April 22, 2009

Participants sought for nutrition-genetics study

by K.C. Jaehnig

CARBONDALE, Ill. -- Could slavery have reprogrammed some genes to make African-Americans heavier and predispose them to obesity-related diseases? Do genes or environment determine a taste for particular foods? A Southern Illinois University Carbondale student is looking for Africans and African-Americans to help her find out.

“If we can answer some of the genetic questions as to how our history affects the epidemic of Type II diabetes and obesity, we can tweak our approach in addressing it,” said Catrina Johnson, who is studying the relationship between nutrition and genetics as part of her graduate research in SIUC’s College of Agricultural Sciences. She is recruiting participants for a study, partially supported by the vice chancellor for research, that will correlate DNA data with physical measurements and survey information.

There’s no question about the devastating statistics. Using figures from 2000, the American Obesity Association rated 39.9 percent of African-Americans obese, based on a common height-to-weight relationship known as the body mass index, or BMI. The same calculations put the obesity rate among Mexican-Americans at 28.4 percent and among whites at 28.7 percent. The association also reported that diabetes affected between 16 and 26 percent of black and Hispanic Americans between the ages of 45 and 74 but only 12 percent of whites in the same age bracket.

“These are alarming statistics, but maybe it’s not just that we’re eating too many cupcakes -- maybe there’s a larger narrative there,” Johnson said.

With the end of the African slave trade, slave owners had to find a new source of slaves and so began “breeding” those they already owned. Many of the slaves produced were large (size being equated with strength) and able to get by on little food. Because they worked with a relatively small “breeding” population, genetic change -- in this case, a tendency toward heft and a slow metabolism -- could occur in just a few generations. This may account, in part, for the obesity “epidemic” in today’s African-Americans -- they’re simply different from whites.

“Greater lean body mass in African-Americans combined with other ethnic variations, such as bone density, results in a comparatively greater BMI,” Johnson said.

Nonetheless, blacks do suffer higher rates of obesity-related conditions, such as heart disease, high blood pressure and diabetes, than do whites. A branch of science known as epigenetics, which suggests that environmental conditions can change how genes operate and that these changes can be inherited, may further explain why.

As an example, Johnson pointed to a study of people born during World War II to Dutch women suffering from a famine caused by a German blockade. Many later became obese and developed diabetes as well as a host of other health problems. Scientists have proposed that conditions in a uterus where nutrients were in short supply may have altered fetal DNA to create a metabolism that burned calories slowly to make up for that lack.

Food choices also play a significant role in obesity and disease. Here, Johnson noted that diabetes afflicts half of Arizona’s Pima Indians, and most of those who have the disease are overweight. The Pimas’ problems with obesity and its related diseases began with their placement on reservations, then accelerated as, along with the rest of the country, they began eating less starch and fiber and more fat and sugar. Federal researchers have found that Pimas in Mexico’s remote mountains, who have managed to maintain much of their culture, are generally thinner, and less than 10 percent of them have diabetes.

“To the extent people can maintain traditional diets, they will stay healthy,” Johnson said.

But what if genetics influence your food choices? According to the National Institutes of Health, as many as 75 percent of African-Americans can’t digest lactose, a major ingredient in dairy products. Johnson, herself lactose-intolerant, assumed all blacks shared that trait until she met a Masai woman who, along with all the Masai people she knows, has no problem drinking milk.

“You can see a gene was lost somewhere in transition,” Johnson said. “I hope to show as part of this study where food preferences emanate from.”

Johnson is looking for African-Americans (both parents must be black), naturalized Africans who have lived in the United States for at least 10 years and Africans from the continent’s interior countries who are not citizens and who have lived in this country for less than 10 years. She will calculate their body mass, collect their DNA through simple cheek swabs and have them fill out questionnaires about their food choices. Working under the supervision of biotechnologist David A. Lightfoot at SIUC’s DNA Sequencing and Genomics Facility, she then will look for correlations between genes associated with metabolic efficiency, obesity and sensory perception and the data she has collected.

Participants will receive free Type II diabetes screenings and $80. Contact Johnson by e-mail at johncat1@siu.edu or by phone at 618/453-7678 for more information.