The overweight and obesity are chronic metabolic disorders resulting from an excessive food caloric intake in relation to energy demands and lack of physical activity, which causes a positive caloric balance. As a consequence of overnutrition the extra calories are accumulated as body fat to the extent that it may have serious adverse effects on someones health. The most common and practical way of assessment the nutritional status is calculating the body mass index (BMI), also called the Quetelet’s Index. It is measured by dividing a weight in kilograms by height in square meters. If BMI exceeds 30 kg/m², a person is considered obese. The standard World Health Organization (WHO) definition from 1997 distinguished four levels of obesity. The first one is called moderate, second – severe, third – pathological, which is a life threating condition requiring medical intervention and may be an indication for bariatric surgery and the last one fourth level named superobesity. The levels of obesity and indicating BMI values are shown in table 1.

The importance of pathology is also fat distribution around the body. A special type is visceral obesity, which was differentiated by WHO due to connection with certain illnesses. In this type of obesity intra-abdominal adipose tissue is stored between internal organs in the peritoneal space. Because of constant hormonal and metabolic activity it highly correlates with developing cardiovascular diseases, increased risk of diabetes and malignancy. It is usually called central obesity due to significant abdominal protrusion in opposite to weight accumulation around the hips. The prevalence is higher in males. It is recognized using waist-hip ratio (WHR) (tab. 2).

An optimal body weight is multifactorial equation. It depends on age, gender, genetic susceptibility, comorbidities, sedentary lifestyle and dietary habits. The last two factors have the crucial meaning in obesity epidemic that affects western civilization. Obesity is the leading preventable cause of death worldwide causing 300 000 deaths each year, which can be up to twelve times higher than in communication accidents and ten times than in age-related population. In 1997 WHO recognized obesity as the global epidemic. Nowadays it affects 20% of world population and is considered a disease of affluence. During the last 20 years it’s prevalence increased by 50%. Including, it relates to over 1.1 million people. According to WHO data in 2015 there will be about 700 million people with BMI over 30 kg/m². In Poland the occurrence of pathological obesity is also still increasing and reached 18%. It is more common in females (2.2%) than in males (0.6%). In the USA it affects 5% of adults. The women in the age between 20 and 30 who achieved BMI > 45 kg/m² have the reduction of life- span of 8 year and men of 13 years than in general population (1, 2).

The obesity is an independent risk factor of CKD development, which in overweight patients is 40% and in obese 85% higher than in healthy controls. The initial kidney injury is caused by hyperfiltration, with time leading to proteinuria and glomerulosclerosis. The obesity involves blood pressure rise in response to compensation the decrease of renal plasma flow, increases the tubular sodium reabsorption, activates renin-angiotensin-aldosteron (RAA) system and stimulates renal sympathetic nerves. The metabolic and hormonal activity of visceral adipose tissue is considered to have an important role in pathogenesis of renal function disorder. Leptin increases tubular sodium reabsorption and influencing on tumor growth factor-β (TGF-β) and collagen type IV synthesis stimulates endothelial hyperplasia in the glomeruli. The adipose tissue secretes also proinflammatory cytokines and interleukins both aggravating fibrosis and proliferation. The glomerular disorder secondary to obesity has been termed in the literature as obesity related glomerulopathy (ORG). Its histological features are similar to that seen in focal segmental glomerular sclerosis (FSGS) with marked glomerular enlargement but lower podocytes foot-process seizure. Obesity associated conditions such as diabetes, hypertension, chronic heart failure, dyslipidemia significantly increase the risk of CKD occurrence. The more components of metabolic syndrome are present, the higher risk of CKD development is obtained (3).

Among the patients on renal replacement therapy, especially on haemodialysis the most common nutritional disorder is a protein-caloric malnutrition. MIA syndrome (malnutrition-inflammation-atherosclerosis) – a specific form of malnutrition in haemodialysed patients is associated with significantly increased mortality due to cardiovascular complications. The present recommendations for hemodialysed patients suggest increase in caloric intake up to 30-35 kcal/kg/day and protein up to 1.4 g/kg/day. Even if the recommendations are implemented the anthropometric features deteriorate within long term treatment. On the other hand reverse epidemiology paradox is documented on haemodialysis, which shows that patients with BMI > 27.5 kg/m² live twice as long as patients with normal BMI values. The reason of this phenomenon is seen in the coexistence of malnutrition and chronic inflammatory state.