Prebiotics Enhance Magnesium Absorption and Inulin-based Fibers Exert Chronic Effects on Calcium Utilization in a Postmenopausal Rodent Model

Age-related changes in calcium metabolism play a role in the development of osteoporosis. A 4-wk feeding study was conducted in 5-mo-old ovariectomized (OVX) Sprague-Dawley rats to assess the effect of various dietary fibers on mineral metabolism and bone health parameters. There were 6 treatment groups: sham-Control, OVX-Control, OVX rats receiving daily estradiol (E2) injections, and OVX rats receiving an AIN-93M diet supplement with either an inulin-based fiber (Synergy1 (R) or Fruitafit HD (R)) or a novel fiber (polydextrose) at 5% wt. of diet. Calcium and magnesium metabolic balances were performed after early (3 d) and late exposure (4 wk) to dietary treatments. Rats receiving polydextrose had significantly higher net calcium absorption efficiency and retention than all control groups and a trend (P= 0.10) for higher calcium absorption when compared to inulin-based fibers after early exposure but the advantage did not persist over long-term exposure. The inulin-based fibers had positive chronic effects on calcium metabolism that were related to changes in the gut, that is, production of short chain fatty acids and higher cecal wall weights. All fibers improved magnesium absorption and retention in early and late metabolic balances; effects on magnesium metabolism were more pronounced than for calcium.