Strength and Nutrition Outcomes for Latino Adolescents (SANO LA)

The overall historical goal of this grant has been to examine the determinants of insulin resistance in children, especially the role of total fat and visceral fat during pubertal development in "high risk" minority children. Our previous longitudinal work has provided the platform to propose a new intervention phase of this research. This new emphasis is justified based on the magnitude of the pediatric obesity problem, particularly in susceptible ethnic groups, and the need to design and test novel interventions to reduce not just obesity, but the profound insulin resistance that we have observed in overweight minority children. Insulin resistance is thought to be central (and perhaps causative) to several metabolic abnormalities associated with type 2 diabetes and cardiovascular disease. Thus, interventions aimed at improving insulin resistance in susceptible children could be an effective means in the primary prevention of type 2 diabetes and cardiovascular disease.

The overall objective of this proposal is therefore to conduct a randomized controlled study to examine the effects of 16-week exercise and diet interventions on insulin sensitivity, insulin secretion, beta-cell function, and body fat distribution. Overweight Hispanic boys and girls (n=80) will be recruited and randomized to one of the following interventions:

Ø Control (delayed intervention) Ø Modification of carbohydrate intake (reduced sugar & soda, increased fiber & whole grain intake) using an individualized healthy exchange system and motivational interviewing Ø Strength training + modification of carbohydrate intake Ø Circuit Training + modification of carbohydrate intake

This study will provide new information on the effects of these interventions on primary outcomes at the level of body composition (total lean and fat mass, visceral fat, intramyocellular fat and liver fat) and insulin related measures (insulin secretion & sensitivity and beta-cell function). The hypotheses are:

1. All interventions will have separate and independent effects on improving insulin resistance
2. Strength training will improve insulin resistance by re-distribution of body fat (lower visceral fat, intramyocellular lipid and liver fat)
3. Carbohydrate modification will improve insulin secretion and beta-cell function
4. Circuit training will have similar improvements in insulin resistance and have more improvements on adiposity compared to the strength training group.
5. The aforementioned effects on insulin dynamics will be independent of any effects of either intervention on weight loss or loss in whole body fat.

The overall rationale for these interventions is based on three main factors. First, preliminary data are presented in overweight Hispanic boys showing that 16-weeks of strength training significantly improves insulin sensitivity in the absence of a reduction in total body fat and in the absence of any dietary intervention. Second, preliminary data suggests that overweight Hispanic children consume high levels of simple sugar, and low levels of fiber and complex carbohydrates, and data from the literature suggests that modification of carbohydrate consumption (reduced sugar, increased fiber & whole grain) can improve glucose control independent of body composition. Third we provide new preliminary data showing that the only dietary variable associated with insulin dynamics in overweight Hispanic children was high sugar intake which was associated with poor beta-cell function.

We have chosen to focus on Hispanic children because they are an understudied, high-risk population, and display significant obesity-related metabolic abnormalities probably emanating from profound insulin resistance (see preliminary data). In support of the feasibility of our proposal, we have developed extensive expertise in recruiting and retaining research volunteers from the large Hispanic population of East Los Angeles, we have an experienced multi-disciplinary group of investigators, and the University of Southern California has the necessary clinical research infrastructure to tackle this project. If our hypotheses are borne out, it will provide evidence for the incorporation of strength training and more specific and individualized dietary recommendations in the prevention and management of obesity, type 2 diabetes, and cardiovascular risk in overweight Hispanic youth.