Low Glycemic Load Diets in Latino Children at Risk for Type 2 Diabetes

Overweight among minority children and adolescents is now the most prevalent pediatric public health problem in the United States. Our preliminary studies have found the prevalence of overweight among Hispanic children and adolescents in Washington DC is more than twice the U.S. national average. It is well established that overweight is associated with both medical and psychosocial complications, particularly for minority populations. Study of overweight Hispanic children has shown that they are at high risk for insulin resistance and impaired glucose tolerance (IGT), with IGT present in 28% of overweight Latino children with a family history of type 2 diabetes (T2DM). Despite the urgency to develop effective strategies to treat obesity and prevent T2DM in such children, few randomized controlled trials of weight management have been conducted in Hispanic children. Hence, there is an urgent need to develop effective, feasible and culturally competent obesity treatment programs targeted to Hispanic youth who are at great risk for obesity-associated co-morbidities, and who represent the fastest growing segment of the U.S. population.

A low-glycemic index (GI) or glycemic load (GL) diet is a much discussed, but quite controversial treatment of obesity. Some, but not all epidemiological studies show lower risk of diabetes among individuals consuming a low-GL diet. Short-term clinical studies examining the hormonal and biochemical responses to a low-GI diet have documented a reduction of reactive hyperglycemia and hyperinsulinemia, and decrease food intake. We propose that a low GL diet may be a particularly effective dietary regimen for overweight Latino children at risk for T2DM, who have a high consumption of processed and refined carbohydrate foods. The overall aim of this project is to determine the hormonal, metabolic, and body composition changes that occur during a two-year period of consumption of low-GL meals compared to low fat meals among Latino children at risk for T2DM. Our specific aims are:

• Specific Aim 1: To study the short- and long-term effects of a low-GL diet on insulin sensitivity in overweight Latino children at risk for T2DM.

Hypothesis 1: Insulin sensitivity will increase to a greater extent in children randomized to a low-GL diet than in children randomized to a reduced-fat meal prescription after 3, 12, and 24 months. The increase in insulin sensitivity found with a low-GL diet will not be fully explained by changes in BMI alone.

• Specific Aim 2: To determine the short- and long-term effects of a low-GL diet on BMI z-score and body fat changes in overweight Latino children at risk for T2DM.

Hypothesis 2: BMI z-score and body fat proportion will decrease to a greater extent in children randomized to a low-GL diet than in children randomized to a reduced-fat meal prescription after 3, 12, and 24 months observation periods.

• Specific Aim 3: To examine the effects of low-GL diet on markers of metabolic risk in overweight Latino children at risk for T2DM.

Hypothesis 3: Both traditional risk factors (e.g. systolic blood pressure, LDL-cholesterol, and triglycerides) and non-traditional risk factors (e.g. inflammatory [C-reactive protein, fibrinogen, and Plasminogen activating inhibitor -1], and adipocyte-derived factors [adiponectin, resistin, and free fatty acids]), related to insulin sensitivity will be lower in the low-GL meal group compared to the reduced-fat meal group at 3, 12, and 24 months.

• Specific Aim 4: To examine the subjective, hormonal, and metabolic responses of obese Hispanic youth to consumption of low-glycemic load and high glycemic load meals under controlled, standardized conditions.

Hypothesis 4: compared to the group fed high glycemic load meals, the low glycemic load group will have lower glucose and lower insulin responses, the low glycemic load group will report less hunger before their meals and greater satiety after their meals, and the low glycemic load group will consume less energy from a post-meal ad libitum snack platter.

Latino children ages 7-14y with BMI≥95th percentile and at-risk for T2DM will be randomly assigned either to a low-GL or a low-fat dietary plan for 2 years. Subjects will also participate in a culturally competent, family-based intervention program which includes behavior modification and enhanced physical activity. The frequence of intervention will consist of weekly visits for 12 weeks (Phase 1), monthly visits for 9 months (Phase 2), and 3-monthly visits for 12 months (Phase 3).

After completion of Phase 1, subjects will be admitted to the GCRC over a 24-hour period to participate in a meal study. Subjects will be provided with standardized meals consisting of either low-glycemic load (to the low-GL group) or high-glycemic load (to the high-GI group), and their subjective, hormonal, and metabolic responses will be assessed.

Inclusion criteria

• Hispanic children aged 7-14 years with BMI >= 95th percentile at risk for T2DM and who are otherwise healthy
• Ethnicity will be by self-identification with the Hispanic or Latino cultural group by the subject's parents and both sets of grandparents.
• At risk for T2DM defined as a positive family history of T2DM plus insulin resistance (fasting hyperinsulinemia ≥ 15 uIU/mL) or impaired glucose tolerance (fasting glucose >110 mg/dl, or 2-hour postglucose challenge >140 mg/dl).
• Only one child per family will be eligible to participate in the study

Exclusion criteria

• pre-existing T2DM
• Cushing syndrome
• untreated hypothyroidism
• pervasive developmental disorder
• severe asthma
• severe untreated depression
• use of medications that promote weight gain or loss
• obesity-associated genetic syndromes (e.g. Prader Willi syndrome)