Some food combinations create nutritional synergy, like plums increasing iron absorption. On the other side of the spectrum are food pairings that block absorption of vitamins and minerals. Calcium, a vital mineral for bone health, can be negatively affected by seemingly innocent foods. Two types of chemicals, oxalates and phytates, bind to the calcium and block your bodies ability to absorb the mineral.
Oxalates are found in spinach and rhubarb and phytates are found in bran and beans. Cheese sprinkled on a spinach salad should not be factored into your daily total of calcium consumption. Same goes for milk you eat over your bran cereal.
Since eating calcium is better absorbed by your body than a calcium supplement, make sure you're not undermining your efforts by combining the mineral with an unwanted chemical.