Heme iron, which makes up about half of the iron in meat, poultry, and fish is absorbed two to three times more efficiently than iron (non-heme) from plants. So speaking strictly paleo wise, heme iron sources such as red meat, liver, scallops, clams and oysters are rich sources so they should be at the top of your list for go-to foods. Also. Dark green leafy vegetables (spinach, collards), dried fruit (prunes, raisins), eggs (the yolk) are good sources of iron. Iron absorption is increased markedly by eating foods containing vitamin C (or taking a supplement) along with foods containing iron.

Substances (such as polyphenols, phytates, or calcium) that are part of some foods or drinks such as tea, coffee, whole grains, legumes and milk or dairy products can decrease the amount of non-heme iron absorbed at a meal. Calcium can also decrease the amount heme-iron absorbed at a meal.

Also, simple things like taking antacids beyond the recommended dose or medicine used to treat ulcers and acid reflux which reduces the amount of acid in the stomach can inhibit your bodies ability to absorb iron.

Taking a supplement can sometimes constipate you, so be prepared for that.