Rev Bras Fisiol Exerc 2021;20(2): 127-129
doi: 10.33233/rbfex.v20i2.4756
EDITORIAL
Resistance exercise and
protein supplementation influence kidney function?
Exercício
resistido e suplementação proteica influenciam na função renal?
Igor
Alonso Andrade de Oliveira1,2,3, Pedro Henrique Silva Santos1,4
1Faculdade do Oeste Paulista (FACOP), Bauru, SP, Brazil
2União Metropolitana de Educação e Cultura (UNIME), Salvador, BA, Brazil
3Grupo Pulsar, Salvador, BA, Brazil
4Escola de educação física e esporte da Universidade de São Paulo (USP), São Paulo, SP, Brazil
Correspondence: Igor Alonso Andrade de Oliveira, Rrua Silveira Martins, 100
Cabula, 41150-100 Salvador BA, Brasil
Igor Alonso Andrade de Oliveira:
igoroliveira13.1@baihana.edu.br
Pedro Henrique Silva Santos: phsantos@usp.br
Kidney
failure (KF) is characterized by the loss of the kidneys' ability to filter
metabolic wastes, salts, and blood fluids. The main causes of this disease are
systemic arterial hypertension and uncontrolled diabetes mellitus [1,2]. However, other causes are described, such as
the use of nephrotoxic drugs, prolonged dehydration and infection [1]. KF can be classified as acute (fast and
reversible) and chronic (gradual, slow and without reversibility) [1,2]. KF represents a serious public health problem
in Brazil. It is estimated that 134,000 chronic kidney patients require
replacement therapy (hemodialysis) [3]. These numbers grow every year, in 2018 alone
42,546 new people were diagnosed who needed this therapy [3].
Blood
creatinine and urea levels are the main biomarkers used to determine the
diagnosis of KF [4]. Creatinine is the metabolic product resulting
from the degradation of muscle phosphocreatine, used for the production of
adenosine triphosphate (ATP). As it cannot be reused by the body, creatinine is
easily filtered by the kidneys and is not reabsorbed at any stage of urine formation.
Therefore, it becomes the main marker of renal function [5].
Through
creatinine, it is possible to determine the glomerular filtration rate (GFR),
which consists of the capacity for the clearance of metabolic residues (urea
and creatinine) and salts (sodium, potassium, chlorine) by nephrons [1]. To do this, it is necessary to compare serum
and urinary creatinine levels after 24 hours [4]. GFR can also be estimated using
Cockcroft-Gault (CG) formulas [6] and that of the Modification of Diet in Renal
Disease (MDRD) study [7]. This measure is used to stratify the stage of chronic
kidney disease, considering as normal a GFR ≥ 90 mL/min and those with hemodialysis needing
those with GFR < 15 mL/min [1,4].
Urea is a
metabolic residue synthesized by the liver, resulting from the breakdown of
proteins ingested through the diet [8]. In the face of liver failure, kidney failure
or excessive protein consumption, serum urea levels may be increased causing
symptoms such as nausea, vomiting, shortness of breath, drowsiness, and
headache. Urea has low molecular weight, facilitating the glomerular filtration
process, with 50% being reabsorbed in the proximal contorted tubule. At low
flows as in dehydration situations, about 70% of urea is reabsorbed by the
kidneys [5].
In addition
to renal function, serum urea levels can determine the individual's protein
status in a short period of time [9]. Therefore, it is necessary to draw attention
to the doses of food supplementation in protein compounds such as Whey Protein
(milk protein). These supplements are used to gain muscle mass and strength, in
addition to helping with nutrition and wound healing. However, when the
individual's renal function is not properly dosed or analyzed, it can cause
severe complications [10].
Muscle mass
and the type of physical activity performed also contribute to the serum levels
of creatinine and urea. A study carried out in rural workers who performed
activities in the field with approximately 8h daily demonstrated that the time
of execution of the physical activity influences the doses of creatinine and
plasma urea, being higher in the individuals who collected the samples at the
end of the day, after work [11]. Another study carried out in trained
individuals showed an increase in creatinine and urea levels after intense exercise,
this is because during its execution there was an increase in creatine
metabolism and a reduction in urinary excretion, also increasing serum urea
levels [12].
In this edition of the Revista Brasileira de Fisiologia
do Exercício, Vieira et al. [13], published a clinical trial with male Rattus
Norvegicus Wistar Albino, supplemented with whey protein and compared to the
control. The rats were allocated into 6 groups in which: two groups were
supplemented with 2 g kg-1 d-1 (with and without
exercise) two with 4 g kg-1 d-1 (with and without
exercise), one group was the control training and the another only control. The
rats were submitted to neuromuscular exercise for 12 weeks with a frequency of
3x a week. The load determination was done through the maximum loaded weight
test (PMC) and the prescription was 4 climbs on the ladder per training session
with increasing intensity of 50%, 75%, 90% and 100% of the PMC.
The rats
that performed exercises associated with protein supplementation had higher
excretion of creatinine in the urine when compared to the control groups. When
performing a serum analysis, no statistical difference was identified between
the groups [13]. During intense exercise, there is an
increase in systemic blood pressure, resulting in an increase in glomerular
pressure [12]. These physiological adaptations increase
blood filtration processes, thus eliminating a greater concentration of
metabolic waste from the blood.
It is
possible to observe that the groups that did physical exercise associated with
protein supplementation also presented higher levels of urea concentration.
With the increase in hydrostatic pressure in the renal capillary due to intense
physical effort, the flow of the tubular fluid becomes faster, thus reducing
the reabsorption of urea in the contorted proximal, distal tubule and
collecting duct. Thus, it is justified to increase the concentrations of this
residue in the urine [14].
Studies like
this are necessary to identify the protein supplementation thresholds, in
addition to guiding professionals who work directly with physical exercise
regarding the correct prescription. Too many doses of supplementation and
exercise are harmful to the body, requiring more time to eliminate metabolic
excesses and organic regeneration [5,14]. In addition, it is necessary to pool the
information that constitutes individuals. Larger doses of supplementation
require adaptation of the type and intensity of exercise and the opposite
relationship also holds. That said, the study by Vieira et al. [13] draws attention to this theme and encourages
the production of new studies with similar proposals.