Dietary Acid-Base Balance in High-Performance Athletes

Physical exercise leads to metabolic changes that a ect the acid-base balance in skeletal muscles and other tissues. Nutrition is one of the factors that may in uence the acid-base balance in the body. Keeping alkaline circumstances in the body is important not only for health and athletic performance in training but also during competition in many sport events. This is especially signi cant for athletes who practice in sport at the highest level of competition. The aim of the study was to determine the dietary acid-base balance in competitive Lithuanian high-performance athletes, and to evaluate the e ect of actual diets of athletes on NEAP (net endogenous acid production), muscle mass and body mineral content during a four-year Olympic cycle. The research participants were 18.1 3.3-year-old Lithuanian high performance athletes (n=323). The actual diet was investigated using the 24 h recall dietary survey method. The measurements of body composition were performed using BIA (bioelectrical impedance analysis). The potential renal acid load of the diets of athletes (dietary PRAL) and NEAP were calculated. In 10.2% of athletes, NEAP exceeds 100 mEq day 1 and is on average 126.1 32.7 mEq day 1 . Higher NEAP in athletes is associated with lower muscle mass ( -1.2% of body weight,p<0.001) but has no e ect on the amount of minerals in the body ( 0.01% of body

of athletes (dietary PRAL) and NEAP were calculated. In 10.2% of athletes, NEAP exceeds 100 mEq day 1 and is on average 126.1 32.7 mEq day 1 . Higher NEAP in athletes is associated with lower muscle mass ( -1.2% of body weight,p<0.001) but has no e ect on the amount of minerals in the body ( 0.01% of body weight,p=0.073). Overall, 25–30% of Lithuanian high-performance athletes use high-protein diets (2.0–4.8 g kg 1 day 1 ) leading to a dietary acid-base imbalance as well as an excessive production of endogenous acids in the body. Athletes are recommended to consume higher amounts of potassium and magnesium. An increase in calcium intake up to 1500 mg per day is recommended. In exceptional cases, periodised nutrition for athletes may involve diets complemented with bicarbonate and/or beta-alanine supplements. Keywords: high-performance athletes; actual nutrition; eating habits; diet; body composition; acid-base balance 1. Introduction Acid-base balance homeostasis is essential for ensuring health and physical performance indicators. Organic acids are produced in the body during basal metabolism, while physical exercise can lead to additional acid production in the body [1]. When engaged in sports, even submaximal exercise induces metabolic changes that a ect the acid-base balance in the skeletal muscles and other tissues [2]. Exercise intensity can lower blood pH from 7.4 to 6.9. It is noteworthy that the lowest blood pH reading Int. J. Environ. Res. Public Health2020,17, 5332; doi:10.3390 /ijerph17155332 /journal/ijerph

Int. J. Environ. Res. Public Health2020,17, 5332 2 of 19 (6.80–6.90) due to endogenous acids production was found in runners after a simulated 400 m race [3,4]. The increased H + levels in myocytes during high-intensity exercise lead to acidosis and fatigue [1,5]. Muscle fatigue occurs due to H + accumulation because the mitochondrial function and enzymatic activity are impaired. As a consequence, the production of glycolytic energy is disrupted [6,7]. It has also been proven that the concentration of H + ions leads to the accumulation of interstitial K + , where proteins bind H + ions instead of K + ions. This causes the hyperpolarisation of cells, inhibits the rate of the nerve impulse propagation, triggers the changes in the membrane potential and, as a result, disrupts the muscle function [8]. HCO 3 in extracellular uids is the major H + bu er [9]. Therefore, the maintenance of a higher concentration of HCO 3 results in a faster removal of H + from muscle cells [5]. Thus, an increase in the capacity of the acid bu er system improves the anaerobic [10,11] and aerobic [12] tness of athletes. The maintenance of alkalinity in intracellular uids enables a faster removal of H + from muscle cells resulting in a delayed muscle fatigue which occurs due to increased acidosis [1]. Nutrition is one of the factors that can a ect the acid-base balance in the body. This was con rmed by research that showed a strong relationship between the chemical composition of dietary intake and the urine pH range [13]. In this context, the possible in uence of the intake of di erent foods on the potential renal acid load (PRAL) was assessed. The PRAL index that shows the potential renal acid load indicates the presence of milliequivalents (mEq) of H + ions per 100 g of food. Most fruits and vegetables have a negative PRAL index because the biologically active substances found in them act as H + bu ers in the body. Meanwhile, foods high in protein and phosphorus have a positive PRAL index, which means that their

renal acid load indicates the presence of milliequivalents (mEq) of H + ions per 100 g of food. Most fruits and vegetables have a negative PRAL index because the biologically active substances found in them act as H + bu ers in the body. Meanwhile, foods high in protein and phosphorus have a positive PRAL index, which means that their consumption stimulates H + production in the body. According to the research, the dietary habits of the population in the developed countries with the typical Western diet are dominated by protein foods of animal origin ( sh, meat, eggs), leading to high levels of metabolic acidosis in the body [14]. The similarity in problems such as high protein and fat intakes was found among athletes from many countries. Based on the research data reported in the scienti c literature, it has been stated that a diet high in protein and fat, but low in carbohydrates was adopted by professional athletes from countries such as Poland [15,16], Iran [17], Kuwait [18], England [19,20], Brazil [21], Greece [22], Australia [23–25], France [26,27] Finland [28], China [29,30], Ireland [31], Netherlands [32], Spain [33,34], the United States of America (USA) [35], South Africa [36], Canada [37]. It has also been found that if athletes consume large amounts of protein and their diets are low in carbohydrates, they can su er from metabolic acidosis which can adversely a ect their physical performance [13,38–40]. In addition, insu cient consumption of potassium and magnesium with vegetables and fruits increases the risk of acidosis which may result in the reduced physical working capacity of athletes [41]. It should be noted that the presence of persistent acidosis in the body may trigger the impairment of the muscle function leading to the inhibition of muscle protein synthesis. Part of the amino acids from the degraded muscle proteins can be used for glutamine synthesis in the liver and, in later stages, for acid neutralisation. As a consequence, the increased acid production can lead to a decrease in muscle mass [42–45]. In addition, regular acidic diet may trigger a reduction in bone

to the inhibition of muscle protein synthesis. Part of the amino acids from the degraded muscle proteins can be used for glutamine synthesis in the liver and, in later stages, for acid neutralisation. As a consequence, the increased acid production can lead to a decrease in muscle mass [42–45]. In addition, regular acidic diet may trigger a reduction in bone mineralisation, an increase in urinary calcium excretion and pose a risk of bone fractures [46]. There are no scienti cally grounded data on how the diets of high-performance athletes impact their body's acid-base balance, muscle mass and body mineral content. The aim of the study was to determine the dietary acid-base balance in competitive Lithuanian high-performance athletes, and to evaluate the e ect of the actual diets of athletes on NEAP (net endogenous acid production), muscle mass and body mineral content during a four-year Olympic cycle.

Int. J. Environ. Res. Public Health2020,17, 5332 3 of 19 2. Materials and Methods 2.1. Study Population High-performance sport or elite sport is sport at the highest level of competition. The target population for the survey was high-performance athletes (n=341) included in the lists, approved under the orders the National Olympic Committee of Lithuania. The main inclusion criteria for study participants was quali cation standards that have been previously met by athletes. Only those athletes that had already obtained an Olympic quali cation quota place or the athletes who had participated in the European Athletics Championships and/or the World Athletics Championships for the purposes of Olympic quali cation were investigated. Those athletes who had not participation in sports competitions on a professional level were excluded from the survey. The size of the sample group (n=338) was selected using the OpenEpi Sample Size Calculator with a margin of error of 5% and probability of 99.9%. Over the period from 2017 through 2018, during a preparatory phase of training (macrocycle), 96% of the candidates (n=323) to the Lithuanian Olympic team were included in study and investigated. The athletes ranged in age from 16 to 33 (the average mean age of the athletes was 18.1 3.3 years) and were tested during the research and the training status of the athletes corresponded to 7.9 3.8 years, while workouts were done 5.8 0.8 days a week, with an average workout time of 175.6 60.6 min a day. The dimensions of the training workload of athletes fully complied with the training plans approved by the Lithuanian Sports Centre and the National Olympic Committee of Lithuania. The training plans were speci ed in the Tokyo 2020 and PyeongChang 2018 programmes. The research sample included 72.4% (n=234) men and 27.6% (n=89) women. According to the dominant energy expenditure methods, the subjects were divided into anaerobic 40.2% (n=130) and aerobic 59.8% (n=193) tness athletes [47]. The group of anaerobic athletes comprised weightlifters (n=6), gymnasts (n=3), discus, javelin throwers, shot put athletes (n=6), jumpers (n=4), basketball players (n=52), boxers (n=14), Greco-Roman wrestlers (n=29), judo wrestlers (n=12), and taekwondo wrestlers (n=4).

and 27.6% (n=89) women. According to the dominant energy expenditure methods, the subjects were divided into anaerobic 40.2% (n=130) and aerobic 59.8% (n=193) tness athletes [47]. The group of anaerobic athletes comprised weightlifters (n=6), gymnasts (n=3), discus, javelin throwers, shot put athletes (n=6), jumpers (n=4), basketball players (n=52), boxers (n=14), Greco-Roman wrestlers (n=29), judo wrestlers (n=12), and taekwondo wrestlers (n=4). The group of athletes of aerobic tness involved representatives of academic rowing (n=36), road cyclists (n=50), swimmers (n=66), skiers (n=17), biathletes (n=20), long-distance runners (n=13), representatives of modern pentathlon (n=12) and representatives of gure skating (n=2). A more detailed analysis of the study recruitment process and study procedures is provided in Figure.

Int. J. Environ. Res. Public Health2020,17, 5332 4 of 19Int. J. Environ. Res. Public Health 2020, 17, x 4 of 18 Figure 1. Flowchart of the enrollment of athletes and study procedures. BW—body weight; LBM—lean body mass; MM—mu scle mass; BF—body fat; PRAL—potential renal acid load; NEAP—net endogenous acid production; GFR—glomerular filtration rate. 2.2. Anthropometric Measures Target population High-performance athletes (n = 341) Study population Stud y nonparticipants High-performance athletes (n = 338) Non-professional athletes Study participants High-performance athletes (n = 323) Study intervention Body composition analysis by bioelectrical impedance The 24–hour dietary recall Eating habits survey by food frequency questionnaire Outcome measures Height, BW, LBM, MM, BF, mineral content in bones and electrolytes Evaluation of nutrient (protein, carbohydrates, fat, phosphorus, potassium, magnesium and calcium) intake The eating habits of athletes Group allocation X ↑ NH 4+Glutamine Neutralized H + ↑ Urinary Ca + Retained H + ↑ Bone resorption ↓ Serum bicarbonate ↓ Intestinal pH Decreased bone density ↓ Intracellular pH Fracture Diet: 20–50 mEq H + /day Metabolism: 35–60 mEq H + /day Total: 55–110 mEq H + /day High Low DIET PRAL (> 0 mEq H + /day) and NEAP (> 100 mEq H + /day) PRAL (≤ 0 mEq H + /day) and NEAP (≤ 100 mEq H + /day) Protein and phosphate (meat, poultry, fish, egg yolks and dairy) Potassium, magnesium and calcium (fruit and vegetables) Low High DIET ↑ Muscle catabolism Maximal urinary acid excretion (as H 2PO 4 -) Low GFR: approx. 45 mEq H + /day Residual H + ions 35–90 mEq H + /day Acid generated from: Data analysis Study inclusion and exclusion criteria Da ta col l ection Data comparison Sampling consent Figure 1. Flowchart of the enrollment of athletes and study procedures. BW—body weight; LBM—lean body mass; MM—muscle mass; BF—body fat; PRAL—potential renal acid load; NEAP—net endogenous acid production; GFR—glomerular ltration rate.

Int. J. Environ. Res. Public Health2020,17, 5332 5 of 19 2.2. Anthropometric Measures The height measurements in athletes were taken at the Lithuanian Sports Medicine Centre using a stadiometer ( 0.01 m). The measurements of the body weight and the individual weight components (body weight (BW), lean body mass (LBM) (in kg and %), muscle mass (MM) (in kg and %), body fat (BF) (in kg and %) and mineral content in bones and electrolytes) (in kg and %) were performed at the Lithuanian Sports Centre using the bioelectrical impedance analysis (BIA) tetra-polar electrodes (13 lot 21 block with certi cation EN ISO (an international standard is adopted by the European Union) 13488; Jinryang Industrial Complex, Kyungsan City, South Korea) and resistivity was measured with 8–12 tangent electrodes at di erent frequencies of the signal: 5, 50, 250, 550 and 1000 kHz [47,48]. LBM, MM and mineral content were assessed according to the norms set for men and women. LBM norm for men is 75–85%, for women 70–80%; MM norm for men is 74–80%, for women 64–80%; mineral norm for men ranges between 5.8–6.0%, for women 5.5–6.0%. The muscle and fat mass index (MFMI) of each athlete was determined by dividing the weight of the muscle (in kg) by weight (in kg). The BF and the ratio of muscle and fat mass were evaluated according to the standards presented in Table (MFMI) [47]. Table 1. Body fat (BF) percentage and muscle and fat mass index (MFMI) scale for athletes (by gender). BF MFMI Value Males Females Value Male Athletes Female Athletes Too low <5% <15% Insu cient <2 <1.8 Lean 5–9% 15–19% Too small 2.1–3.39 1.9–2.89 Optimal 10–14% 20–24% Moderate 3.4–4.69 3–3.99 Acceptable 15–19% 25–29% Extensive 4.7–6.0 4–5 Excessive 20–24% 30–34% Maximum >6 >5 BF—body fat; MFMI—muscle and fat mass index. 2.3. Energy Requirements The basal metabolic rate (BMR), daily energy expenditure (DEE), training energy expenditure (TEE) were estimated in all the subjects. BMR was calculated using the Harris and Benedict formulas [49]. We collected 24-h records of physical activity on the same day when the participants recorded their dietary

30–34% Maximum >6 >5 BF—body fat; MFMI—muscle and fat mass index. 2.3. Energy Requirements The basal metabolic rate (BMR), daily energy expenditure (DEE), training energy expenditure (TEE) were estimated in all the subjects. BMR was calculated using the Harris and Benedict formulas [49]. We collected 24-h records of physical activity on the same day when the participants recorded their dietary energy intake (EI). The physical activity levels and lifestyle variables (regular and non-regular activities, sedentary activities and sleeping habits) conform to the standards speci ed by the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine [50]. These measures (the activity codes and metabolic equivalents (METs) (in kcal/kg/h) for physical activities) were supported by the studies of Ainsworth et al. [51] and the data were processed according to the speci c activity. 2.4. Dietary Intake and Eating Habits The 24-h actual nutrition survey method was employed to assess the actual nutrition in athletes [52–54] . The respondents were surveyed through the direct interview carried out by a specially trained interviewer at the Lithuanian Sports Centre. The actual nutrition survey method facilitated the compilation of the data on the amounts of food, meals, food supplements consumed by each athlete. To capture all foods and meals eaten, and their amounts, a special atlas of photos with di erent portions of foods and meals weighted in grams was used [55]. We evaluated the average daily food sets consumed by athletes on the basis of which the chemical composition and energy value of food rations were determined in line with the chemical composition tables [56]. The consumption of carbohydrates, proteins and fats was assessed taking into account the recommendations provided in the scienti c literature [57,58]. The amount of carbohydrates recommended for athletes is 5–8 g kg 1 day 1 , protein content is 1.4–2.0 g kg 1 day 1 . The percentage of energy provided by fat should be between 20% and

recommended for athletes is 5–8 g kg 1 day 1 , protein content is 1.4–2.0 g kg 1 day 1 . The percentage of energy provided by fat should be between 20% and

Int. J. Environ. Res. Public Health2020,17, 5332 6 of 19 35%. The daily intake of minerals and their compliance with the reference daily intake (RDI) was assessed according to the RDI of vitamins and minerals approved in Lithuania [59]. To study the eating habits, we designed and used a validated questionnaire originally constructed by M. Baranauskas [60]. The respondents participated in direct interviews. The questionnaire comprised questions about the socio-demographics (gender, age, place of residence, sport, sporting experience, etc.) and eating habits of athletes. 2.5. Potential Renal Acid Load (PRAL), Net Endogenous Acid Production (NEAP) and the Diets The following formula was used to estimate the NEAP [61]: NEAP was estimated according to the equation (mEq day 1 )=PRAL 1 (mEq day 1 )+OA 2 (mEq day 1 ) where PRAL shows the potential renal acid load of the estimated diet and OA (organic anions) shows the urinary organic anions under analysis, with the 2 components calculated as follows: PRAL 1 (mEq day 1 )=(0.49 protein (g day 1 ))+(0.037 phosphorus (mg day 1 )) (0.021 potassium (mg day 1 )) (0.026 magnesium (mg day 1 )) (0.013 calcium (mg day 1 )). OA 2 (mEq day 1 )=individual body surface area 3 41/1.73. The body surface area was calculated according to the formula proposed by Du Bois and Du Bois [62]: 3 Individual body surface area (m 2 )=0.007184 height (cm) 0.725 weight (kg) 0.425 . 2.6. Statistical Analysis All the normally distributed continuous variables are presented as means standard deviations (SD), whereas the qualitative variables are presented as relative frequencies (in %). The normality of variable distribution was tested by the Shapiro–WilkWtest. When normality was con rmed, thet-tests of the independent samples were used to assess the di erences observed between the groups. Pearson (r) correlation coe cient were used to determine the strength of the relationship between the variables under analysis. The correlation coe cient r can range in value from 1 to+1. A higher degree of the absolute value of the coe cient shows a stronger the relationship between the variables. The correlations above 0.4 are

Study on dietary acid-base balance in Lithuanian high-performance athletes.