The role of vegetables in the maintenance of acid-base balance and bone structure : a thesis presented in partial fulfillment of the requirements for the degree of Masters of Science in Nutritional Science at Massey University, Turitea, Palmerston North, New Zealand

Abstract

Metabolic acidosis may over time lead to osteoporosis by causing a release of calcium and other mineral phases from bone. The regular consumption of fruits and vegetables is believed to be associated with higher bone mineral density. In the last ten years various population-based studies have found positive effects of fruit and vegetable intakes on bone health. The aim of the present study was to investigate the effects of broccoli, onion, and potato on bone density and strength in male rats. Forty male Spraguc-Dawlcy rats were randomized into four equal groups of ten each. The animals were fed either a base, broccoli, onion, or potato diet for a period of eight weeks. The apparent percentage calcium and phosphorus retained, the serum type 1 collagen C-tclopcptide concentration, bone density and bone strength, and the urinary parameters i.e. ammonia, creatinine, urea, specific gravity and osmolality were determined. The groups on onion and potato diets had significantly higher apparent percentage calcium retained (over the balance period) than the group on control diet (p=0.02l and 0.008 respectively). Apparent percentage calcium retained was also significantly higher in the group on potato diet compared to the group on broccoli diet (p"0.037). There were no significant differences between groups for percentage phosphorus retained on ANOVA. However, the discriminant analysis (multivariate method) showed that the group on the broccoli diet retained significantly more phosphate over the balance period compared to the other groups. The urinary ammonia excretion (over the balance period) was significantly lower in the group on broccoli diet than in the groups on base and potato diets (p=0.040 and 0.055 respectively). As for the urinary urea excretion over the balance period, the group on base diet had significantly higher urea excretion than the groups on onion and potato diets (p=0.002 and p=0.000 respectively). Urinary urea excretion (over the balance period) was also significantly higher in the group on broccoli diet compared to the groups on onion and potato diets (p=0.005 and 0.000 respectively). The differences between groups for the volume of urine produced over the balance period were also significant i.e. the group on broccoli diet produced significantly more urine than the groups on base, onion, and potato diets (p=0.011. p=0.008. and p=0.00l respectively). However, there were no significant differences between groups for urinary specific gravity, osmolality, and creatinine, and bone density, bone breaking strength, and serum type I collagen C-telopeptide concentrations on ANOVA. In conclusion Ig of broccoli per day significantly reduced urinary ammonia excretion and increased apparent percentage phosphorus retained whereas Ig of onion or potato per day significantly increased apparent percentage calcium retained in growing male rats. The decrease in urinary ammonia excretion was most likely due to the buffering of metabolic acids by the bases present in broccoli resulting in decreased ammonia production and secretion. Similarly the increased apparent percentage phosphorus retained (in the group on broccoli diet) may be due to the bases present in broccoli that may have buffered metabolic acids thereby reducing the need for phosphate buffering. This increased apparent percentage phosphorus retained may also be due to a high pH which is known to enhance renal phosphate uptake. The buffering of metabolic acids by the bases present in onion and potato may have reduced the need for calcium buffering resulting in higher apparent percentage calcium retained in the groups on onion and potato diets. Thus broccoli, onion, and potato intake may protect against the bone depleting effects of an acidogenic diet and may also have the potential to increase bone mineral density.