All ETDs from UAB

Advisory Committee Chair

Barbara A Gower

Advisory Committee Members

Timothy M Beasley

David A Calhoun

Gary R Hunter

Julie L Locher

Bradley R Newcomer

Document Type

Dissertation

Date of Award

2012

Degree Name by School

Doctor of Philosophy (PhD) School of Health Professions

Abstract

Ghrelin is a hormone known to stimulate appetite and food intake. Although certain macronutrients differentially suppress ghrelin on an acute basis, it is unknown whether habitual macronutrient intake affects circulating ghrelin. Thus, the first experimental aim was to determine whether 8-week habituation to diets differing in carbohydrate or fat would affect fasting ghrelin or ghrelin response to a mixed meal. Recent reports also suggest that ghrelin regulation may relate to propensity for obesity. Obesity is more prevalent among AA compared to EA, with the highest rates among AA females. This disparity becomes apparent before puberty, and childhood obesity tends to track into adulthood. However, it is unclear whether ghrelin regulation differs with ethnicity or age. Additional aims were to determine whether ghrelin levels would differ between European American (EA) and African American (AA) adults and to compare ghrelin among AA females across different age groups. To address the first two aims, 61 overweight EA and AA men and women were assigned to either a higher-carbohydrate/lower-fat diet (55% CHO, 18% PRO, 27% FAT) or a lower-carbohydrate/higher-fat diet (43% CHO, 18% PRO, 39% FAT) for 8 weeks. After overnight fasts at week 0 and week 8, participants ingested a standard liquid mixed macronutrient meal. Blood was sampled before the meal and serially for 4 hours post-challenge to measure serum total ghrelin. For the third aim, 46 overweight AA females (28 girls, ages 8-15 years, and 18 premenopausal women) completed a liquid meal test. Fasting and post-challenge ghrelin concentrations were compared between age groups and across pubertal stages. Diet habituation did not affect fasting ghrelin or ghrelin response to the standard meal. However, EA exhibited higher fasting and postprandial ghrelin at weeks 0 and 8. AA demonstrated lower ghrelin suppression at week 0. Peri-pubertal AA girls displayed higher fasting and postprandial ghrelin compared to premenopausal AA women. Additional research is needed to identify factors other than habitual macronutrient intake that underlie differences in ghrelin regulation between ethnic and age groups as well as to examine whether blunted ghrelin suppression in AA or higher circulating ghrelin among AA girls before puberty influences obesity risk.

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