Iowa State Researchers Study Relationship Between Obesity and Hormone That Stimulates Food Intake

Obesity is a major health concern for both adults and children. Researchers at Iowa State University are exploring the interaction between diet and appetite-related hormones, plus the effect that interaction might have on obesity. Michelle Bohan of LeMars is a graduate student in biochemistry. She's working with Donald Beitz, a distinguished professor of animal science and biochemistry, biophysics and molecular biology, on the project. Lloyd Anderson and Allen Trenkle, distinguished professors of animal science, are collaborating scientists. "Ghrelin is a recently discovered hormone that has been shown to stimulate food intake," Bohan said. "Our goal is to further understand the effect of diet composition on plasma ghrelin concentration and the effect of ghrelin on body composition." To that end, the researchers are comparing the differences in ghrelin concentration in lean and overweight humans. They also are comparing how two diets - Atkins and American Heart Association (AHA) - affect ghrelin concentration and other related hormones associated with food intake and body composition. In January 2005, eight female students ate three meals a day for four weeks in the dining area of the Human Metabolic Unit in LeBaron Hall. Eight men did the same thing this spring. During both feeding trials, two normal and two overweight participants were assigned to the Atkins diet. The Atkins diet contained 10 percent of calories as carbohydrate, 45 percent as protein and 45 percent as lipid. Two normal and two overweight subjects were assigned to the American Heart Association (AHA) diet that contained 63 percent of calories as carbohydrate, 12 percent as protein and 25 percent as lipid. Each diet was fed for 14 days before the participants switched to the other diet. On days 6 and 20, blood was taken from each participant at one hour before and one hour after the noon meal. Blood also was taken every hour from 7 a.m. to 9 p.m. on days 13 and 27. On days 14 and 28, the participants fasted from 7 a.m. until noon. On these two days, blood samples were taken at 11 a.m. and again one hour after the noon meal. Laboratory analysis of the blood samples showed hormone concentrations did respond differently to diet, body weight, time of day and other variables. Women consuming the Atkins diet tended to have lower fasting ghrelin concentrations than women did consuming the AHA diet. But ghrelin concentrations were not significantly lower one hour before lunch in women fed the Atkins diet than women fed the AHA diet unless they had been fasting. Bohan still is reviewing the data related to the female participants. Based on some preliminary analysis, she presented a poster of her results at a scientific meeting in San Francisco in April and drew this conclusion. "Dietary composition did not significantly alter ghrelin concentrations in either the normal or overweight women," Bohan said. "So, this study supports the hypothesis that ghrelin is controlled by caloric content, rather than the concentrations of proteins, carbohydrates and fats in the diet." Laboratory analysis of blood samples taken from the male participants will continue for several more months before final reports are developed. Funding for this research comes from a U.S. Department of Agriculture Special Research Grant to Iowa State's Center for Designing Foods to Improve Nutrition.