Date

April 2009

Document Type

Thesis

Degree Name

M.S.

Institution

Oregon Health & Science University

Abstract

Persons following low carbohydrate (LC) diets often report a sense of “food disinterest”. Diets high in protein have also been shown to increase feelings of satiety after meal consumption compared to lower protein diets. Differences in the macronutrient composition of traditional low fat, low calorie and low carbohydrate diets may have different effects on the hormones that influence central regulation of appetite and energy balance. Consuming a diet that has a greater stimulatory affect upon hormones that induce short-term satiety should result in an increased feeling of fullness and a decreased feeling of hunger and lead to a decrease in energy intake. This study used a random order, crossover design to examine how acute exposure of 10 healthy, normal weight adults to low carbohydrate (LC) and high complex-carbohydrate (HC) meals affect circulating concentrations of weight regulation markers and influence hunger and fullness. Fasting and postprandial blood samples were collected over a period of 9.5 h and analyzed for concentrations of glucose, insulin, leptin, total and active ghrelin, GLP-1 and PYY. Participant feelings of hunger and fullness were assessed by visual analog scales (VAS) before and after meal consumption. Differences in AUC after the LC and HC meals were compared using one sided paired t-tests. Pattern of postprandial change in glucose, insulin, leptin, total ghrelin, GLP-1, and PYY concentrations over time were analyzed using orthogonal polynomials (up to order 4) with components of these polynomials assessed for significance using a Wilcoxon signed-rank test. Differences between concentrations for each analyte at pre-selected time points after LC and HC meal consumption were analyzed using repeated measures analysis of variance (MANOVA) and post-hoc analysis. Differences in linear contrasts between the LC and HC meals for VAS hunger and fullness scores were analyzed using a Wilcoxon signed-rank test. Total area under the curve for PYY (1107 ± 100 vs. 954 ± 72 pg·h/ml, p<0.05) and GLP-1 (55 ± 11 vs. 42 ± 9 pM·h/ml, p<0.01) was found to be higher after consumption of the LC meals than the HC meals, respectively. Total area under the curve was lower for glucose (793 ± 13 vs. 841 ± 20 mg·h/dL, p<0.05), insulin (84 ± 10 vs. 240 ± 23 μIU·h/ml, p<0.01)), and leptin (2.8 ± 0.58 vs. 3.7 ± 0.83 ng·h/kg fat mass·ml, p=0.04) after LC than HC meal consumption, respectively. There was no significant difference in total area under the curve after consumption of the LC meals than the HC meals for total (7662 ± 1746 vs. 7391 ± 1517 pg·h/ml, p>0.05) and active ghrelin (815 ± 199 vs. 865 ± 235 pg·h/ml, p>0.05), respectively. Repeated measures ANOVA showed a significant effect of diet for at least one of the selected time points for glucose, insulin, leptin, total ghrelin, and GLP-1 (p<0.05 for all significant time points). Repeated measures ANOVA was not significant for differences between LC and HC meals for active ghrelin and PYY at any of the time points selected. Postprandial patterns of change were significant for differences after consumption of LC compared to HC meals for all analytes. There were no significant differences any of the contrasts made between participant feelings of hunger and satiety after consumption of LC and HC meals. This study provided convincing evidence that there is a significant difference in the effect that consumption of LC meals has on the postprandial excursion of weight regulation markers compared to HC meals in healthy, normal weight individuals. The feelings of food disinterest and the resulting weight loss experienced by persons following LC diets may be related in part to changes in weight regulation hormones that affect the desire to consume food and feelings of fullness. This study used a random order, crossover design to examine how acute exposure of individuals with a normal body mass index (BMI) (18-25 kg/m2) to low carbohydrate (LC) and high complex-carbohydrate (HC) meals affect circulating concentrations of hormones known to affect central regulation of body weight (insulin, leptin, total and active ghrelin, PYY, and GLP-1), and influence hunger and satiety. Investigating the hormonal response of normal weight persons to each meal type will lead to an effective model that can be applied to understanding how these diets affect short term and long term weight regulation in overweight and obese individuals.

Identifier

doi:10.6083/M4KW5D0X

Division

Graduate Programs in Human Nutrition

School

School of Medicine

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