*2.3. Progression to CKD and ESRD*

Obesity has been associated with a higher incidence of CKD defined by the presence of albuminuria and/or GFR < 60 mL/min/1.73 m<sup>2</sup> as compared to the non-obese population [12,66–68]. The impact of obesity on conditions that favor the progressive decline of renal function has been emphasized. Low birth weight children, low renal endowment, subjects with reduced renal mass due to different origins, or with primary or secondary renal damage, displayed an increased risk of progression toward CKD and ESKD in the presence of obesity [69]. The role of metabolic abnormalities obesity-associated in the increment of risk has received attention. While some studies support that the metabolically healthy obese (MHO) do not have an increased risk of progression toward CKD and ESKD [70,71], or even a reduction in risk [72]. However, other studies are more in favour of MHO being the first stage of obesity [73] and that it is a question of time as to the development of metabolic abnormalities and consequently an increased risk of the development of renal dysfunction.

Individuals who are obese have a more than 3-fold higher risk of developing end-stage kidney disease (ESKD) than those with normal bodyweight [74,75]. In a large cohort from Austria, with a prevalence of obesity of 11.8%, 0.3% developed ESKD in a follow-up of 22 years and an increase of 5 points of BMI increased the risk by 56% [76]. In a cohort of the Kaiser Permanent register with 320,252 subjects followed over 21 years, the hazard risk for ESKD increased through the obesity grade 3.57, 6.10, and 7.07 for obesity 1 to III respectively, as compared with normal weight subjects [74]. However, when the rate of decline of renal function in CKD to develop ESKD was evaluated, controversial data had been reported. While some studies reported a faster decline [77] in the presence of obesity, other did not confirm [78].
