**5. Diagnosis of abdominal subcutaneous ASC differentiation as a predictor of weight loss and metabolic outcome in bariatric patients**

Large evidence indicates that enlargement of adipocytes in obesity is associated with low-grade chronic inflammation which further leads to abnormal adipokine release and impaired glucose metabolism [61]. In obese patients with associated diabetes mellitus, VAT contains larger adipocytes and fewer preadipocytes as compared to SAT [62]. However, studies that examined the relationship between generalized and regional adiposity and insulin sensitivity in type 2 diabetic patients concluded that upper-body SAT (abdominal) plays a major role in obesity-related insulin resistance in comparison to visceral or retroperitoneal fat. These results suggest that upper-body SAT had a stronger correlation with insulin sensitivity than VAT among type 2 diabetic men [16].

Studying the response to overfeeding in upper- and lower-body SAT, Tchoukalova et al. [63] reported the hypertrophy of upper-body (abdominal) adipocyte and hyperplasia of lower-body (gluteofemoral) adipocyte to overfeeding in healthy men. In morbidly obese women with normal plasma glucose concentrations, mean adipocyte volume was larger in VAT than that in SAT, but these two depots did not differ in the proportion of small adipocytes. The ability of metabolically healthy obese to expand lower-body fat is a protective mechanism involving a hyperplastic response to energy overload. High rates of adipogenesis were associated with a smaller size of abdominal subcutaneous adipocytes, lower waist-to-hip ratio, and more favorable metabolic profile [63].

In bariatric patients, the adipocyte size and the preadipocyte content were assessed in SAT (abdominal) and VAT (greater omentum) by Muir et al. [25]. They observed modest correlations between adipocyte size and weight loss only in VAT. Independently of adipocyte size, the surgery-induced weight loss (12 month- %TWL) was direct correlated with pre-surgical preadipocyte frequency only in female subjects and this correlation was more robust in SAT than VAT.

Recently, CT-derived radiodensity measurement has been validated against ex-vivo adipose tissue samples for the assessment of tissue lipid. In morbidly obese patients, lower CT-derived adipose tissue radiodensity (corresponding to higher lipid content) in abdominal fat depots was associated with metabolic disorders [64, 65]. The post-surgery increase in abdominal SAT and VAT radiodensities reflecting decreased lipid content, increased tissue blood flow rate, and diminishing adipose inflammation was associated with a favorable metabolic state.

There is a growing body of evidence to suggest that studying the abdominal subcutaneous ASCs differentiation using biopsies or adipose CT radiodensity is important to understand the tissue responses to weight loss. The diagnosis of the adipogenic potential of abdominal subcutaneous ASC could predict the weight-loss and metabolic outcome in obese patients following bariatric surgery.
