BLOOD AND URINE ACID-BASE STATUS OF PREMENOPAUSAL OMNIVOROUS AND VEGETARIAN WOMEN

The effect of long-term differences in diet composition on whole-body acid-base status was examined in thirty-three young healthy females. T he volunteers were recruited from two separate groups matched approxim ately for age, height and weight; one group regularly ate meat (omnivo res; n 20) and one group did not (vegetarians; n 13). All subjects com pleted a 7d weighed intake of food, and from their dietary records, to tal energy, carbohydrate (CHO), fat and protein content were estimated using computer-based food composition tables. During this week they r eported to the laboratory on two occasions, following an overnight fas t and-separated by at least 48 h. Arterialized venous blood samples we re obtained on each visit and these were analysed for blood acid-base status. Haemoglobin and packed cell volume, serum total cholesterol an d HDL-cholesterol, serum albumin and total protein were also determine d. Two 24 h urine collections were completed; the volume was recorded and samples were analysed for pH, titratable acid and Mg and Ca concen tration. Total energy intake of the omnivores was greater (P = 0.0003) than that of the vegetarian group. Dietary intake of CHO (P = 0.024), fat (P = 0.0054) and protein (P = 0.0002) were higher in the omnivoro us group than in the vegetarians. There were no differences between th e two groups with respect to blood CO2 partial pressure, plasma HCO3(- ) and blood base excess, but blood pH was slightly higher in the omniv ores (P = 0.064). Measures of urine acid-base status suggested a lower pH in the omnivore group, but this difference was not statistically s ignificant; a greater titratable acid output was observed with the omn ivorous group compared with the vegetarians (48.9 (SE 20.3) v 35.3 (se 23.3) mEq/24 h; P = 0.018). Although the dietary intake of Ca was not different between the two groups, urinary Ca excretion of the omnivor es was significantly higher (3.87 (SD 1.34) v. 3.22 (SD 1.24) mmol/24 h) than that of the vegetarians (P = 0.014). It is suggested that the higher protein intake of the omnivores resulted in an increase in urin ary total acid excretion, which may explain the higher rate of Ca excr etion.