Certain nutrients can interfere with absorption of other nutrients, thus impacting each other’s bioavailability. For example, calcium can interfere with absorption of iron depending on quantities consumed. Similarly, large amounts of zinc decreases copper absorption. Unless a medical condition warrants it, you should avoid taking individual mineral supplements for this reason. However, certain nutrients are also known to enhance absorption of other nutrients. Vitamin C promotes better iron absorption for instance. Indeed, oxalates can bind with both calcium and iron, partially limiting the absorption of these minerals during a meal. Spinach itself has plenty of calcium, but only about 5% of it can be absorbed because of its oxalic acid. In this case, having milk with spinach will assure that enough calcium is available for absorption. Ultimately it is best to eat a variety of foods including fruits and vegetables at every meal and snack to expose your body to a plethora of nutrients for use.