Excessive body weight is defined by the body mass index (BMI) ranging from 25 to 29.9 kg/m2, while obesity is defined as a body mass index equal to or greater than 30 kg/m2. Every second person in Europe today has excess body weight (Figure 1), and almost every third person is obese, which can be considered a true epidemic. Particularly dangerous is central obesity (accumulation of fat predominantly in the abdominal area), significantly increasing the risk of cardiovascular diseases. In addition to well-known risks associated with obesity, such as cardiovascular diseases, insulin resistance, and the development of diabetes, there is another risk that is not often discussed but is equally important: the risk of developing chronic kidney disease.
Indeed, the risk of chronic kidney disease in obese individuals is up to 40% higher than in people of normal body weight (1) and proportionally increases with the rise in the body mass index. There is now a specific definition for such kidney damage known as obesity-related glomerulopathy. The nephron, consisting of glomeruli and tubules, is the main functional unit of the kidney responsible for various tasks in the body (regulation of electrolytes and other substances, elimination of unwanted metabolic products, regulation of blood pressure, maintenance of blood acid-base balance, etc.). Due to the numerous functions the kidney performs through nephrons, kidney disease brings a range of issues to the body. When the kidney is not functioning properly, numerous medications are required in chronic therapy to try to compensate for the decreased kidney function.
Results of kidney tissue sample analysis in obese patients have shown various damages in nephrons due to excessive salt and fat intake, metabolic and hormonal activity of adipose tissue causing inflammation in the body, increased oxidative stress, and it's important to mention the disruption of hormonal regulation of blood pressure. Therefore, hypertension and obesity often go hand in hand.
In obese individuals, there is a volume overload on nephrons, initially resulting in excessive kidney function (known as glomerular hyperfiltration). All of this eventually leads to permanent scar damage to nephrons and reduced kidney function. Impaired kidney function is also associated with increased protein loss (especially albumin), further enhancing the already substantial cardiovascular risk in obese patients. Such patients are more prone to kidney stones and malignant kidney diseases (2). Another challenge in daily work with such patients is assessing kidney function. Current formulas for estimating kidney function are adapted to the population of normal body weight and surface area, and using these formulas in obese individuals leads to incorrect estimates of kidney function, resulting in incorrect drug dosages, misjudgment of cardiovascular risk and the risk of death, and numerous other issues in the diagnostic and therapeutic approach to this population (3).
Even a 1 kg loss in body weight can reduce the loss of these proteins by 4%. Obese individuals who undergo gastric volume reduction surgery (bariatric surgery) have normalized kidney function from excessive to normal values, along with a reduction in albumin loss (4).
What everyone can do for themselves is to pay attention to daily caloric intake through diet and salt intake (recommended up to 5g/day) and engage in regular physical activity. There are numerous online calculators that calculate the body's daily calorie needs (e.g., Total Daily Energy Expenditure Calculator), significantly facilitating the assessment of caloric intake needs for each individual separately. According to the World Health Organization recommendations, every adult should engage in moderate physical activity for at least 150 minutes per week. The emphasis here is on aerobic physical activity, which is associated with fat loss and has a favorable effect on blood pressure. This means setting aside at least 20 minutes a day for some aerobic activity (e.g., brisk walking, swimming, cycling...) leading to moderate fatigue and achieving a heart rate of up to 110/min.
Nephron - the basic unit for blood purification in the kidney.
Aerobic physical activity - energy for muscle movement is obtained in biochemical reactions where substances from food are broken down with the help of oxygen. Therefore, aerobic activity refers to the presence of oxygen. Such exercises are longer-lasting but of lower intensity.
(1) Sikorska D, Grzymislawska M, Roszak M, Gulbicka P, Korybalska K, Witowski J. Simple obesity and renal function. J Physiol Pharmacol. 2017;68(2):175-180. (2) Kovesdy CP, Furth S, Zoccali C. Obesity and kidney disease: Hidden consequences of the epidemic. Indian J Nephrol. 2017; 27(2): 85–92. (3) Gharbi MB, Elseviers M, Zamd M, Belghiti Alaoui A, Benahadi N, Trabelssi EH et al. Chronic kidney disease, hypertension, diabetes, and obesity in the adult population of Morocco: how to avoid "over"- and "under"-diagnosis of CKD. Kidney Int. 2016 ;89(6):1363-71. (4) Coupaye M, Flamant M, Sami O, Calabrese D, Msika S, Bogard C et al. Determinants of Evolution of Glomerular Filtration Rate After Bariatric Surgery: a 1-Year Observational Study. Obes Surg. 2017 ;27(1):126-133.
