Dietary acid load and acid-base balance in exercise and health from adolescence to late adulthood

Abstract

This thesis investigated whether dietary acid load has either short-term (4 to 7 days) or prolonged (12 weeks) effects on acid-base status at rest and during submaximal and maximal aerobic exercise; whether the effects of dietary acid load on acid-base status differ between adolescents, young adults and the elderly, and between men and women; and whether the changes in acid-base balance have a further effect on aerobic exercise performance. These questions were addressed in three different study settings in healthy and recreationally active men and women. In studies 1 and 2, which followed a crossover study design, participants were assigned in randomized order to follow a diet with a low or high acid load for 4 or 7 days. Study 3 was a 12-week longitudinal study in which participants were divided into two groups of lower and higher acid intake. Nine 18- to 30-year-old men participated in study 1. In study 2, 93 men and women were recruited from three age groups: 12 to 15 years, 25 to 35 years and 60 to 75 years. Forty-nine men and women aged 20 to 50 years participated in study 3. The main finding was that dietary acid load has acute and prolonged effects on blood and urine acid-base status and may also have effects on exercise performance. In young and elderly women, in particular, blood was more acidic at rest and during submaximal cycling after a 7-day high compared to low acid intake. In young women, maximal cardiorespiratory measures were lower and time to exhaustion shorter after high compared to low acid intake. During exercise, better renal function may be associated with higher bicarbonate ion availability in blood, which can diminish exercise-induced acidosis and delay fatigue. Lower kidney function in the elderly compared to younger participants, and in women compared to men may explain why the diet-induced changes in blood acid-base status were greater in the elderly participants and in women compared to younger participants and men. Moreover, even slightly acidogenic diets combined with regular training may be accompanied with increased acid load to the body and start to impair kidney function. These results emphasize the importance of an adequate intake of fruits and vegetables as a part of a healthy diet and a physically active lifestyle across the lifespan.