Abdominal superficial subcutaneous fat: a putative distinct protective fat subdepot in type 2 diabetes

Abstract

Objective: Unlike visceral adipose tissue (VAT), the association between subcutaneous adipose tissue (SAT) and obesity-related morbidity is controversial. In patients with type 2 diabetes, we assessed whether this variability can be explained by a putative favorable, distinct association between abdominal superficial SAT (SSAT) (absolute amount or its proportion) and cardiometabolic parameters.

Research design and methods: We performed abdominal magnetic resonance imaging (MRI) in 73 patients with diabetes (mean age 58 years, 83% were men) and cross-sectionally analyzed fat distribution at S1-L5, L5-L4, and L3-L2 levels. Patients completed food frequency questionnaires, and subgroups had 24-h ambulatory blood pressure monitoring and 24-h ambulatory electrocardiography.

Results: Women had higher %SSAT (37 vs. 23% in men; P < 0.001) despite a similar mean waist circumference. Fasting plasma glucose (P = 0.046) and HbA(1c) (P = 0.006) were both lower with increased tertile of absolute SSAT. In regression models adjusted for age, waist circumference, and classes of medical treatments used in this patient population, increased %SSAT was significantly associated with decreased HbA(1c) (β = -0.317; P = 0.013), decreased daytime ambulatory blood pressure (β = -0.426; P = 0.008), and increased HDL cholesterol (β = 0.257; P = 0.042). In contrast, increased percent of deep SAT (DSAT) was associated with increased HbA(1c) (β = 0.266; P = 0.040) and poorer heart rate variability parameters (P = 0.030). Although total fat and energy intake were not correlated with fat tissue distribution, increased intake of trans fat tended to be associated with total SAT (r = 0.228; P = 0.05) and DSAT (r = 0.20; P = 0.093), but not with SSAT.

Conclusions: Abdominal SAT is composed of two subdepots that associate differently with cardiometabolic parameters. Higher absolute and relative distribution of fat in abdominal SSAT may signify beneficial cardiometabolic effects in patients with type 2 diabetes.

Figure 1

MRI imaging of abdominal fat tissues compartments. The subcutaneous fascial plane was delineated using the computer interface semiautomatic method, where initially an intensity-based automatic segmentation was generated and presented followed by semimanual fine tuning. The area of each compartment was quantitated separately. Fat tissues of specific anatomical landmarks were quantified and divided into color-coded groups as follows: dark blue, superficial subcutaneous fat; light blue, deep subcutaneous fat; green, visceral adipose tissue; and red, nonclassified fat—fat surrounding the vertebrae and fat depots that were unrelated to each of the groups listed above. (A high-quality digital representation of this figure is available in the online issue.)

Figure 2

Association of metabolic parameters and cardiovascular parameters with absolute abdominal fat tissues in patients with type 2 diabetes, stratified by sex. A: Entire group. B: Men only. Multivariate model adjusted for age and waist circumference. SSAT (black bar). DSAT (white bar). Numbers represent β standardized coefficient: the amount and direction by which absolute abdominal fat tissues change (mm²) for each unit change in the metabolic parameters, while accounting for the other variables in the model. TG, triglycerides (mg/day). *P < 0.05. †P < 0.1.

Figure 3

Association of metabolic and cardiovascular parameters with abdominal fat tissues distribution in patients with type 2 diabetes, stratified by sex. A: Entire group. B: Men only. Multivariate model, adjusted for age and waist circumference. SSAT% (black bar). DSAT% (white bar). Numbers represent β standardized coefficient: the amount and direction by which proportional abdominal fat tissues change (%) for each unit change in the metabolic parameters, while accounting for the other variables in the model. TG, triglycerides (mg/day). *P < 0.05.