It should be also noted that the iron supplements contain reduced Fe(II) ions, and not the oxidized Fe(III) ions that have been identified as cancer causes by this study.

The Fe(II) ions are soluble in water and they may also be found in natural water, but the Fe(III) ions normally form insoluble precipitates that would not have any effect even if they would pass through the intestine.

The Fe(III) ions that have been identified as harmful are those that are bound to organic molecules, e.g. proteins like hemoglobin, so that they are prevented from forming insoluble minerals.

Worth noting, eating 200g of beef is easy. Eating 200g of kale (or lentils) is challenging.