Overweight and obesity are increasingly prevalent worldwide. Weight excess increases the risk of in developing the metabolic syndrome, which is composed by a set of cardiometabolic risk factors such as abdominal adiposity, dyslipidemia, high blood pressure and elevated fasting glucose levels. Obesity and the metabolic syndrome are known to be risk factors for the development of chronic kidney disease. It is not clear however, whether they can be considered independent risk factors for impaired renal function and renal damage. Whereas obesity may represent an independent risk factor for renal damage, it is not clear yet if the contemporaneous presence of obesity and metabolic alterations is associated with an additional increase in the risk. It may be important to understand the relationship between obesity, metabolic syndrome and renal health, as treatment strategies may be different for the two metabolic phenotypes of obesity, i.e., metabolically healthy obese (MHO) and metabolically unhealthy obese (MUO) patients. The primary objective of this multicentre observational prospective study is to assess the relationship between metabolic phenotype and reduced renal function (glomerular filtration rate \<90 ml/min/1.73m2 or microalbuminuria 30-300 mg/24h) in a population of 1000 patients with overweight or obesity. The secondary aim is to study the association between diet quality, consumption of ultra-processed foods and indicators of reduced renal function and renal damage.