Dietary protein, metabolic acidosis, and calcium balance

Chronic metabolic acid load induced by changes in dietary electrolyte balance increased chloride retention but did not compromise bone in growing swine

The effects of chronic dietary acid loads on shifts in bone mineral reserves and physiological concentrations of cations and anions in extracellular fluids were assessed in growing swine. Four trials were conducted with a total of 38 (8.16 +/- 0.30 kg, mean +/- SEM) Large White x Landrace x Duroc pigs randomly assigned to one of three dietary treatments. Semipurified diets, fed for 13 to 17 d, provided an analyzed dietary electrolyte balance (dEB, meq/kg diet = Na+ + K+ - Cl-) of -35, 112, and 212 for the acidogenic, control, and alkalinogenic diets, respectively. Growth performance, arterial blood gas, serum chemistry, urine pH, mineral balance, bone mineral content gain, bone-breaking strength, bone ash, and percentage of bone ash were determined. Dietary treatments created a range of metabolic acid loads without affecting (P > 0.10) growth or feed intake. Urine pH was 5.71, 6.02, and 7.65 +/- 0.48 (mean +/- SEM) and arterial blood pH was 7.478, 7.485, and 7.526 +/- 0.006 for pigs fed acidogenic, control, and alkalinogenic treatments, respectively. A lower dEB resulted in an increased (P < 0.001) apparent Cl- retention (106.6, 55.4, and 41.2 +/- 6.3 meq/d), of which only 1.6% was accounted for by expansion of the extracellular fluid Cl- pool as calculated from serum Cl- (105.5, 103.4, 101.6 +/- 0.94 meq/L (mean +/- SEM) for pigs fed acidogenic, control, and alkalinogenic treatments, respectively. A lower dEB did not decrease (P > 0.10) bone mineral content gain, bone-breaking strength, bone ash, percentage of bone ash, or calcium and phosphate balance. In conclusion, bone mineral (phosphate) was not depleted to buffer the dietary acid load in growing pigs over a 3-wk period.

Calcium intake and prostate cancer risk in a long-term aging study: the Baltimore Longitudinal Study of Aging

OBJECTIVE

To investigate the association between prostate cancer and calcium and other nutrients thought to influence the synthesis of 1,25-dihydroxyvitamin D [1,25(OH)2D].

METHODS

We included in the analysis 454 male participants in the Baltimore Longitudinal Study of Aging who were 46 to 92 years old at the time of completion of a food frequency questionnaire. Among them, 69 men were diagnosed with prostate cancer during their lifetime. In 68% of the cases, the food frequency questionnaire was completed after the diagnosis of cancer. Multiple logistic regression analysis was used to calculate the odds ratio and 95% confidence interval of prostate cancer.

RESULTS

The median calcium intake was 788 mg/day. The adjusted odds ratio of prostate cancer for the highest tertile compared with the lowest tertile of calcium intake was 0.92 (95% confidence interval 0.48 to 1.77; P(trend) = 0.89). Likewise, no significant trends were found for phosphorus, vitamin D, fructose, or animal protein intake. Dairy products, including milk, were not associated with an increased risk of prostate cancer. The adjusted odds ratio of prostate cancer was 1.26 (95% confidence interval 0.57 to 2.79; P(trend) = 0.73) for men with high dairy intakes compared with those with low dairy intakes.

CONCLUSIONS

The results of this study suggest that calcium intake within moderate limits is not associated with a notably increased risk of prostate cancer.

The effect of diet on lower urinary tract diseases in cats

Because dietary ingredients and feeding patterns influence the volume, pH and solute concentration of urine, diet can contribute to the etiology, management or prevention of recurrence of some causes of lower urinary tract disease. Most research assessing the effect of diet has focused on the latter two aspects, primarily because of interest in struvite urolithiasis. Manipulation of urine pH through dietary means has proven an effective tool for the management and prevention of struvite urolithiasis; acidification of urine, however, may be a risk factor for calcium oxalate urolithiasis, which now appears to occur with approximately equal frequency in cats. Prediction of urine pH from dietary analysis would thus be a valuable tool, but considerable further research is required before this can be achieved with commercial canned foods. With the growing importance of urolith types other than struvite, alternatives to the measurement of urine pH are required to assess critically the likely beneficial (or detrimental) effects of manipulation of nutrient profile. Measurement of urinary saturation may permit the development and fine tuning of nutrient profiles aimed at controlling lower urinary tract diseases in cats that are associated with a range of different mineral types. The majority of cats with signs of lower urinary tract disease do not, however, have urolithiasis; indeed, no specific cause can be established in most of these cats. Recent observations suggest that recurrence rates of signs in cats classified as having idiopathic lower urinary tract disease may be more than halved if affected animals are maintained on high, rather than low moisture content diets. J. Nutr. 2753S-2757S, 1998