Resistant Starches (RS2 and RS3) have Variable Effects on Bone Mineral Status in Rats

Abstract

Nondigestible oligosaccharides may increase mineral absorption by changing the intestinal environment. The effect of feeding a diet containing 5% resistant starch, RS2 (uncooked native) or RS3, (cooked and retrograded) on cal- cium absorption and bone mineral status was studied in growing male rats for 4 weeks. Almost 100g more feed was con- sumed with resistant starch compared to control in four weeks. Mineral status improved as determined by femur concen- tration, but not through absorption. Mineral content of femurs increased 12, 10 and 9% for Ca, Mg and Zn respectively, while Fe decreased 23% after feeding RS3, but not RS2, compared with the control group. There was no increase in the percent retention for any of the tested minerals. 45 Ca absorption capacity was not affected by either resistant starch. We conclude that resistant starches improve mineral status possibly through increased food consumption, but not through in- creased absorption efficiency. potato and high amylose starch, were compared at the same level and fed to rats for 7 days (12), no differences were found in calcium and magnesium absorption. Cecal concen- trations of calcium, potassium, and phosphate, but not of magnesium, were significantly increased in rats fed either 25% or 50% amylose-rich starch, 10% lactulose or 10% pec- tin compared to the control (13). The cecal pool of all these minerals was increased in a dose-dependent manner with the 25% and 50% amylose. All of the studies cited above used high levels of resistant starch (15 to 50%) and some (9,10) used higher levels of dietary calcium (up to 0.75%). The calcium requirement for rats is 0.5%. It is likely that any effect of calcium-absorption enhancers would be dampened above this level. The present study was designed to investigate the effect of two resistant starches, high amylose resistant cornstarch containing 60% resistant starch (RS2) and a high amylomaize retrograded resistant cornstarch containing 55% resistant starch (RS3), at 5% by weight on calcium absorption, mineral balance and bone mineral concentration in rats fed a 0.5% calcium diet.