Background: Sodium bicarbonate (NaHCO ) is an alkalizing agent and its ingestion is used to improve anaerobic performance. However, the influence of alkalizing nutrients on anaerobic exercise performance remains unclear. Therefore, the present study investigated the influence of an alkalizing versus acidizing diet on 400-m sprint performance, blood lactate, blood gas parameters, and urinary pH in moderately trained adults. Methods: In a randomized crossover design, eleven recreationally active participants (8 men, 3 women) aged 26.0 ± 1.7 years performed one trial under each individual’s unmodified diet and subsequently two trials following either 4 days of an alkalizing (BASE) or acidizing (ACID) diet. Trials consisted of 400-m runs at intervals of 1 week on a tartan track in a randomized order. Results: We found a significantly lower 400-m performance time for the BASE trial (65.8 ± 7.2 s) compared with the ACID trial (67.3 ± 7.1 s; p = 0.026). In addition, responses were significantly higher following the BASE diet for blood lactate (BASE: 16.3 ± 2.7; ACID: 14.4 ± 2.1 mmol/L; p = 0.32) and urinary pH (BASE: 7.0 ± 0.7; ACID: 5.5 ± 0.7; p = 0.001). Conclusions: We conclude that a short-term alkalizing diet may improve 400-m performance time in moderately trained participants. Additionally, we found higher blood lactate concentrations under the alkalizing diet, suggesting an enhanced blood or muscle buffer capacity. Thus, an alkalizing diet may be an easy and natural way to enhance 400-m sprint performance for athletes without the necessity of taking artificial dietary supplements. Keywords: Acid-base balance, Blood buffer capacity, Potential renal acid load, Anaerobic exercise performance Background loads and improve acid-base balance in humans [5–7]. The modern Western diet is considered to be a rather In this context, new alkaline diets and supplements are acidic diet [1, 2], as it includes acid-forming nutritional being promoted and alkaline diets have gained popular- patterns like intake of high-protein, high-fat, and ity in the media over the last decade [2, 8]. high-cholesterol animal products and a lack of The physiologic effects of dietary components on base-forming intake of fruits and vegetables . The acid-base balance mainly involve the protein and mineral resulting metabolic acidosis is associated with diseases of (e.g., potassium salts) contents of the diet, intestinal absorp- civilization such as obesity, diabetes, systemic hyperten- tion rates of nutrients, and urinary acid excretion [9, 10]. sion, cardiovascular diseases and osteoporosis [1, 4]. The effects of ingested nutrients on acid-base balance Modifications to dietary composition reduce dietary acid can be quantified via the potential renal acid load (PRAL) [5, 11]. In general, meat, eggs, cheese, and cereal products promote systemic acidity (high-PRAL nu- * Correspondence: email@example.com trients) while potatoes, vegetables, and fruits have the high- Department of Sports Medicine and Sports Nutrition, Ruhr-University est alkalizing potential (low-PRAL nutrients) [7, 12, 13]. Bochum, Gesundheitscampus Nord 10, 44801 Bochum, Germany Institute of Outdoor Sports and Environmental Science, German Sports The PRAL model is a calculation model based on the University Cologne, Cologne, Germany © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Limmer et al. Journal of the International Society of Sports Nutrition (2018) 15:25 Page 2 of 9 − 3− 2− + + 2+ content of proteins, Cl ,PO4 ,SO4 ,Na ,K ,Ca ,and In summary, recent studies suggest that the ingestion 2+ Mg . PRAL can be calculated for each nutrient as fol- of a specific diet can modify blood buffer capacity, and lows: PRAL (mEq/100 g) = 0.49 × protein (g/100 g) + that changes in blood buffering capacity can influence 0.037 × phosphorus (mg/100 g) - 0.021 × potassium (mg/ high-intensity anaerobic exercise performance. There- 100 g) - 0.026 × magnesium (mg/100 g) - 0.013 × calcium fore, the purpose of the present study was to investigate (mg/100 g) . the influence of an alkalizing versus acidizing diet on Besides the mentioned negative health effects of an acid- 400-m sprint performance, maximum capillary blood izing diet, metabolic acidosis is further suggested to reduce lactate concentrations, blood gas parameters, and urin- exercise capacity during high-intensity exercise . In that ary pH in moderately trained young participants. We regard, it has been shown that ingestion of blood buffer hypothesized that an alkalizing diet will enhance extra- modifying agents like sodium bicarbonate (NaHCO )orso- cellular buffering capacity, and thus increase 400-m dium citrate can enhance high-intensity exercise perform- sprint performance. ance [14, 15]. Bicarbonate is an extracellular buffer and ingestion of NaHCO rises the bicarbonate concentration Methods ([HCO ]) in extracellular fluids. Thus, the elevated Participants − + [HCO ] stimulates the lactate/H cotransporter, which A total of 16 young and nonspecifically trained participants leads to a greater efflux of H ions from the intracellular volunteered to participate in the present study. Two partici- space into the extracellular fluid and allows buffering sys- pants withdrew from the study, due to busy time schedules. tems to remove H ions [15, 16]. The bicarbonate-induced Three participants had incomplete data. Results presented enhanced buffering capacity seems to improve are from the remaining 11 participants. The mean (± SD) high-intensity anaerobic exercise performance . age was 26.4 ± 1.8 y, with a mean height of 182.8 ± 6.9 cm The effects of a specific diet mainly containing alkaliz- and mean body mass of 82.0 ± 6.8 kg for male participants ing or acidizing nutrients on anaerobic performance, (n = 8) and 25.0 ± 1.0 y, 168.8 ± 1.4 cm, and 82.0 ± 6.8 kg however, has not been examined sufficiently, even for female participants (n = 3). All participants underwent a though nutrition influences acid base balance strongly medical screening before entering the study. All partici- [5, 7, 17]. Ball et al.  proposed that the ingestion of a pants wererecreationallyactiveand werefamiliar with diet low in carbohydrates and high in proteins and fat sprinting activities. Participants were randomly selected stu- (high-PRAL diet) reduces the capacity to perform dents who volunteered from university level physical educa- high-intensity exercise. The explanation of the authors, tion classes, and who practiced various physical activities however, mainly focuses on carbohydrate metabolism for ~ 12 h per week while pursuing their academic studies. and not on diet-induced metabolic acidosis. Further in- Participants had to be healthy and without any injuries to vestigations did not find an influence of an alkalizing the musculoskeletal system that could interfere with the diet on anaerobic performance [6, 19, 20]. However, Rios execution of running. Individuals ingesting any nutritional Enriquez et al.  suggested an improvement in anaer- supplements or following any specific diet in the 2 months obic exercise performance after an alkalizing diet for prior to the initiation of the study were excluded. All partic- tests with a duration of 60 s to 2 min. In addition, a ipants gave their written informed consent prior to partici- low-PRAL (alkalizing) diet improved the time to exhaus- pation and all procedures were approved by the ethical tion during anaerobic exercise . Further, an influence committee of the Ruhr-University Bochum in accordance on blood and urinary pH, as well as blood bicarbonate with the Declaration of Helsinki. values, has often been described when following either an acidizing or alkalizing diet [18, 21, 22]. Experimental design Caciano et al.  concluded with the practical implica- The study was designed as a randomized, single-blind, tion that the dietary manipulation of PRAL might bene- counterbalanced crossover trial (Fig. 1). Outcome asses- fit athletes and recommended a low-PRAL (alkalizing) sors were blinded for group affiliation. Participants were diet for athletes training and competing in events heavily informed about necessary modification of the diets to dependent on anaerobic metabolism, like 100–200 m achieve high or low PRAL values, but not about ex- swimming or 400–800 m running events. In addition, pected influences of the diets and associated hypotheses. significant performance improvements relative to pla- All participants performed three 400-m sprint exercise cebo trials were found for 400-m running events after tests at intervals of 1 week on an outdoor tartan track. oral NaHCO ingestion [23, 24]. Despite of these find- The three 400-m sprint exercise tests were performed in ings, in a recent review Applegate et al.  conclude that the morning at the same time of day. Before each 400-m alkalizing diets do not demonstrate the same effects as performance test, the participants completed a pre-test alkalizing agents like NaHCO on buffering capacity and warm-up, which included aerobic exercise and dynamic anaerobic performance. stretching. The first sprint trial served as habituation to Limmer et al. Journal of the International Society of Sports Nutrition (2018) 15:25 Page 3 of 9 BASE BASE n = 11 n = 6 400 m sprint randomization crossover n = 5 UNMOD ACID ACID 3 days TIMELINE washout 4 days 4 days dietary intervention dietary intervention DAY 1 DAY 8 DAY 15 Fig. 1 Experimental design the experimental protocol and was performed under characteristics of their stopwatch used in this study. We each individual’s unmodified diet (UNMOD). Therefore, used the same timer for each participant to attempt a data of this first sprint trial was not included in statis- higher interrater reliability of the hand-timing method, tical analyses. Four days before the two main trials, an and timers were positioned in consistent timing positions. acidizing (ACID) or alkalinizing (BASE) diet was followed in a randomized order. The first dietary inter- Urinary pH vention was followed by a 3-day washout phase with an Spontaneous urinary samples (at least 5 ml of urine) were unmodified diet before the second dietary intervention collected before each sprint trial. Urinary pH values (pH ) started in a crossover trial. Participants were instructed were measured using Neutralit® pH-indicator strips to abstain from alcohol and strenuous high-intensity ex- pH 5.0–10.0 (Merck, Darmstadt, Germany). This param- ercise 24 h before each trial and compliance with these eter served as a surrogate marker to assure that the dietary requests was verbally confirmed before each sprint trial. intervention had been conducted successfully . Dietary interventions Blood lactate For each of the dietary interventions, a medical dietician To assess blood lactate values, 20-μL capillary blood provided specific instructions for the modification of the samples were collected from the earlobe before and participants’ habitual diets to achieve high or low PRAL. every 2 min after the sprint trials, starting at minute 3 A modified German version of the original PRAL food and continuing to minute 13 (3,5,7,9,11,13). Blood lac- list published by the Institute for Prevention and Nutri- tate measurements were conducted directly after the tion, Ismaning, Germany, was distributed to the partici- sprint trial (Biosen S-Line, EKF-diagnostic GmbH, Mag- pants . Participants were instructed to make food deburg, Germany). The maximum post-exercise lactate choices and amounts ad libitum based on the respective concentration (La ) was used for statistical analyses. max PRAL values of foods. Participants were requested to document consumed foods and beverages on a food list during the dietary interventions. This enabled us to con- Blood gas analysis trol the overall PRAL values. Focus was on food com- Capillary blood samples (100 μL) were taken from the position with respect to its influence on acid-base hyperemized earlobe before and within the first minute balance, while energy intake was not documented. after each sprint trial. Measurements were immediately conducted for blood gas parameters (Eschweiler Combi- Performance time line, Eschweiler GmbH, Kiel, Germany). Parameters in- The overall 400-m performance time was measured using cluded oxygen and carbon dioxide partial pressure (PO / a stopwatch (Schütt PC-90, Schütt GmbH, Marburg, PCO ), blood pH value (pH ), oxygen saturation (sO ), 2 b 2 Germany). The timers were positioned right beside the active blood bicarbonate concentration ([HCO ]), and finish line and were instructed to initiate their stopwatches active base excess (BE). We further calculated the on the start signal and to stop when the sprinters first exercise-induced changes (Δ) of blood gas parameters foots pass the finish line. Each timer had several years of pre- versus post-sprint. Pre-exercise and Δ values were practice using a stopwatch and spent time learning the used for statistical analyses. Limmer et al. Journal of the International Society of Sports Nutrition (2018) 15:25 Page 4 of 9 Statistical analysis Data are presented as means ± standard deviations. The Shapiro-Wilk test was used to identify all departures from normal distribution. Paired sample t-tests were used to compare 400-m sprint performance times, La , max pre-exercise, post-exercise, and Δ blood gas parameters between the ACID and BASE conditions. In addition, paired sample t-tests were used to compare pre-exercise and post-exercise blood gas parameters. When variables were not normally distributed (pH ,pH pre-exercise, and u b PCO post-exercise), Wilcoxon tests were used to identify differences between the ACID and BASE conditions or pre- and post-exercise parameters. An a priori power cal- culation indicated that 11 participants were needed to de- tect significant differences in performance times, based on an estimated α level of 0.05 and a power of 95% (based on exercise performance enhancement results after an alkal- izing diet from an earlier study ).The alpha level was set UNMOD ACID BASE at p ≤ 0.05, and all analyses were conducted using SPSS 24 Fig. 3 Maximal blood lactate values after a 400 m running event for (IBM Corp., Armonk, NY, USA.). the acidizing (ACID) and alkalizing (BASE) diet trial. Data points represent individual values (○). Bar charts are means ± SD. See Results Methods for further details. *p = 0.032 compared with BASE The overall 400-m performance time was 2.3% faster in the BASE trial (65.8 ± 7.2 s) compared with the ACID trial (67.3 ± 7.1 s; p =0.026) (Fig. 2). La was significantly shown in Figs. 1, 2,and 3, but were not included in statis- max higher for the BASE trial (16.3 ± 2.7 mmol/L) compared tical analyses. with the ACID trial (14.4 ± 2.1 mmol/L; p =0.032) (Fig. 3). Post-exercise values were significantly lower compared Urine pH was significantly higher after the BASE diet with pre-exercise values for blood gas parameters pH, compared with the ACID diet (BASE: 7.0 ± 0.7, ACID: 5.5 [HCO ], BE, and sO ,but notfor PO and PCO during the 3 2 2 2 ±0.7; p =0.001) (Fig. 4). Data of the UNMOD trial are BASE trial (pH: p<0.000, [HCO ]: p < 0.000, BE: p < 0.000, 8.5 ** * 8 7.5 6.5 5.5 4.5 50 4 0 0 UNMOD ACID BASE UNMOD ACID BASE Fig. 2 400 m running time for the acidizing (ACID) and alkalizing Fig. 4 Urinary pH values after four days of the acidizing (ACID) and (BASE) diet trial. Data points represent individual values (○). Bar alkalizing (BASE) diet. Data points represent individual values (○). Bar charts are means ± SD. See Methods for further details. *p = 0.026 charts are means ± SD. See Methods for further details. *p = 0.007 compared with BASE compared with BASE performance time [s] pH La [mmol/L] max u Limmer et al. Journal of the International Society of Sports Nutrition (2018) 15:25 Page 5 of 9 sO : p = 0.004, PO : p = 0.712, PCO : p = 0.087) and during time, higher blood lactate, but unchanged blood pH values 2 2 2 the ACID trial (pH: p = 0.003, [HCO ]: p < 0.000, BE: compared with the acidizing diet. p < 0.000, sO : p = 0.006, PO p = 0.836, PCO2: p = 2 2: 0.182) (Table 1). There were no significant differences Urinary pH in any blood gas parameter between groups for In the present investigation, we found significantly higher pre-exercise, post-exercise, and Δ values (Table 1). urine pH values for the BASE trial (7.0 ± 0.7) compared There was, however, a non-significant tendency for a with the ACID trial (5.5 ± 0.7). Thus, we assume that the higher pre-exercise [HCO ] value in the BASE com- dietary intervention was conducted successfully because a pared with the ACID trial (p = 0.063). urine pH of ≥7.0 is expected for successful low-PRAL We also examined for a potential confounding effect by diets and ≤ 6.0 for high-PRAL diets [7, 25]. comparing the first and second sprint trials (independent of the dietary intervention) using a paired sample t-test. Sprint performance However, there was no difference between the two trials To the best of our knowledge, this is the first study to esti- (p = 0.606), suggesting that there was no training effect mate the influence of acid- and alkaline-forming nutrition that may have negatively influenced our test results. on anaerobic exercise performance with high applicability for a sport discipline. There are a number of studies esti- Discussion mating the effects of a dietary acid load on anaerobic exer- In the present study we investigated the influence of a cise performance using exercise tests exclusive to cycling 4-day alkalizing versus acidizing diet on 400-m sprint per- or treadmill running [2, 6, 7, 18, 21, 22]. However in a re- formance and associated physiological markers in moder- cent review, Applegate et al.  postulated a lack of stud- ately trained young participants. Our major finding is that ies examining different exercise intensities and measures the alkalizing diet results in an improved 400-m sprint of performance regarding an alkalizing diet. Additionally, Caciano et al.  recommended dietary manipulation of PRAL for sporting events where performance is limited as Table 1 Pre- and post- 400 m sprint values and sprint-induced result of acidosis, like 100–200-m swimming or 400– changes (Δ) of oxygen and carbon dioxide partial pressure (PO / PCO ), active blood bicarbonate concentration ([HCO ]), 800-m running events. Sprint performance for 400-m tri- 2 3 active base excess (BE), oxygen saturation (sO ), and blood pH als has already been suggested to improve after ingestion value (pH ) after 4 days of an acidizing (ACID) or alkalizing b of NaHCO [16, 23], but this has not been investigated for (BASE) dietary intervention an alkalizing diet. Therefore, based on the presumption ACID BASE p-value that an alkalizing, low-PRAL diet increases systemic al- PO pre - sprint 116.3 ± 26.4 118.7 ± 26.2 0.823 kalinity and blood buffer capacity, we hypothesized that [mmHg] an alkalizing diet also increases 400-m sprint perform- post - sprint 118.1 ± 19.1 115.5 ± 20.1 0.789 ance [7, 21]. Indeed, in the recent study, 400-m sprint Δ sprint 1.8 ± 28.3 −3.3 ± 28.6 0.653 performancetimewas significantlylower forthe BASE PCO pre - sprint 35.1 ± 3.5 36.5 ± 4.9 0.387 trial compared with the ACID trial, indicating that [mmHg] post - sprint 31.2 ± 7.5 33.3 ± 5.5 0.385 sprint performance was enhanced after consuming Δ sprint −3.9 ± 9.3 − 3.3 ± 5.7 0.732 mainly low-PRAL nutrients for 4 days prior to the [HCO ] pre - sprint 24.3 ± 2.0 25.9 ± 2.8 0.063 sprint test. However, the sprint performance enhance- [mmol/L] ment was only 2.3% in our study and less pronounced post - sprint 12.8 ± 3.3 13.0 ± 2.4 0.818 compared with the 21% increase of exercise perform- Δ sprint −11.4 ± 3.8 −12.9 ± 2.3 0.155 ance in the recent literature . We consider the differ- BE pre - sprint 1.30 ± 2.39 2.32 ± 2.20 0.184 ence in the performance tests as the main reason for [mmol/L] post - sprint −13.56 ± 3.39 −13.87 ± 3.27 0.780 this incongruence. Whereas we estimated performance Δ sprint −14.86 ± 3.82 −16.19 ± 2.88 0.310 as the run time for a fixed distance (time-trial test), sO pre - sprint 98.4 ± 0.9 98.5 ± 0.6 0.603 Caciano et al.  assessed anaerobic performance as [%] time-to-exhaustion while running on a treadmill with post - sprint 97.0 ± 1.2 96.8 ± 1.5 0.668 an individually defined and fixed speed. Open-ended Δ sprint −1.4 ± 1.3 −1.8 ± 1.6 0.449 protocols with time-to-exhaustion introduce larger pH pre - sprint 7.46 ± 0.05 7.47 ± 0.03 0.373 variability in performance output than distance-based post - sprint 7.24 ± 0.04 7.22 ± 0.07 0.294 performance tests, mainly because of motivational and Δ sprint −0.22 ± 0.06 −0.24 ± 0.07 0.347 mental aspects [23, 26]. Therefore, we assume that a Data is presented as mean ± standard deviation of the mean. No significant lower but more constant performance improvement is differences between groups were found using paired sampled t-tests or Wilcoxon to be expected for time-trial tests, such as a 400-m tests if variables were not normally distributed (pH pre-sprint and PCO b 2 post-sprint). n =11 sprint trial, compared with time-to-exhaustion tests Limmer et al. Journal of the International Society of Sports Nutrition (2018) 15:25 Page 6 of 9 after an alkalizing low-PRAL diet . Thus, 400-m (i.e., more energy demand per time unit) might indicate sprint performance time was enhanced after the a higher efflux of H ions from the muscle cell across low-PRAL diet, though the use of hand timing to meas- the interstitial space and into the venous circulation, cre- ure the 400-m time trial is one of the limitations of this ating a more severe metabolic acidosis. However, we study. The most precise and preferred method of tim- found no differences in blood pH between BASE and ing is by electronic methods because of the absolute er- ACID within the recent study. The lack of differences in rors associated with hand timing [27, 28]. For example, blood pH between both dietary interventions is probably variations among hand timers are likely to occur . a result of the higher blood buffer capacity because of Additionally, hand timing produces a faster sprint time high [HCO ] concentrations associated with an alkaliz- than electronic timing [28, 29], and a correction factor ing diet . of 0.2 s has traditionally been used for hand timing An augmentation of the [HCO ] concentration as . On the other hand, small mean errors (0.04– well as an increased blood pH can both be found after 0.05 s) and very high correlation values (ICC 0 0.99) sodium bicarbonate supplementation [15, 16, 24, 35]. have been observed between hand timing and elec- Unfortunately, the alkalizing or acidizing dietary inter- tronic timing, which indicates that hand timing pro- vention did not result in significant differences for any duces consistent sprint times for the same hand timer of the blood gas parameters within this study (Table 1). [28, 31]. Hand timing was the only method available to However, we found a slight tendency towards higher be used in evaluating sprint times in this investigation. [HCO ] values following a low-PRAL diet for 4 days Therefore, we decided to apply several measurement (Table 1). It has been suggested in recent literature that strategies supposed by Mayhew et al. inorder to alkalizing diets are unlikely to produce the same changes minimize problems with this method. We used the in buffer capacity compared with alkalizing ergogenic same timer for each participant to attempt a higher aids and that consumption of low-PRAL diets produces interrater reliability of the hand-timing method, and only a slight, but insufficient alkaline environment to en- timers were positioned in consistent timing positions hance buffer capacity [2, 13]. Our study, however, clearly perpendicular to the finish line. Each timer was profi- indicates that total buffer capacity must have been in- cient in the use of a stopwatch and spent time learning creased after a 4-day alkalizing diet because we did not the characteristics of the stopwatch used in this study. find changes in blood pH but increased blood lactate Furthermore, we asked the tester to initiate the timing concentrations and faster 400-m sprint times. Therefore, with the index finger and not with the thumb, as it was we assume that the non-significant tendencies towards previously reported that the most reliable and objective [HCO ] and BE values (Table 1) indicate a higher buffer handheld stopwatch times are achieved when the timer capacity after an alkalizing diet and might be more ap- uses the index finger to operate the stopwatch [28, 32]. parent when testing a larger sample size or longer dur- We think that these strategies reduced the errors asso- ation of the dietary intervention. ciated with hand timing and resulted in consistent sprint times within the present study. Practical applications First, a large inter-subject variation in PRAL from normal Blood lactate and blood gas analysis Western diets exists among athletes [6, 12]. Considering We found significantly lower values for the blood gas pa- this individual variability, sprint athletes and coaches rameters pH, [HCO ], and BE post-exercise compared should be encouraged to undergo a dietary assessment, with pre-exercise for both dietary interventions (BASE and including urine pH measurements, before an alkalizing ACID). This indicates a profound exercise-induced meta- diet is applied. Fasted morning urine pH can be monitored bolic acidosis after 400-m sprint trials for both conditions. for assessment and during the low-PRAL dietary interven- Further, we found higher maximum post-exercise lac- tion to confirm that the diet adequately alters dietary acid tate concentrations after 400-m sprint performance dur- load . Urinary pH values of ≥7.0 may be interpreted as ing the BASE trial compared with the ACID trial. a successful low-PRAL diet and values of ≤6.0 as Robergs et al.  state lactate production during in- high-PRAL diets [7, 25]. However, individual variability tense exercise more as a consequence rather than a must be considered when interpreting urine pH values. cause of cellular conditions that cause acidosis. However, Second, when consuming alkalizing diets, it is often these authors conclude that lactate is still a good indirect suggested to obtain the PRAL by increasing consumption marker for cellular metabolic conditions that induce of fruits and vegetables and minimizing consumption of metabolic acidosis because increased lactate production meats and grains . Based on this advice, a caloric deficit coincides with acidosis . Therefore, higher blood lac- during consuming alkalizing diets is reported . Conclu- tate values during the BASE trial within the recent study sively, especially for sprint athletes, the higher energy in combination with the improved 400-m sprint time demands and needs for dietary protein and carbohydrate Limmer et al. Journal of the International Society of Sports Nutrition (2018) 15:25 Page 7 of 9 sources, of which increase the PRAL, may make it difficult ingestion coupled with high intensity training may further to realize an alkalizing diet [6, 12, 13]. Regarding this prob- influence mechanisms associated with muscle force pro- lem, we highly advise the additional use of mineral waters duction or rapid force-generating capacity . The au- rich in bicarbonate to simplify the realization of an alkaliz- thors conclude that there is a lack of investigation into the ing diet [13, 36, 37]. Additionally, consumption of possible effects of chronic adaptions to training in an alka- carbohydrate-rich fruits and vegetables, such as fresh and lotic state. Regarding alkalizing dietary recommendations dried fruits, fruit juices, and potatoes, should be encouraged for sprint athletes, which are mainly chronic interventions, . A food diary might be used to control the amount of further research in this field is needed to clarify these train- foods eaten during a low-PRAL diet period. Food diaries ing effects in a chronic alkalotic state. can be analyzed for energy and macronutrient intake as well as for calculation of the overall PRAL per day. The lack Limitations of the study of food diaries as well as analyses of PRAL values, energy A limitation of our study was the use of hand timing, intake and macronutrient content is another limitation of which introduces a certain level of inaccuracy in measur- the present study. We asked our participants to report the ing 400-m sprint performance. Previous studies have foods eaten within each day of the dietary interventions, shown that electronic timing is the more precise and however, we did not collect amount of foods. Thus, we as- preferred method of timing [27, 28]. To reduce the po- sume that the dietary interventions had been conducted tential errors associated with hand timing, we applied successfully, because diaries mainly contained of vegetables several measurement strategies, including using the and fruits during the low-PRAL diet and of grain and dairy same timer for each participant, and consistent position- products during the high-PRAL diet. However, we were not ing of the timers perpendicular to the finish line . able to analyze energy intake or macro- and micronutrient However, future studies should consider electronic tim- content of the foods. Therewith we cannot report about an ing when investigating 400-m sprint performance in a influence of carbohydrate (CHO) content on sprint per- small sample size. Another limitation of the study is the formance, which has already been investigated [38, 39]. lack of quantitative information on food intake to allow Couto et al. showedthatahigh CHOdiet induced for detailed analyses of PRAL values, energy intake, and higher CHO oxidation rates and increased running speed macronutrient content. The participants were asked to in 400-m sprints. Although, we do not think that high provide daily qualitative food reports. However, the total CHO intake might have influenced the 400-m sprint per- amount and dietary composition were not controlled. formance for the low-PRAL trial positively in this study. The food reports conducted in our study mainly con- We presume low-PRAL dietary recommendations for that, tained vegetables and fruits during the low-PRAL diet, because recommendations limit the use of carbohydrate and grain and dairy products during the high-PRAL diet. sources (grains, e.g. bread or pasta) as they increase the The application of extensive nutritional analyses in fu- PRAL. Therewith, these dietary recommendations lead ture studies is required to support the validity of our more to caloric deficits during consuming alkalizing diets findings. Finally, there was a small sample size (n = 11) than to CHO loading . in our study, which resulted in wide confidence intervals In addition, some authors suggest a responder/non-re- and high p-values. Nevertheless, despite this limitation, a sponder phenomenon to the ergogenic potential of bicar- significant effect of dietary intervention was observed. bonate supplementation, with a tendency for highly trained athletes to show higher effects than untrained in- dividuals [15, 40]. Gastrointestinal (GI) discomfort is dosage-dependent for NaHCO ingestion and GI discom- Conclusion fort may negatively affect sprint performance [15, 41]. The present study was the first to examine the effects of Neither has been reported for a low-PRAL diet so far; a short-term alkalizing or acidizing diet on 400-m sprint however, we highly recommend a test phase for each ath- performance in moderately trained participants. Our lete during a non-competitive training period before chan- data suggest that it is possible to improve 400-m per- ging the usual diet during competitions to inhibit formance by consuming alkalizing (low-PRAL) natural discomfort from the dietary intervention. foods and beverages, without the ingestion of dietary Moreover, alkalizing low-PRAL diets lead to a chronic al- supplements like NaHCO or sodium citrate. Addition- kalotic state and, therefore, might be compared with ally, we found higher blood lactate but unchanged blood chronic use of NaHCO in some respects. There is evi- pH values for the alkalizing trial compared with the dence that despite the acute effects of bicarbonate ingestion acidizing trial. Thus, an alkalizing diet may be an easy on anaerobic performance in competitive situations, and natural way to enhance the tolerance towards chronic use of NaHCO in combination with specific train- exercise-induced alkalosis for athletes without the neces- ing may lead to aerobic adaptions. Chronic NaHCO sity of taking artificial dietary supplements. 3 Limmer et al. Journal of the International Society of Sports Nutrition (2018) 15:25 Page 8 of 9 Abbrevations 11. Deriemaeker P, Aerenhouts D, Hebbelinck M, Clarys P. Nutrient based [HCO ]: Active blood bicarbonate concentration; ACID: Acidizing diet; estimation of acid-base balance in vegetarians and non-vegetarians. Plant BASE: Alkalizing diet; BE: Active base excess; CHO: Carbohydrate; Foods Hum Nutr. 2010;65:77–82. cm: Centimeter; kg: Kilogram; La : Maximum post-exercise blood lactate 12. Aerenhouts D, Deriemaeker P, Hebbelinck M, Clarys P. Dietary acid-base balance max concentration; min: Minutes; NaHCO : Sodium bicarbonate; PCO : Carbon in adolescent sprint athletes: a follow-up study. Nutrients. 2011;3:200–11. 3 2 dioxide partial pressure; pH : Blood pH; pH : Urinary pH; PO : Oxygen partial 13. Arciero PJ, Miller VJ, Ward E. Performance enhancing diets and the PRISE b u 2 pressure; PRAL: Potential renal acid load; s: Seconds; SD: Standard deviations; protocol to optimize athletic performance. J Nutr Metab. 2015;2015:715859. sO : Oxygen saturation; UNMOD: Unmodified diet 2 14. Deldicque L, Francaux M. Functional food for exercise performance: fact or foe? Curr Opin Clin Nutr Metab Care. 2008;11:774–81. Acknowledgments 15. McNaughton LR, Gough L, Deb S, Bentley D, Sparks SA. Recent We are grateful to all participants for participating in this study. We thank developments in the use of sodium bicarbonate as an ergogenic aid. Curr our laboratory staff, Michaela Rau, for contributions and support. We also Sports Med Rep. 2016;15:233–44. thank Joel Anderson, PhD, for editing a draft of this manuscript. 16. Siegler JC, Marshall PWM, Bishop D, Shaw G, Green S. Mechanistic insights into the efficacy of sodium bicarbonate supplementation to improve athletic performance. Sports Med Open. 2016;2:41. Funding 17. Poupin N, Calvez J, Lassale C, Chesneau C, Tome D. Impact of the diet on net We acknowledge support by the DFG Open Access Publication Funds of the endogenous acid production and acid-base balance. Clin Nutr. 2012;31:313–21. Ruhr-University Bochum. 18. Ball D, Greenhaff PL, Maughan RJ. The acute reversal of a diet-induced metabolic acidosis does not restore endurance capacity during high- Availability of data and materials intensity exercise in man. Eur J Appl Physiol Occup Physiol. 1996;73:105–12. The datasets used and/or analyzed during the current study are available 19. Ball D, Maughan RJ. The effect of sodium citrate ingestion on the metabolic from the corresponding author on reasonable request. response to intense exercise following diet manipulation in man. Exp Physiol. 1997;82:1041–56. Authors’ contributions 20. Greenhaff PL, Gleeson M, Maughan RJ. Diet-induced metabolic acidosis and ML and PP conception and design of research; ML and PP performed the performance of high intensity exercise in man. Eur J Appl Physiol Occup experiments; ML and ADE analyzed data; ML, ADE, and PP interpreted results Physiol. 1988;57:583–90. of experiments; ML and ADE prepared figures; ML and ADE drafted 21. Rios Enriquez O, Guerra-Hernandez E, Feriche Fernandez-Castanys B. Effects manuscript; ML and PP edited and revised manuscript; ML, ADE, and PP of the metabolic alkalosis induced by the diet in the high intensity approved final version of manuscript. anaerobic performance. Nutr Hosp. 2010;25:768–73. 22. Hietavala E-M, Stout JR, Hulmi JJ, Suominen H, Pitkanen H, Puurtinen R, et al. Ethics approval and consent to participate Effect of diet composition on acid-base balance in adolescents, young adults This study was conducted in accordance with the Declaration of Helsinki, and the and elderly at rest and during exercise. Eur J Clin Nutr. 2015;69:399–404. protocol was approved by the ethical committee of the Ruhr-University Bochum. 23. Christensen PM, Shirai Y, Ritz C, Nordsborg NB. Caffeine and bicarbonate for All participants gave written informed consent prior to being enrolled in the study. speed. A meta-analysis of legal supplements potential for improving intense endurance exercise performance. Front Physiol. 2017;8:240. Competing interests 24. Siegler JC, Marshall PWM, Bray J, Towlson C. Sodium bicarbonate The authors declare that they have no competing interests. supplementation and ingestion timing: does it matter? J Strength Cond Res. 2012;26:1953–8. 25. Welch AA, Mulligan A, Bingham SA, Khaw K-T. 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Journal of the International Society of Sports Nutrition
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Published: May 31, 2018