Iron Deficiency Is Extremely Common
Iron deficiency affects an estimated 10% of women and 5% of men in the US. Globally, it is the most common nutritional deficiency. Symptoms include fatigue, weakness, pale skin, shortness of breath, cold hands and feet, and difficulty concentrating. Many people are mildly deficient without knowing it.
Heme Iron vs. Non-Heme Iron
Dietary iron comes in two forms:
- Heme iron (animal sources) — absorbed at 15–35% efficiency. Found in meat, poultry, and seafood.
- Non-heme iron (plant sources) — absorbed at 2–20% efficiency. Found in beans, spinach, and fortified foods.
This absorption difference matters enormously. Spinach contains 6.4mg of iron per cooked cup, but your body absorbs only about 1mg. A 3oz serving of beef contains 2.6mg of iron, and your body absorbs nearly 1mg. The effective iron intake is similar despite the raw numbers being very different.
Best Iron Sources Ranked
| Food | Serving | Iron (mg) | Type | Absorption Rate |
|---|---|---|---|---|
| Beef liver | 3 oz | 5.2 | Heme | High |
| Oysters | 3 oz | 7.8 | Heme | High |
| Beef (sirloin) | 3 oz | 2.6 | Heme | High |
| Dark chicken meat | 3 oz | 1.1 | Heme | High |
| Lentils (cooked) | 1 cup | 6.6 | Non-heme | Low-Moderate |
| Spinach (cooked) | 1 cup | 6.4 | Non-heme | Low |
| Kidney beans (cooked) | 1 cup | 5.2 | Non-heme | Low-Moderate |
| Fortified cereal | 1 serving | 8–18 | Non-heme | Moderate |
| Tofu (firm) | 1/2 cup | 3.4 | Non-heme | Low-Moderate |
| Pumpkin seeds | 1 oz | 2.5 | Non-heme | Low |
How to Maximize Iron Absorption
- Pair with vitamin C — eating iron-rich foods with vitamin C (citrus, bell peppers, tomatoes) increases non-heme iron absorption by up to 6x
- Cook in cast iron — iron leaches from the pan into food, adding 1–5mg per serving (especially with acidic foods like tomato sauce)
- Avoid calcium with iron-rich meals — calcium inhibits iron absorption; take calcium supplements at different meals
- Limit tea and coffee with meals — tannins in tea and coffee reduce iron absorption by 50–60%
- Combine heme and non-heme sources — eating meat alongside plant-based iron sources enhances absorption of both
Who Needs the Most Iron
- Women of reproductive age — menstruation increases iron needs to 18mg/day vs. 8mg for men
- Pregnant women — need 27mg/day to support fetal development
- Vegetarians and vegans — recommended intake is 1.8x higher due to lower absorption from plant sources
- Endurance athletes — increased iron loss through sweat and foot-strike hemolysis
- Frequent blood donors — each donation removes approximately 250mg of iron