A study by researchers at the University of Arizona Mel and Enid Zuckerman College of Public Health finds that African American men with a high degree of West African genetic ancestry have a lower risk of obesity.

The obesity epidemic affects women and men of every ethnic group in the United States. A study by researchers at the University of Arizona Mel and Enid Zuckerman College of Public Health finds that African American men with a high degree of West African genetic ancestry have a relatively lower risk of being overweight, obese and diabetic. New research in the journal Frontiers in Genetics suggests that the cause may be partly genetic.

“We found that West-African genetic ancestry may afford protection against central adiposity in African American men, but not in African American women,” says the study’s lead author, Yann Klimentidis, PhD, an assistant professor who studies genetic epidemiology at the UA Mel and Enid Zuckerman College of Public Health.

Central adiposity (“belly fat”), the build-up of excess fat under the skin of the lower torso and around the internal organs, is a strong risk factor for obesity and diabetes, as well as for high blood pressure, high blood sugar, disease of the heart, liver, and pancreas, and some cancers.

Although socioeconomic factors, access to health care, healthy food and safe places to exercise, have been associated with obesity and other racial disparities in health, black and white men do not have significantly different rates of obesity according to the CDC.

Dr. Klimentidis and colleagues analyzed genetic data from 4,425 volunteers, all healthy African American women and men between the ages of 45 and 85. These data had been collected in the course of two prospective studies sponsored by the National Heart Lung and Blood Institute of the NIH: the Atherosclerosis Risk in Communities Study (ARIC) and the Multi-Ethnic Study of Atherosclerosis (MESA).

The investigators focused on approximately 3,500 nucleotides (“letters” in the genome) that often differ between people from West Africa and Europe. In this way, they could estimate the degree of West African genetic ancestry – the fraction of the genome inherited from West African ancestors – for each participant in the study. Previous research has shown that this fraction varies considerably among African Americans, due to differences in genetic contributions from ancestors from other ethnic groups, especially Europeans and Native Americans.

The results show that the Waist Circumference and Waist-Hip Ratio tends to be lower in African American men with a high degree of West African genetic ancestry, indicating that they have less central adiposity than African American men with a lower degree of West African genetic ancestry. In contrast, there was no association between Waist Circumference and Waist-Hip Ratio and the degree of West African genetic ancestry in African American women.

The researchers conclude that the gene pool of the African American population contains one or more gene variants – originally inherited from West African ancestors -- that give partial protection against central adiposity, but only when present in men. Further research is needed to identify these gene variants and the physiological mechanisms through which they operate, to help prevent and treat central obesity.

“There are still many unanswered questions, including: What are the specific genes that afford protection against central adiposity in men of West African ancestry, or conversely, What are the genes that predispose individuals of other ancestries to greater central adiposity? What cultural, socio-economic, or other factors might explain the lack of protection in African American women?” says Dr. Klimentidis.

“The reasons for group differences in multifactorial traits like obesity remain difficult to understand, especially when simplistic explanations do not easily explain complex patterns, like group differences which are not constant across sexes. We believe these new analyses begin to shed light on the factors underpinning some ethnic disparities in obesity,” says David Allison, distinguished professor of public health and director of the Nutrition Obesity Research Center at the University of Alabama at Birmingham, a co-author on the study.

The genetic contribution of West-African ancestry to protection against central obesity in African-American men but not women: results from the ARIC and MESA studies.
Frontiers in Genetics, June 1, 2016
http://journal.frontiersin.org/article/10.3389/fgene.2016.00089/full