Effect of dietary cereal brans on the metabolism of calcium, phosphorous and magnesium in a long term rat study

Abstract

The effect of cereal brans on the mineral metabolism of rats was studied in a seven month long experiment. Seven groups (10 each) of male and female Sprague-Dawley weanling rats were fed ad lib for 7 weeks, diets containing cellulose, oat bran, hard red spring wheat bran, soft white wheat bran, corn bran and rodent lab chow at 4% or 14% total dietary fibre. In the seventh week (Phase 1) a mineral balance study was conducted on five randomly selected rats from each group. During week 8 these animals were killed and liver, heart, muscle and femur collected from each animal. The remaining animals were continued on the same diets for 21 more weeks. A second amineral balance study was carried out during week 24 (Phase 2) and the animals were killed during week 29 after colonic function tests during weeks 25–28. The diet, urine, feces and tissues were analysed for calcium, phosphorus, magnesium, phytate (in diet and feces only) and trace elements. Results on macro-mineral elements indicated that the fractional absorption of calcium, phosphorus and magnesium by male and female rats was not significantly different (P≤0.01). Absorption was affected by the level of the total mineral in the diet and not by the kind of fibre source. Variation in the digestibility of phytate was probably caused by the phytase activity in the bran rather than its phytate content. Digestibility during week 24 was less than during week 7 in most cases. The diets did not appreciably affect mineral levels in soft tissues and bone except the females in all purified diet groups showed severe nephrocalcinosis in both phases. Kidneys of males fed some diets showed mild calcification in phase 2. The absence of nephrocalcinosis in females fed the rat chow was associated with low levels of urinary phosphorus and also to the fluoride and high magnesium content of the chow.