Heli J. Roy | 3/18/2005 10:00:10 PM
Both obesity and being overweight have increased significantly in recent years, with nearly two-thirds of U.S. adults being one or the other. Whether this weight gain has resulted more from an increasing sedentary lifestyle or from less exercise is under debate, according to LSU AgCenter nutritionist Dr. Heli Roy.
"It is not clear if and how effective formal exercise training is for sedentary individuals to lose fat and weight," Roy says. Under the leadership of the LSU Pennington Biomedical Research Center, a consortium of five institutions around the country is examining that relationship in phase 3 of a three-part research project known as the Heritage Family Study. "Heritage" is an acronym for HEalth, RIsk factors, exercise Training And GEnetics.
Initiated in 1992, the study investigates individual responses to exercise in three areas:
Phase 1 was conducted from 1992 to 1997. During this phase, 744 healthy, sedentary subjects, 17-65 years old, were recruited, tested, exercise-trained in the laboratory under supervision with the same program for 20 weeks and re-tested. The subjects came from families of white descent with both parents and biological adult offspring and from families or pairs of first-degree relatives of black ancestry. Various metabolic parameters, such as blood pressure, glucose and insulin levels, hormones and dietary intakes were determined during this phase.
Phase 2 of the study was conducted from 1997 to 2001. During this phase, the data from the previous phase were analyzed, including molecular and genetic studies. These analyses provided information about diabetes and heart disease risk factor response to exercise and possible genetic involvement in response to exercise.
Phase 3 of the study is still on-going (from 2001 to 2004). The main focus of Phase 3 is to expand and refine the search for genes and mutations that affect cardio-respiratory response to endurance exercise and cardiovascular disease and type 2 diabetes risk factor response to regular exercise.
Of the 744 participants, 557 had complete data on body composition measurements such as weight, height, eight different skinfold measurements, body fat percent and body density. After 20 weeks of intensive exercise training, there was a small, but significant decrease in skinfold measurements, body weight, fat mass and percent body fat. There was also a decrease in abdominal visceral fat, an important reduction from a health perspective.
Increased amount of abdominal visceral fat is an independent risk factor for diabetes and heart disease and reduction in abdominal fat obtained by diet and or exercise can result in improved cardiovascular profile.
Weight and fat losses were less than expected in this study, Roy says.
"This and supporting research suggest that exercise is not in itself good for inducing weight loss, but is very important in preventing further weight gain and maintaining reduced weight."
She explains that exercise is good in helping to maintain muscle mass during dieting. Individuals who have lost a lot of weight, such as those in the National Weight Control Registry, maintain their weight losses by eating low-energy, low-fat diets and engaging in regular physical activity.
"Exercise incorporated into an active lifestyle with sensible eating can lead to greater improvement in body fat content and weight over time," Roy says.
The research was funded by grants from the National Heart, Lung and Blood Institute of the National Institutes of Health of the U.S. government. Its stated goal is to investigate the possible genetic basis for the variability in the responses of physiological measures and risk factors for cardiovascular disease and type 2 diabetes mellitus to endurance exercise training.
The project is directed by Tuomo Rankinen of the Pennington Biomedical Research Center. The multicenter consortium was put together by Dr. Claude Bouchard, director of the Pennington Biomedical Research Center. Participating institutions include Indiana University, the University of Minnesota, Texas A&M University, Washington University and the LSU Pennington Biomedical Research Center.
For local information and educational programs in related areas of family and consumer sciences, contact an extension agent in your parish LSU AgCenter office.