obesity compared with 42.2% of non-Hispanic white adults. Differences are even greater among women: 56.9% of non-Hispanic Black women and 43.7% of Hispanic women have obesity compared with 39.8% of non-Hispanic white women.
These disparities stem from a long history of racial discrimination and inequities in the U.S., according to Joshua J. Joseph, MD, MPH, FAHA, assistant professor of medicine in the division of endocrinology, diabetes and metabolism at The Ohio State University College of Medicine in Columbus.
“Many of those factors go back to the social determinants of health,” Joseph told Endocrine Today. “You can look directly at the 1936 residential security maps that looked at redlining. The same areas that had redlining in 1936 are the same areas that struggle with obesity now.”
Genetics also plays a role, according to Fatima Cody Stanford, MD, MPH, MPA, MBA, FAAP, FACP, FAHA, FAMWA, FTOS, an obesity medicine physician-scientist at Massachusetts General Hospital and Harvard Medical School and an Endocrine Today Editorial Board Member.
“There are a lot of genetic level studies that point to genetic differences at the molecular level that demonstrated the higher likelihood of having obesity if you are from a racial-ethnic minority group,” Stanford told Endocrine Today.
Simply looking at obesity prevalence can paint an imperfect picture. The National Center for Health Statistics data define obesity as a BMI of 30 kg/m2 or higher. On that definition, Asian adults have the lowest obesity prevalence among racial-ethnic groups at 17.4%. However, research has revealed that Asian adults have more significant risks for cardiometabolic consequences of overweight or obesity at a much lower BMI than other groups, leading WHO to lower the BMI cutoff for obesity in Asian populations to 27.5 kg/m2 in 2004.
“Different people from different regions of the world distribute body fat in different ways,” Jamy Ard, MD, FTOS, professor in the department of epidemiology and prevention at the Wake Forest School of Medicine and an Endocrine Today Editorial Board Member, said in an interview. “The distribution of body fat is probably most important in thinking about risk of disease. Individuals of Asian descent may not have a large volume of excess body fat, but the excess body fat they have gets distributed in the visceral adipose tissue. That fat is more deleterious to health, so even a smaller amount leads to worse health outcomes.”
These racial disparities in obesity are a multifactorial problem with no single solution, according to the experts. Interventions needed to reduce disparities include improving access to bariatric surgery and medical therapies and fixing systemic problems in underserved communities.
“To combat the epidemic of obesity everybody must focus more on minority communities, especially on Black, Hispanic and Native American communities, because they are the ones suffering the most,” Ricardo Correa, MD, EdD, FACE, FACP, CMQ, endocrinology fellowship program director and director for diversity in graduate medical education at the University of Arizona College of Medicine-Phoenix, Phoenix Veterans Affairs Medical Center, and health equity fellowship director for Creighton University School of Medicine-Phoenix, told Endocrine Today. “Addressing the societal determinants of health — systemic racism — can be one of the solutions for decreasing disparities in those communities.”
Genetics and fat distribution
Some factors affecting differences in obesity rates go beyond social and environmental, as researchers have found certain genetic markers are associated with odds of higher BMI.
A genome-wide association study published in Obesity in 2017, with 1,570 people from West Africa and replication in 9,020 Black U.S. residents, revealed Black adults with obesity had statistically significantly higher serum levels of the genetic variant SEMA4D compared with those without obesity. Adults with the variant had a higher prevalence of obesity (55.6% vs. 22.9%) and a higher mean BMI (31.9 kg/m2 vs. 26.62 kg/m2) than those without the variant.
Several studies have also examined polymorphisms in the brain-derived neurotrophic factor gene, which contributes to the regulation of food intake and body weight. In findings published in European Review for Medical and Pharmacological Sciences in 2021, the rs7934165 polymorphism, common among women from Mexico, was found more frequently in those with a high waist-to-hip ratio than those with a low waist-to-hip ratio (43.4% vs. 25.2%; P = .01).
Defining obesity among racial-ethnic groups by using a BMI benchmark of 30 kg/m2 can also be misleading. Researchers caution that cardiometabolic risks stemming from excess body fat can differ between racial-ethnic groups.
“There are two pieces of body composition,” Morgana Mongraw-Chaffin, PhD, MPH, FAHA, assistant professor in the department of epidemiology and prevention at Wake Forest School of Medicine, told Endocrine Today. “The subcutaneous fat, which is the fat right underneath the skin, is the part that is not impacting cardiometabolic risk. What’s impacting risk the most is visceral and ectopic fat, the fat that’s inside our body cavity and wrapped around and inside our organs. That’s what actually increases risk for type 2 diabetes and cardiovascular disease.”
Mongraw-Chaffin noted that people of Asian descent tend to have a higher amount of visceral fat compared with other racial-ethnic groups.
Researchers have found that BMI cutoff values below 30 kg/m2 are associated with cardiometabolic disease for several racial-ethnic groups. In data from a Canadian cohort published in 2011, an equivalent incidence rate for diabetes at a BMI of 30 kg/m2 among white adults was observed at 24 kg/m2 among South Asian, 25 kg/m2 among Chinese and 26 kg/m2 among Black adults. In a 2010 study that examined data from the Multi-Ethnic Study of Atherosclerosis, diabetes incidence rates were higher among Chinese, Hispanic and Black adults with a waist circumference in the 95th percentile compared with white adults.
In a letter published in Mayo Clinic Proceedings in 2019, Stanford and colleagues proposed new BMI cutoffs for white, Black and Hispanic adults created using NHANES data to estimate BMI distribution and how it related to risks for hypertension, dyslipidemia and diabetes. The proposed values lowered the mean BMI cutoff for Black and Hispanic men to 28 kg/m2 and for white men to 29 kg/m2. The overall BMI cutoff was also lowered to 29 kg/m2 for Hispanic women and 27 kg/m2 for white women. Black women were the only group to see a higher cutoff at 31 kg/m2.
“Looking at those criteria, we actually saw a shift such that the cutoff is typically 30 kg/m2 or above for obesity, but for Black women almost across the board, the criteria went from somewhere between 31 kg/m2 to 33 kg/m2,” Stanford said. “This shows how BMI criteria differ by gender and race and how adhering to strict numbers can sometimes be deleterious.”
Systemic racism, social determinants
Yet, genetics cannot fully account for obesity disparities in the U.S., according to Ard.
“We have to look at the social determinants of health being core to these differences,” Ard said. “Physiological differences don’t fully explain differences that we see in distribution of body weight or body size as measured by BMI. You have to look at some of these other factors that are fixed and represent different exposure to the obesogenic environment.”
Regardless of race and ethnicity, individuals who face a greater number of social determinants of health are more likely to have obesity. In a 2021 study published in Obesity, more than 161,000 U.S. adults were placed into quartiles based on social determinants of health. Those with the most hurdles had a 50% higher obesity prevalence than those in the lowest quartile. Furthermore, those with overweight and obesity were more likely to belong to a racial-ethnic minority group.
Systemic racism plays a role in the prevalence of obesity and other cardiometabolic diseases, according to Joseph. In 1934, the Federal Housing Administration began guaranteeing mortgages to promote homeownership during the Great Depression. As part of the program, residential maps were developed to indicate areas deemed safe to insure mortgages. The FHA mass-produced subdivisions in areas marked desirable for white Americans, as long as the homes were not sold to Black Americans. Areas where Black families lived were labeled as red, or hazardous for insuring mortgages.
The process, known as redlining, continues to cause disparities today, with more racial-ethnic minority people living in redlined neighborhoods compared with white individuals, and these neighborhoods face a larger burden of social determinants of health and higher rates of cardiometabolic diseases.
The social determinants of health people living in underserved communities face are numerous. One is the lack of available healthy foods, especially in neighborhoods without a grocery store nearby.
“If you live in a food desert where there are no stores for you to get healthy, nutritious foods, then it may be more difficult to do some of those things that ultimately lead to weight loss,” Joseph said. “That’s where it’s really important for health systems and practitioners to think through what some of those barriers and challenges are.”
An inability to engage in physical activity can also be a barrier.
“For people who live in a community with high crime, it’s not easy to tell them to go out and take a walk, because it’s risky,” said Correa, who is also an Endocrine Today Editorial Board Member. In addition, some people also struggle to fit healthy habits into their schedule due to working hours, child care considerations and more, according to Mongraw-Chaffin.
“A lot of it comes down to access to resources, whether its healthy food, food insecurity or food deserts, whether it’s safe and enjoyable places to exercise, access makes a big difference,” Mongraw-Chaffin said. “It also comes down to people’s access to time and ability to devote their energy and resources to those kind of healthy lifestyle behaviors.”
Health care access is another major barrier. Correa noted that if a person with obesity has no easy access to a primary care physician due to the lack of a clinic in the community, an inability to pay or lack of transportation, they will not receive the care they need.
Access to obesity treatment is an issue for all Americans, with only about 1% of those with obesity in the U.S. utilizing bariatric surgery or obesity medication. Ard noted there are some racial disparities with obesity treatment as well, as utilization rates among Black patients are similar to those in the general population, despite the higher prevalence of obesity among Black adults.
Bariatric surgery rates differ between white and other racial-ethnic groups with obesity, although not because of a lack of willingness from the patient’s perspective. In a 2019 study published in Surgery for Obesity and Related Diseases, white youths aged 12 to 19 years with obesity underwent bariatric surgery more often than Black and Hispanic youths, despite lower obesity prevalence among white patients. However, another study published in 2015 in Surgical Endoscopy found that Black and Hispanic people with obesity are just as likely to proceed with bariatric surgery compared with white people.
“Persons that were racial and ethnic minorities were less likely to be referred for obesity, but when referred, they were just as likely to go for surgery,” Stanford said.
Individualizing treatment
Devising an individualized treatment strategy goes beyond skin color, according to Correa. Providers must understand the culture of each patient, he said, noting that there may be differences between a Hispanic community made up of people with a Puerto Rican background and another of people with Mexican heritage.
Stanford said she does not give any patient a specific target BMI.
“I don’t think strategies go by ethnicity, it’s individual,” Stanford said. “When we’re looking at things like BMI or looking at populations, we can make conjectures about a population at large. But when I’m working with each individual patient, I want to get them to the happiest, healthiest weight for them.”
Ard said providers must consider the full picture when devising an obesity treatment plan, noting that people facing a greater number of social determinants of health may have a more difficult time losing weight. A treatment plan individualized for a person’s living environment and tailored to be culturally appropriate may lead to greater success.
“Some people are having to fight against more of an obesogenic environment, and some people are having to fight against less of that,” Ard said. “A lot of that is determined by social status in life and other factors that have historically segregated based on racial categories within the U.S.”
Mongraw-Chaffin said devising an individual treatment plan includes assessing cultural background and community resources.
“The underlying relationships for treatment are the same, but in practice, some patients will have more of a need for connection to resources,” Mongraw-Chaffin said. “Some patients will have a need for low or no-cost resources, and many patients will have different preferences for different types of resources. Connection to resources that may be culturally appropriate and acceptable for those individual patients is really key.”
Public policy changes needed
The changes needed to close disparities in obesity treatment are multifaceted. With uptake in obesity medications and bariatric surgery low across the board, health care professionals are advocating for legislation such as the Treat and Reduce Obesity Act to expand Medicare access for anti-obesity medications and intensive behavioral therapy.
“We need to improve access to care and access to evidence-based treatments and have those be covered by health insurance,” Ard said. “The federal government needs to change in terms of improving access to treatment with Medicare. Medicare doesn’t cover anti-obesity medications currently, and that’s the biggest health insurance program in the country. A lot of African Americans rely on Medicare in their older years to get coverage for treatment, so that’s a large group of people that have no access to more intensive treatment that should be available. Those types of systemic changes need to be addressed to really see movement regarding disparities.”
Joseph said interventions to improve the health environment could have an impact on obesity disparities. In a 2011 study, a cohort of 4,498 women with children living in public housing were randomly assigned to a housing voucher to move to a low-poverty census tract, an unrestricted voucher with no special counseling on moving, or a control group with no voucher. After more than a decade of follow-up, the low-poverty voucher group had fewer participants with obesity compared with controls.
“If you can improve the environment in which individuals live, then you can lower the rates of chronic diseases like obesity,” Joseph said.
Mongraw-Chaffin said obesity treatment and prevention should be tailored toward families. If two people in a family have overweight or obesity, but only one person attempts to lose weight, that person is less likely to be successful than if both people attempted to lose weight.
“We’re looking at 60% of the population in the U.S. having overweight or obesity,” Mongraw-Chaffin said. “That is not an individual problem, and it doesn’t have individual solutions that are going to be successful when everyone is in this obesogenic context. We really need a public health approach to make the healthiest option the easiest option.”
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- For more information:
- Jamy Ard, MD, FTOS, can be reached at jard@wakehealth.edu; Twitter: @drard
- Ricardo Correa, MD, EdD, FACE, FACP, CMQ, can be reached at riccorrea20@gmail.com; Twitter: @drricardocorrea.
- Joshua J. Joseph, MD, MPH, FAHA, can be reached at joshua.joseph@osumc.edu.
- Morgana Mongraw-Chaffin, PhD, MPH, FAHA, can be reached at mmongraw@wakehealth.edu.
- Fatima Cody Stanford, MD, MPH, MPA, MBA, FAAP, FACP, FAHA, FAMWA, FTOS, can be reached at fstanford@mgh.harvard.edu.
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