Obesity and renal disease: not all fat is created equal and not all obesity is harmful to the kidneys.

The prevalence of obesity is increasing worldwide and contributes to many health problems, including kidney disease. Unexpectedly, 10-30% of obese individuals are apparently not at increased risk of metabolic diseases, e.g. type 2 diabetes, cardiovascular disease and risk of renal disease. Their phenotype is labeled 'metabolically healthy obesity'. In the search for mechanisms explaining this unexpected condition, a favourable type of body fat distribution with low insulin resistance and with low subclinical inflammation has been identified. Furthermore, signalling pathways have been found that distinguish between metabolically benign and malignant obesity. In addition, the important roles of fatty acids, adipokines and hepatokines were identified. These factors regulate insulin resistance and subclinical inflammation. Onset and evolution of chronic kidney disease (CKD) are affected by obesity. CKD also increases the risk of insulin resistance and subclinical inflammation, two pathways that play an important role in the pathogenesis of renal malfunction. This brief review summarizes novel insights, specifically how distinct body fat compartments (including perivascular and even renal sinus fat) may have an impact on progression of CKD.