When Adolescents Must Diet: Watch Zinc and Protein

Zinc's major role in metabolism, endocrine regulation, immune response, and normal growth and development in humans has been well documented. Failure to absorb sufficient zinc may constrain skeletal growth, reduce bone mineralization, cause inattentiveness, and predispose adolescents to infection. In adults, low zinc levels are linked to type 2 diabetes (T2D), decreased insulin sensitivity, and impaired glucose utilization.

Based on this knowledge, researchers from Westmead, Australia, investigated zinc's impact in adolescents who were at high risk for T2D. The researchers estimated bioavailability (phytate:zinc molar ratio) and plasma zinc concentration, then looked for links between zinc status and cardiometabolic markers in obese adolescents.

The researchers randomized 87 participants with clinical insulin resistance to 2 types of low-energy diets: high carbohydrate or moderate carbohydrate with increased protein.

Both diet groups included similar levels of zinc intake. Participants in the high-carbohydrate group ate more food considered high in phytates, averaging 25% more than the low-carbohydrate group. Phytates are antioxidants found in whole grains, legumes, nuts, and seeds; potatoes and wheat bran are the primary dietary sources for Americans. Phytates can bind to dietary minerals, including iron, zinc, manganese, and, to a lesser extent, calcium, as well as slow absorption.

Plasma zinc concentration showed a positive correlation with high dietary zinc intake and high protein intake, and negative correlations in the high-carbohydrate diet groups.

Participants who consumed the low-energy, high-carbohydrate diet had poorer estimated zinc bioavailability than those who consumed moderate carbohydrates coupled with increased protein content.

The researchers recommend that obese youths who need to follow low-energy diets to reduce their risk of diabetes may need increased protein content to optimize zinc bioavailability.