Systemic acid load from the diet affects maximal-exercise RER

Department of Nutrition and Dietetics, Doisy College of Health Sciences, Saint Louis University, St. Louis, MO, USA.
Medicine and science in sports and exercise (Impact Factor: 3.98). 09/2011; 44(4):709-15. DOI: 10.1249/MSS.0b013e3182366f6c
Source: PubMed


A maximal-exercise RER (RER(max) ≥ 1.10 is commonly used as a criterion to determine whether a "true" maximal oxygen uptake (V˙O(2max)) has been attained during maximal-effort exercise testing. Because RER(max) is heavily influenced by CO2 production from acid buffering during maximal exercise, we postulated that dietary acid load, which affects acid-base regulation, might contribute to variability in RER(max).
The study's purpose was to determine whether a habitual dietary intake that promotes systemic alkalinity results in higher RER(max) during V˙O(2max) testing.
Sedentary men and women (47-63 yr, n = 57) with no evidence of cardiovascular disease underwent maximal graded treadmill exercise tests. V˙O(2max) and RER(max) were measured with indirect calorimetry. Habitual diet was assessed for its long-term effect on systemic acid-base status by performing nutrient analysis of food diaries and using this information to calculate the potential renal acid load (PRAL). Participants were grouped into tertiles on the basis of PRAL.
The lowest PRAL tertile (alkaline PRAL) had higher RERmax values (1.21 ± 0.01, P ≤ 0.05) than the middle PRAL tertile (1.17 ± 0.01) and highest PRAL tertile (1.15 ± 0.01). There were no significant differences (all P ≥ 0.30) among PRAL tertiles for RER at submaximal exercise intensities of 70%, 80%, or 90% V˙O2max. After controlling for age, sex, V˙O(2max), and HRmax, regression analysis demonstrated that 19% of the variability in RER(max) was attributed to PRAL (r = -0.43, P = 0.001). Unexpectedly, HRmax was lower (P ≤ 0.05) in the low PRAL tertile (164 ± 3 beats·min⁻¹) versus the highest PRAL tertile (173 ± 3 beats·min⁻¹).
These results suggest that individuals on a diet that promotes systemic alkalinity may more easily achieve the RER(max) criterion of ≥ 1.10, which might lead to false-positive conclusions about achieving maximal effort and V˙O(2max) during graded exercise testing.

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Available from: Gerald Stanley Zavorsky, Jan 05, 2014
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    ABSTRACT: Dietary acid load, quantified as the potential renal acid load (PRAL) of the diet, affects systemic pH and acid-base regulation. In a previous cross-sectional study, we reported that a low dietary PRAL (i.e. alkaline promoting diet) is associated with higher respiratory exchange ratio (RER) values during maximal exercise. The purpose of the present study was to confirm the previous findings with a short-term dietary intervention study. Additionally, we sought to determine if changes in PRAL affects submaximal exercise RER (as a reflection of substrate utilization) and anaerobic exercise performance. Subjects underwent a graded treadmill exercise test (GXT) to exhaustion and an anaerobic exercise performance test on two occasions, once after following a low-PRAL diet and on a separate occasion, after a high-PRAL diet. The diets were continued as long as needed to achieve an alkaline or acid fasted morning urine pH, respectively, with all being 4-9 days in duration. RER was measured during the GXT with indirect calorimetry. The anaerobic performance test was a running time-to-exhaustion test lasting 1-4 min. Maximal exercise RER was lower in the low-PRAL trial compared to the high-PRAL trial (1.10 ± 0.02 vs. 1.20 ± 0.05, p = 0.037). The low-PRAL diet also resulted in a 21% greater time to exhaustion during anaerobic exercise (2.56 ± 0.36 vs. 2.11 ± 0.31 sec, p = 0.044) and a strong tendency for lower RER values during submaximal exercise at 70% VO2max (0.88 ± 0.02 vs. 0.96 ± 0.04, p = 0.060). Contrary to our expectations, a short-term low-PRAL (alkaline promoting) diet resulted in lower RER values during maximal-intensity exercise. However, the low-PRAL diet also increased anaerobic exercise time to exhaustion and appears to have shifted submaximal exercise substrate utilization to favor lipid oxidation and spare carbohydrate, both of which would be considered favorable effects in the context of exercise performance. Key pointsShort-term (4-9 days) changes in the acid or alkaline promoting qualities of the diet, quantified as potential renal acid load (PRAL), alter systemic pH, as evidenced in the present study by changes in fasted morning urine pH. Low-PRAL (alkaline promoting) diets are characterized by high intakes of vegetables and fruits with limited consumption of meats, cheeses, and grains while high-PRAL diets are characterized by the opposite dietary pattern.An alkaline promoting (low-PRAL) diet increases anaerobic exercise performance, as evidenced by greater time-to-exhaustion during high-intensity treadmill running.Preliminary evidence suggests that an alkaline promoting (low-PRAL) diet increases lipid oxidation and may have a carbohydrate-sparing effect during submaximal endurance exercise, although further studies are needed.In contrast to what has been observed in response to habitual/long-term dietary patterns, a short-term low-PRAL diet does not increase maximal exercise respiratory exchange ratio and even appears to lower it. This suggests that short-term and long-term alterations in PRAL have different physiologic effects on this parameter.
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