A low visceral fat proportion, independent of total body fat mass, protects obese adolescent girls against fatty liver and glucose dysregulation: a longitudinal study

Abstract

Background: The relative proportion of visceral fat (VAT) to subcutaneous fat (SAT) has been described as a major determinant of insulin resistance (IR). Our study sought to evaluate the effect of body fat distribution on glucose metabolism and intrahepatic fat content over time in a multiethnic cohort of obese adolescents.

Subjects/methods: We examined markers of glucose metabolism by oral glucose tolerance test, and body fat distribution by abdominal MRI at baseline and after 19.2 ± 11.4 months in a cohort of 151 obese adolescents (88 girls, 63 boys; mean age 13.3 ± 3.4 years; mean BMI z-score 2.15 ± 0.70). Hepatic fat content was assessed by fast-gradient MRI in a subset of 93 subjects. We used the median value of VAT/(VAT + SAT) ratio within each gender at baseline to stratify our sample into high and low ratio groups (median value 0.0972 in girls and 0.118 in boys).

Results: Female subjects tended to remain in their VAT/(VAT + SAT) category over time (change over follow-up P = 0.14 among girls, and P = 0.04 among boys). Baseline VAT/(VAT + SAT) strongly predicted the hepatic fat content, fasting insulin, 2-h glucose, and whole-body insulin sensitivity index at follow-up among girls, but not in boys.

Conclusions: The VAT/(VAT + SAT) ratio is a major determinant of impaired glucose metabolism and hepatic fat accumulation over time, and its effects are more pronounced in girls than in boys.

Fig. 1

Changes in VAT/(VAT + SAT) categories over time. Subjects in the low VAT/(VAT + SAT) ratio group at baseline tended to remain in the low group at follow-up, whereas subjects in the high VAT/(VAT + SAT) group at baseline tended to retain their group membership among girls, but not among boys. Light green indicates low VAT/(VAT + SAT) ratio and dark green indicates high VAT/(VAT + SAT) ratio group in girls. Light blue indicates low VAT/(VAT + SAT) ratio and dark blue indicates high VAT/(VAT + SAT) ratio group in boys. Numbers in histograms describe the number of adolescents by category and group

Fig. 2

Differences in hepatic fat content (HFF%) (a, b) and whole-body insulin sensitivity index (WBISI) (c, d) between low and high VAT/(VAT + SAT) ratio groups at baseline and follow-up in girls and boys. The data are expressed using box plots (5th percentile, median, 95th percentile). Light green indicates low VAT/(VAT + SAT) ratio and dark green indicates high VAT/(VAT + SAT) ratio group in girls. Light blue indicates low VAT/(VAT + SAT) ratio and dark blue indicates high VAT/(VAT + SAT) ratio group in boys

Fig. 3

Association of the baseline VAT/(VAT + SAT) ratio with whole-body insulin sensitivity index (WBISI), hepatic fat fraction (HFF, %), triglycerides, and fasting insulin at follow-up in girls, and boys (a–d). White circles indicate girls and black circles indicate boys