All of the following are the reasons for impaired absorption of calcium except:
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
Inositol hexaphosphate in cereals
High intake of oxalate
High concentrations of fatty acids in the intestinal lumen
Decreased iron intake