The assumptions made for the power calculation to estimate the number of volunteers are that a difference of 2.5% in iron absorption in the presence and absence of alginate ( test meal #1 and test meal #4) will be nutritionally significant. A minimum of 12 volunteers would be required to complete the study to detect a difference of 2.5% at a significance level of 0.05 for 80% power. A minimum of 8 volunteers would be required to detect a significant difference in iron absorption of 3.3% between a test meal containing 20mg of iron as iron gluconate with calcium and a test meal containing 20mg of iron as iron gluconate with calcium and alginate beads (test meals #2 and #3). This assumes a power of 80%, a level of significance of 0.05 and standard deviation of differences (within pairs) of 2.8%