Body fat may not impact insulin resistance

Homeostatic insulin resistance increases between the ages of eight and 10, but has no relationship with body fat, a longitudinal study finds. Researchers assessed 500 girls and boys for insulin resistance, body fat, physical activity and cardio respiratory fitness at age eight and again at age 10. Girls had a higher homeostatic insulin resistance at age eight, and this gap had increased substantially by age 10, although there was a substantial increase in insulin resistance for both sexes. There was no longitudinal relationship between insulin resistance and body fat percentage in boys or girls, although the boys showed a significant relationship between insulin resistance and both physical activity and cardio respiratory fitness. Consistent with other studies, however, there was a strong cross-sectional relationship between insulin resistance and body fat percentage in both sexes, as well as cardio respiratory fitness. The discordance between the longitudinal and cross-sectional relationships that insulin resistance had with body fat percentage, physical activity and cardio respiratory fitness was the most significant finding of the study, the authors said. There was little evidence to suggest the increase in insulin resistance were related to changes in body fat, while increases in physical activity and cardio respiratory fitness slowed the increase in insulin resistance for boys but not girls. Imprecise measurement of body composition was unlikely to be a factor, but factors associated with physical development may be a reason for the lack of a longitudinal relationship between insulin resistance and other factors in girls, they said. “Our study, in demonstrating the conflicting outcomes of longitudinal and cross-sectional investigations of relationships, highlights the potential hazards in interpreting observational studies,” the authors concluded. Pediatric Diabetes 2009: 10: 500–507. http://www3.interscience.wiley.com/journal/122370457/abstract...