Dual-energy X-ray absorptiometry-assessed adipose tissues in metabolically unhealthy normal weight Asians

Abstract

Normal body mass index (BMI) is associated with lower risk for cardiometabolic diseases. However, there is a subset of individuals with BMI in this range who present with this metabolic abnormality (called metabolically unhealthy normal weight, MUHNW). Here we aimed to assess the adipose characteristics of people with MUHNW using dual-energy X-ray absorptiometry (DXA). This study included 3259 people with normal BMI who underwent health examinations from January 1, 2007 through December 31, 2016. Body fat percentage (%BF), android-gynoid percent fat ratio (AG ratio), and visceral adipose tissue (VAT) were measured simultaneously using DXA CoreScan software. Those with MUHNW comprised 12.67% of the sample. Among those with MUHNW, 71.6% of the women and 56.5% of the men showed high VAT amounts, but less than 40% of either showed high %BFs. Furthermore, considering the combined effects of fat amount and distribution, a normal BMI accompanied by high AG ratio and/or high VAT mass but low %BF presents a much higher risk for metabolic syndrome than when %BF is high, most predominantly in women. In conclusion, using DXA-measured abdominal fat, particularly VAT accumulation, is clinically more important than using %BF when assessing metabolic syndrome in those with normal BMI.

Figure 1

Odds ratios for metabolically unhealthy normal weight people grouped into quartiles for various fat indicators, independently in (a) women and (b) men. Quartile points for %BF were 29.84, 33.10, and 36.10 in women and 19.18, 22.27, and 25.09 in men; for AG ratio, they were 0.86, 0.96, and 1.05 in women and 1.19, 1.32, and 1.47 in men; for SAT mass, they were 863 g, 1024 g, and 1195 g in women and 602 g, 782 g, and 949 g in men; and for VAT mass, they were 250 g, 391 g, and 553 g in women and 513 g, 752 g, and 1005 g in men. %BF, total body fat percentage; AG ratio, android to gynoid percent fat ratio; SAT, subcutaneous adipose tissue; VAT, visceral adipose tissue. Adjusted odds ratios (95% CI) were analyzed using logistic regression with age as a covariate.

Figure 2

Scatter plots of percent of total body fat versus AG ratio and/or VAT mass. (a) and (b) are scatter plots for %BF versus AG ratio and/or VAT mass in women, respectively. (c) and (d) are scatter plots for %BF versus AG ratio and/or VAT mass in men, respectively. The vertical lines indicate the sex-specific 4th quartile point for %BF (36.10 in women and 25.09 in men), and the horizontal lines indicate the sex-specific 4th quartile point for AG ratio (1.05 in women and 1.47 in men) or for VAT mass (553 g in women and 1005 g in men). %BF, total body fat percentage; AG ratio, android to gynoid percent fat ratio; VAT, visceral adipose tissue.

Figure 3

Risk of metabolically unhealthy normal weight according to %BF versus AG ratio and/or VAT quartiles in (a,b) women and (c,d) men. Quartile points for %BF were 29.84, 33.10, and 36.10 in women and 19.18, 22.27, and 25.09 in men, for AG ratio, they were 0.86, 0.96, and 1.05 in women and 1.19, 1.32, and 1.47 in men, and for VAT mass, they were 250 g, 391 g, and 553 g in women and 513 g, 752 g, and 1005 g in men. %BF, total body fat percentage; AG ratio, android to gynoid percent fat ratio; VAT, visceral adipose tissue. Adjusted odds ratios (95% CI) were analyzed using logistic regression with age as a covariate.