Strength Training and Nutrition Development for African American Youth (STAND)

A.1 Aims

The overall goal of this project is to examine role of strength training as a therapeutic intervention to improve the cancer and obesity-related metabolic risk profile in African-American adolescents. The project is prompted by the urgent public health need to prevent and treat cancer and obesity-related problems, including diabetes and cardiovascular disease, in African-American adolescents, a population that is understudied and medically under-served in the Los Angeles area. A recent report from the Institute of Medicine underscored this major public health concern in the childhood obesity field:

"Children's health has made tremendous strides over the past century. In general, life expectancy has increased by more than thirty years since 1900 and much of this improvement is due to the reduction of infant and early childhood mortality. Given this trajectory toward a healthier childhood, the investigators begin the 21st century with a shocking development - an epidemic of obesity in children and youth. The increased number of obese children throughout the US during the past 25 years has led policymakers to rank it as one of the most critical public health threats of the 21st century. (92)" Obesity and metabolic syndrome problems disproportionately affect African-American adolescents (51). This project will explore why African-Americans have greater cancer risk than Hispanics (91), despite a reduced prevalence of the metabolic syndrome (7, 62).

Preliminary work from this laboratory has shown that both African-American and Hispanic children are more insulin resistant than Caucasian children, and this difference is apparently not explained by differences in body fatness. Moreover, the metabolic compensation to a similar degree of insulin resistance markedly differs between African-American and Hispanic children (62). African-Americans display greater hyperinsulinemia in response to a glucose challenge, whereas Hispanics have a more subdued increase in insulin levels due to an increase in second phase insulin secretion. The investigators will have the opportunity to build upon this preliminary work to examine the effects of resistance training on three factors predictive of cancer and metabolic disease risk: 1) body fat distribution; 2) insulin resistance and 3) measures of oxidative stress in African America adolescents. The investigators previously studying Hispanic adolescents in a parallel protocol.

The overall hypotheses of this project are that: (1) hyperinsulinemia in overweight African-American youth is associated with increased long-term cancer risk; and (2) insulin resistance, obesity and oxidative stress in overweight African-American youth will be improved with chronic resistance training and a modified carbohydrate dietary approach. The investigators will specifically examine the following metabolic outcomes, because they have been hypothesized to contribute to the obesity-related increase in cancer and metabolic disease risk:

• Insulin concentrations and insulin sensitivity;
• Total body fat, abdominal visceral fat, muscle fat and liver fat;
• Circulating adipocytokines;
• Intima-media thickness of the carotid artery
• Markers of oxidative stress, including: F2-isoprostanes, malondialdehyde (MDA), myeloperoxidase (MPO), oxygen radical absorbance capacity and ROS detection by flow cytometry.

A.2 Aims

The specific aims and hypotheses of project 1 are as follows:

Study 1: Cross-Sectional Measures Specific Aim 1 (Body Fat Compartments): To determine the association of visceral fat, muscle and liver fat and plasma adipocytokines to variation in insulin resistance in African-American youth.

• Hypothesis 1: Visceral fat, muscle and liver fat, and adipokines will independently contribute to greater insulin resistance.

  • Specific Aim 2 (Insulin Resistance): To examine metabolic compensation to insulin resistance in African-American youth.

• Hypothesis 2: Insulin resistant African-American youth will exhibit a higher acute insulin response to glucose.

  • Specific Aim 3 (Oxidative Stress): To examine the influence of body fat and insulin resistance on markers of oxidative stress and markers of metabolic disease risk.

• Hypothesis 3: Increased total body fat and insulin resistance will be associated with greater oxidative stress. The increased oxidative stress will be correlated with the higher acute insulin response.

Study 2 (Randomized Trial of Modification of Carbohydrate Intake and Strength Training) • Specific Aim 4 (Linkage of factors in Aims 1-3): To determine the effects of a randomized modification of carbohydrate intake, and/or strength training intervention in overweight African-American adolescents on potential factors linking obesity, insulin resistance, and oxidative stress.

- Hypothesis 4: Strength training will improve metabolic factors for cancer risk. That is, resistance training will reduce visceral fat; increase insulin sensitivity, reduce hyperinsulinemia, and reduce oxidative stress. The decreases in total body fat and visceral adipose tissue will be associated with improved insulin sensitivity and oxidative stress.