Viva La Familia
Hispanic Childhood Obesity Studied at Children's Nutrition Research Center

In a five-year study, the USDA/ARS Children's Nutrition Research Center at Baylor College of Medicine, in collaboration with the Southwest Foundation for Biomedical Research, is investigating childhood-onset obesity within the Hispanic population, which until now, has never been studied.

Childhood obesity is more prevalent among Hispanic children than children from other ethnic groups, and the United States problem has been steadily increasing over the past 10 years.

The study's purpose is to identify both genetic and environmental factors which make some children more prone to excess weight gain.

Dr. Nancy Butte, associate professor of pediatric nutrition at Baylor College of Medicine, is the study's principal investigator.

"We have elected to focus on Hispanic children for two reasons. It's not that we think the genes will be particularly unique to the Hispanic population, but because the incidence of childhood obesity is one of the highest among the Hispanic kids," she said. "The other reason is that the Hispanic population traditionally has large families."

Dr. Butte said most of the subjects are originally from Mexico, but are not eating a traditional Mexican diet, which consists of rice, beans, corn tortillas, and lots of vegetables and fruits. So far, researchers have seen a very high-fat diet - Kentucky Fried Chicken, McDonald's, and the like.

The study is looking for 300 Hispanic families to participate. All families must be currently living in Houston, have at least three children, and the children must be between the ages of 4 and 18.

Dr. Butte said obesity has a very large genetic component, and that there have been many traditional genetic studies done to prove that fact.

"We know that the problem is genetic - what we debate is what percent is genetic. You have to account for the environmental factor that is thrown into the mix," Dr. Butte said.

She said many researchers believe these genes, when put in a conducive environment, make some people more susceptible to developing obesity.

"You have to be in a positive energy balance to gain weight. You have to eat more than what you're burning off. For example, in a famine situation, no matter what genes you have, you're not going to be obese."

Dr. Carlos Bacino, assistant professor in the Molecular and Human Genetic Clinical Program at Baylor and one of the study's co-investigators, said obesity, as opposed to cystic fibrosis or sickle cell disease where the only factor is a single-gene abnormality, is more challenging because of the genetic and environmental factors, and because it is not one gene in particular that is causing the problem.

"Because of the availability of different tools, we have better ways to look at the genome in situations like obesity, hypertension and diabetes, where you have similar problems and strong genetic components, but the problems result not from genes alone but from the interaction of many genes with environmental factors," said Dr. Bacino.

"It is also very interesting that we know there are some single-gene mutations that cause very massive obesity," said Dr. Butte, "but they are very rare. What we're trying to understand in this population is what we call common obesity - it's not caused by one single mutation."

Dr. Butte explained that the "complex genes" involved in the search have not yet been identified. Instead, many investigators have gone after "candidate genes" - genes that might be good candidates for obesity.

"In this project, we're taking a different approach. We're going in blinded, and we're going to look at all the chromosomes for what we call "linkage" - types of genetic similarities within a family," Dr. Butte said.

The study investigators are interested in looking at a wide spectrum of body sizes and body fats.

"We're not just looking for obese kids. In all the families that we recruit, it is the variations that we see that will be the key to finding linkage," Dr. Butte said.

"We are looking for coincidences and differences among genetic materials from within a family and will compare those findings with other families," said Dr. Bacino. "When examining these factors closely, they may turn out to have some important similarities."

Study investigators will obtain several measurements from program participants. These include body composition, where the amount of lean tissue and body fat is measured using Dual Energy X-ray Absorptiometry, a painless procedure where the patient is scanned from the head to the feet. Another test given is the exercise test, where the amount of oxygen used while walking on a treadmill will be measured to determine physical fitness.

Maurice Puyau, an exercise physiologist on the study team, said for every 1 liter of oxygen expended while exercising, approximately five calories are burned.

In addition to having their vital signs and diets assessed, participants will also spend 24 hours in a calorimeter - a sealed room where oxygen uptake and carbon dioxide output are monitored. It is similar to a small bedroom, and is equipped with a bed, desk, toilet, sink, television, videocassette recorder, radio, CD player and telephone. Although each subject is alone, he or she can see through a window and communicate with the staff, parents and siblings by intercom or telephone. Parents are invited to stay while their children are in the calorimeter. During the course of their stay, subjects will be asked to eat, exercise and sleep according to a schedule.

There are many ways to define the word "obese." Definitions vary from children, to adults, to different regions of the world. Recently, the Centers for Disease Control and Prevention released body-mass index charts to help define the term. A BMI measures the height-to-weight ratio. It is calculated by dividing weight in pounds by height in inches, divided by height in inches, and multiplying the total by 703. Fractions and ounces must be entered as decimal values. For example, the BMI for a 33 pound 4 ounce child who is 37 and five-eighths inches tall would be calculated this way: 33.25 pounds divided by 37.625 inches, divided by 37.625 inches, multiplied by 703. The result is a BMI of 16.5.

For an adult, a score of 25 to 29.9 is considered overweight and a score of 30 and above is obese. In children, the BMI score curves from 17 for a 4-year-old, to a score of 30 for an 18-year-old. The healthy weight BMI for adults was just recently lowered from 27 to 25. Approximately 50 percent of the U.S. population is now considered overweight.

"Although there are many chubby babies who lose their baby fat, a recent study showed that if you have an overweight infant and obese parents, that child has a higher risk of obesity," said Dr. Butte. "If you look at a preschool-aged child and their risk for obesity later in life, it may be a correlation of 0.3. In a school-aged child, that correlation could be 0.5, but an obese teenager's chance of becoming an obese adult is way up there."

Dr. Butte said finding gene linkage might offer the possibility of prevention. By identifying individuals who are at-risk, early intervention and treatment may take place.

"Obesity is a thief, she said. "Willpower is not a always an acceptable solution to the problem."

For those families interested in taking part in the study, call Marilyn Navarrete at (713) 798-7002.

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©2006 Texas Medical Center

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