Adipose tissue from lean individuals comprises small, insulin-sensitive adipocytes that secrete large amounts of insulin-sensitizing adipokines under the influence of alternatively (M2)-biased adipose tissue macrophages (ATMs). In contrast, adipose tissue from obese individuals displays an expanded and prominently classically (M1)-biased population of ATMs, which secrete a variety of potent inflammatory mediators, together with hypertrophic, insulin-resistant adipocytes.