All of the following are the reasons for impaired absorption of calcium except:
Inositol hexaphosphate in cereals
High intake of oxalate
High concentrations of fatty acids in the intestinal lumen
Decreased iron intake
Phytic acid (inositol hexaphosphate) in cereals binds calcium in the intestinal lumen, preventing its absorption. Other minerals, including zinc, are also chelated by phytate. This is mainly a problem among people who consume large amounts of  unleavened  whole-wheat  products;  yeast  contains  an enzyme, phytase, that dephosphorylates phytate, so rendering it inactive. High concentrations of fatty acids in the intestinal lumen, as a result of impaired fat absorption, can also reduce calcium absorption by forming insoluble calcium salts; a high intake of oxalate can sometimes cause deficiency since calcium oxalate is insoluble.
HARPERS ILLUSTRATED BIOCHEMISTRY30th, Page No: 541