Iron: From Earth's Crust to Our Plates

Introduction: The Geologist's Perspective on Iron

Iron, a critical element that shapes both our planet and our health, originates from the Earth's crust, forming through the intense processes of geological activity. Since I studied geology I marvel at how this metal, forged in the heart of stars and brought to our planet via ancient meteorites, plays such a vital role in human biology. Reflecting on my "I Am Life" design, which incorporates the chemical symbol for iron (Fe), has deepened my appreciation for how essential this element is to life itself. As a food connoisseur and health-conscious individual, I strive to consume foods that help me thrive.

In this article, I will provide you with a comprehensive list of iron-rich foods and explain how you can ensure your body is in a state to effectively absorb the iron it needs.

What is Iron?

Iron (Fe) is a metallic element, ubiquitous in the Earth’s crust. It’s a fundamental component of minerals such as hematite (Fe2O3) and magnetite (Fe3O4). These iron ores are extracted, refined, and utilized in various industries, but iron's journey doesn’t end in infrastructure or manufacturing—it extends to our very biology. In humans, iron is essential for oxygen transport, DNA synthesis, and energy production.

The Importance of Iron in the Human Body

Iron’s primary function in the body is to form hemoglobin, a protein in red blood cells responsible for carrying oxygen from the lungs to the rest of the body. It also plays a crucial role in myoglobin, a protein that provides oxygen to muscles. Iron deficiency can lead to anemia, characterized by fatigue, weakness, and impaired cognitive function. Thus, maintaining adequate iron levels is crucial for overall health and well-being.

Why Is Iron Important?

Iron’s main role in the body is oxygen transportation. Iron assists with the production of hemoglobin, a protein that carries oxygen from your lungs to the rest of your tissues and organs. Around 65% of the iron in your body is found in your blood, which gives your blood its bright red color.

In addition to oxygen transportation, iron is essential to growth and development, cellular function, and the production of certain hormones. Your body recycles and reuses iron from old blood cells, which covers up to 90% of your iron needs.

Your body also loses small amounts of iron daily. For example, most people lose about 1 milligram (mg) of iron through their poop every day.

How Much Iron Do You Need?

Iron needs depend on factors like age, as well as menstruation and pregnancy status. People who menstruate need more iron due to blood loss during their monthly period. Pregnancy and certain medical conditions—such as ulcerative colitis or cancer—also increase the body’s need for dietary iron.

Here are the daily recommended iron intakes for non-vegetarians:

• Men aged 19-50: 8 mg
• Women aged 19-50: 18 mg
• Men aged 51 and older: 8 mg
• Women aged 51 and older: 8 mg
• Pregnant women: 27 mg
• Breastfeeding women: 9 mg

Daily iron recommendations are about 1.8 times higher for vegetarians and vegans. This is because your body can absorb and use heme iron, the type of iron found in animal foods like meat, poultry, seafood, and eggs, better than non-heme iron, the iron in plant foods. Your body absorbs about 25% of dietary heme iron and about 17% of dietary non-heme iron.

Types of Dietary Iron

Dietary iron occurs in three major forms: ferrous iron (Fe2+), ferric iron (Fe3+), and heme iron (Fe2+ chelated into a complex organic compound to complete the heme structure, which occurs in hemoglobin, myoglobin, and certain enzymes). Ferrous iron and ferric iron may be present as part of, or attached to, many different inorganic or organic compounds, such as the oxide of iron or complexed with amino acids, citric acid, vitamin C, transferrin, ferritin, and iron-cytochrome reductase. Heme iron also enhances the absorption of non-heme iron, making it an important factor in ensuring adequate iron intake.

Iron-Rich Foods: Bridging Geology and Nutrition

Understanding iron’s geological origins enriches our appreciation of its nutritional sources. Let’s explore some foods that are abundant in iron, supporting our health by ensuring we receive this essential mineral.

Red Meat and Poultry

1. Organ Meats

   • Chicken Liver: 9.86 mg per 3 oz, or 54% DV
   • Beef Liver: 5.56 mg per 3 oz, or 31% DV
   • Beef Heart: 5.42 mg per 3 oz, or 30% DV

2. Red Meat

   • Venison Tenderloin: 3.61 mg per 3 oz, or 20% DV
   • Bison: 2.71 mg per 3 oz, or 15% DV
   • Beef Steak, Broiled: 1.56 mg per 3 oz, or 8% DV

3. Fish and Shellfish

   • Mussels (cooked): 5.71 mg per 3 oz, or 32% DV
   • Sardines: 2.69 mg per 3.75-oz can, or 15% DV
   • Salmon: 1.3 mg per 6 oz, or 7% DV

4. Poultry and Eggs

   • Duck: 3.78 mg per cup, or 21% DV
   • Dark Turkey Meat: 1.23 mg per 3 oz, or 7% DV
   • Hard-Boiled Eggs: 1.19 mg per two large eggs, or 7% DV

Seafood

Fish and shellfish provide many important nutrients, including iron, selenium, zinc, iodine, and vitamin B12. Seafood also provides omega-3 fats, which play important roles in immune function and inflammation regulation in the body.

Plant-Based Sources

1. Legumes

   • Tofu: 1.5 mg per 100 grams (19% of RDA)
   • Lima Beans: 4.1 mg per cup cooked (51% of RDA)
   • Black-Eyed Peas: 4.3 mg per cup cooked (53% of RDA)
   • Navy Beans: 4.3 mg per cup cooked (53% of RDA)
   • Tempeh: 4.5 mg per cup (56% of RDA)
   • Chickpeas: 4.7 mg per cup cooked (58% of RDA)
   • Red Kidney Beans: 5.2 mg per cup cooked (65% of RDA)
   • Lentils: 6.6 mg per cup cooked (82% of RDA)
   • White Beans: 6.6 mg per cup cooked (82% of RDA)
   • Soybeans: 9.9 mg per cup raw (123% of RDA)
   • Natto (fermented soybeans): 15.1 mg per cup cooked (188% of RDA)

2. Spinach and Other Leafy Greens

   • Spinach: 5.7 mg per cup cooked (71% of RDA)
   • Kale: Rich in iron and other nutrients.
   • Collard Greens: Similar nutritional profile to spinach.

3. Vegetables

   • Broccoli: 1 mg per cup chopped, cooked (12% of RDA)
   • Oyster Mushrooms: 1.1 mg per cup raw (13% of RDA)
   • Brussels Sprouts: 1.8 mg per cup cooked (22% of RDA)
   • Potatoes: 1.9 mg per large unpeeled potato (23% of RDA)
   • Tomato Paste and Canned Tomatoes: 2 mg per 1/4 cup (25% of DV) and 2.4 mg per cup (30% of RDA)
   • Sweet Potatoes: 2.2 mg per large peeled sweet potato (27% of RDA)
   • Sun-Dried Tomatoes: 2.5 mg per half cup (31% of RDA)
   • Beet Greens: 2.7 mg per cup cooked (33% of RDA)
   • White Mushrooms: 2.7 mg per cup cooked (33% of RDA)
   • Swiss Chard: 3.9 mg per cup cooked (48% of RDA)
   • Palm Hearts: 4.6 mg per cup canned (57% of RDA)

4. Mushrooms

   • Kikurage (dried): 35.2 mg
   • Arage-Kikurage (dried): 10.4 mg
   • Shiro-Kikurage (dried): 4.4 mg
   • Matsutake (canned in water): 3.3 mg
   • Maitake (dried): 2.6 mg
   • Shiitake, Hoshi-Shiitake (dried): 1.7 mg
   • Arage-Kikurage (boiled): 1.7 mg
   • Matsutake (raw): 1.3 mg
   • Honshimeji (raw): 1.1 mg
   • Winter Mushroom (raw): 1.1 mg
   • Winter Mushroom (boiled): 1 mg
   • Common Mushroom (canned in brine, solids): 0.8 mg
   • Nameko (canned in brine): 0.8 mg
   • Tamogitake (raw): 0.8 mg
   • Winter Mushroom (bottled in seasoning): 0.8 mg
   • Oyster Mushroom (boiled): 0.7 mg
   • Oyster Mushroom (raw): 0.7 mg
   • Nameko (raw): 0.7 mg
   • Kikurage (boiled): 0.7 mg
   • Usuhiratake (raw): 0.7 mg

Nuts and Seeds

Nuts and seeds serve as excellent plant-based sources of iron.

• Macadamia Nuts: 3.5 mg per cup dry roasted (43% of RDA)
• Almonds: 5.3 mg per cup whole (66% of RDA)
• Pine Nuts: 7.5 mg per cup dried (93% of RDA)
• Cashews: 7.8 mg per cup whole (97% of RDA)
• Flaxseeds: 9.6 mg per cup whole (120% of RDA)
• Pumpkin Seeds: 11.4 mg per cup dried (140% of RDA)
• Sesame Seeds: 21 mg per cup dried (262% of RDA); 1.3 mg per 2 tablespoons of tahini (16% of RDA)

Fruits

• Mulberries: 2.6 mg per cup (32% of RDA)
• Prune Juice: 2.9 mg per cup (36% of RDA)
• Black Olives: 8.5 mg per cup raw (100% of RDA)

Whole Grain Foods

• Oats: 1.2 mg per cup cooked (15% of RDA)
• Quinoa: 2.8 mg per cup cooked (35% of RDA)
• Spelt: 3.7 mg per 100 g flour (46% of RDA)
• Amaranth: 5.2 mg per cup cooked (65% of RDA)
• Cheerios Breakfast Cereal: 8.1 mg per cup (100% of RDA)
• Special K Breakfast Cereal: 8.7 mg per cup (108% of RDA)

Other Foods

Certain foods do not fit neatly into one of the aforementioned categories but are still rich in iron.

• Dried Thyme: 1.2 mg per teaspoon dried (15% of RDA)
• Blackstrap Molasses: 1.9 mg per 2 tablespoons (23% of RDA)
• Dark Chocolate: 3.4 mg per ounce (42% of RDA)
• Canned Coconut Milk: 7.5 mg per cup (93% of RDA)

Iron in Plants: Extracting from the Soil

Plants primarily acquire iron from the rhizosphere, the layer of soil that surrounds their roots. Although iron is one of the most abundant metals in the Earth's crust, its availability to plant roots is very low due to its tendency to form insoluble ferric oxides in aerobic or high pH soils. To cope with iron deficiency, plants have developed two main strategies: reduction-based and chelation-based.

1. Reduction-Based Strategy: Non-graminaceous plants, such as Arabidopsis thaliana, employ a reduction-based strategy. Protons are exuded into the rhizosphere by H+-ATPases, which lowers the soil pH and makes iron more soluble. The ferric chelate reductase then reduces Fe3+ to Fe2+, which is transported into the root epidermal cells by the divalent metal transporter IRT1.

2. Chelation-Based Strategy: Grasses, on the other hand, depend on the chelation-based strategy. They release phytosiderophores (PS) that bind Fe3+, forming Fe-PS complexes that are then transported back into the roots. This strategy is less sensitive to soil pH changes and is particularly effective in alkaline soils.

How to Increase Iron Absorption from Plant Foods

To maximize the absorption of non-heme iron from plant foods, consider the following strategies:

1. Eat Vitamin C-Rich Foods: Consuming vitamin C-rich foods alongside iron-rich plant foods can enhance iron absorption.
2. Avoid Coffee and Tea with Meals: These beverages can inhibit iron absorption.
3. Soak, Sprout, and Ferment: These processes can reduce phytates in grains and legumes, improving iron absorption.
4. Use a Cast Iron Pan: Cooking with cast iron cookware can increase the iron content of food.
5. Consume Lysine-Rich Foods: Legumes and quinoa, rich in lysine, can boost iron absorption.

Everything Starts With The Rocks

From its ancient geological formation to its critical biological functions, iron exemplifies the interconnectedness of Earth's processes and human health. By incorporating iron-rich foods into our diets, we bridge the gap between our planet's rich resources and our body's essential needs.

As we reflect on the journey of iron from the Earth's crust to our plates, it’s worth considering: How mindful are you of your iron intake? Do you think you’re getting enough of this essential mineral in your diet? Take a moment to evaluate your eating habits and the choices you make each day. Could a greater awareness of iron's importance inspire a change in your dietary practices?

Share your thoughts and start a conversation about how we can all ensure our bodies receive the vital nutrients they need to thrive.