Is heme iron only found in animals?

December 7, 2025 •

4 min read

While many believe heme iron is exclusive to animal sources, it's a matter of biological classification, not dietary restriction, to understand its origin. All dietary iron exists in two forms—heme and non-heme—with heme iron being found in animal flesh like meat, poultry, and seafood.

Quick Summary

Heme iron originates in animal flesh like meat, fish, and poultry and is more easily absorbed by the body. The less bioavailable non-heme iron comes from plants and fortified foods.

Key Points

Exclusively Animal-Based: Heme iron is naturally found only in animal flesh, including meat, poultry, and seafood, not in plants.
High Bioavailability: The body absorbs heme iron much more efficiently and consistently than non-heme iron, with fewer dietary inhibitors interfering with the process.
Non-Heme Iron is Widespread: The other form, non-heme iron, is present in all plant foods, as well as in eggs and dairy.
Absorption Can Be Managed: The bioavailability of non-heme iron can be greatly enhanced by consuming it with a source of Vitamin C and minimized by avoiding inhibitors like coffee, tea, and phytates at mealtime.
Vegan Alternatives Exist: While not natural plant sources, some plant-based meat substitutes contain lab-grown heme iron produced from genetically engineered yeast.
Strategic Dieting Is Key: Whether you eat meat or not, understanding the differences between heme and non-heme iron and their absorption mechanisms is key to maintaining adequate iron status.

The Simple Answer: Yes, Heme Iron is Primarily Found in Animals

Yes, for all practical dietary purposes, heme iron is found only in animal flesh. This means sources like meat, poultry, and fish are the only foods that contain significant amounts of this highly bioavailable form of iron. In the context of a whole-food diet, there are no natural, plant-based sources of heme iron. The iron found in plant foods is exclusively non-heme iron, which has a different molecular structure and is absorbed less efficiently by the body.

The reason for this lies in the biological function of heme iron. It is an essential component of hemoglobin and myoglobin, the proteins responsible for carrying and storing oxygen in the blood and muscles of animals. When humans consume animal tissue, they also consume these proteins, from which the body can easily extract and absorb the heme iron.

Heme vs. Non-Heme: Understanding the Differences

Dietary iron is classified into two types: heme and non-heme. The key distinctions lie in their molecular composition, food sources, and how the body absorbs them.

What is Heme Iron?

Heme iron is an iron atom bound within a porphyrin ring, a complex organic molecule. This structure protects the iron from dietary factors that can inhibit absorption. The body absorbs heme iron through a separate, dedicated pathway in the small intestine, making its absorption more efficient and consistent than that of non-heme iron. Heme iron is found exclusively in animal tissue, including:

Red meats (beef, lamb, pork, venison)
Poultry (chicken, turkey)
Seafood (fish, shellfish, oysters, clams, mussels)
Organ meats (liver, spleen)

What is Non-Heme Iron?

Non-heme iron is found in both plant-based foods and animal products (the iron in eggs and dairy is non-heme). Unlike heme iron, its absorption is highly dependent on other dietary factors. It is more reactive and can be bound by inhibitors, like phytates, polyphenols, and calcium, which are common in plant foods. Its absorption rate is significantly lower than that of heme iron, and it relies on a different transport protein to enter the intestinal cells. Common sources of non-heme iron include:

Legumes (lentils, beans, chickpeas)
Nuts and seeds (pumpkin seeds, cashews)
Whole grains and fortified cereals
Dark leafy greens (spinach, kale)
Dried fruits (apricots, raisins)
Tofu and other soy products

Absorption: Why Heme Iron is More Bioavailable

The human body has evolved distinct mechanisms for absorbing heme and non-heme iron, which explains their different bioavailability. The term bioavailability refers to the proportion of a nutrient that is absorbed and used by the body. For heme iron, this is a highly efficient process. It is absorbed as an intact molecule through a specific transporter, largely unaffected by other foods consumed at the same time.

Non-heme iron, however, must be converted from its ferric ($Fe^{3+}$) state to its ferrous ($Fe^{2+}$) state before it can be absorbed. This process can be hindered by inhibitors, or enhanced by enhancers. Vitamin C, for instance, significantly boosts non-heme iron absorption, while compounds like phytates in grains and legumes, and tannins in tea and coffee, reduce it. This is why dietary context is so important for non-heme iron intake.

The "Meat Factor": Enhancing Non-Heme Absorption

Interestingly, the consumption of heme iron-containing foods can actually enhance the absorption of non-heme iron from other foods eaten in the same meal. This phenomenon, sometimes called the "meat factor," occurs when peptides or proteins from animal tissues help keep non-heme iron in a soluble form, thereby improving its uptake. However, this is not a substitute for having a well-balanced diet rich in diverse iron sources.

Are There Any Plant-Based Sources of Heme Iron?

Currently, no naturally occurring plant foods contain heme iron. However, some food companies have developed products that contain a form of heme iron that is produced via genetic engineering. This process involves using genetically modified yeast to produce leghemoglobin, a plant protein structurally similar to animal hemoglobin, which contains a heme group. While this lab-grown heme is technically not from an animal, it is not a naturally occurring component of any plant-based food.

Comparison Table: Heme vs. Non-Heme Iron


Feature	Heme Iron	Non-Heme Iron
Primary Source	Animal flesh (meat, poultry, fish)	Plants (legumes, grains, nuts), eggs, and dairy
Bioavailability	High (15-35% absorbed)	Lower (2-20% absorbed)
Absorption Pathway	Dedicated, less affected by diet	Competes with dietary inhibitors
Absorption Influencers	Few inhibitors, but can enhance non-heme absorption	Enhanced by Vitamin C; Inhibited by phytates, tannins, calcium
Molecular Form	Iron atom in a porphyrin ring	Ionic iron, highly reactive

Conclusion: The Importance of a Balanced Approach

In conclusion, the claim that heme iron is only found in animals is largely true in a natural, whole-food context. While innovations in food science have created lab-grown versions, the natural dietary sources are exclusively animal-based. Heme iron's higher bioavailability offers a significant advantage for iron absorption, especially for individuals with low iron stores. However, this does not mean plant-based diets are inadequate in iron. By strategically pairing non-heme iron sources with vitamin C-rich foods, and being mindful of absorption inhibitors, vegetarians and vegans can effectively meet their iron requirements. Understanding the distinct absorption mechanisms of both heme and non-heme iron allows for a more balanced and informed approach to nutrition, regardless of dietary preference. For more detailed information on dietary iron sources, visit the Harvard T.H. Chan School of Public Health website: The Nutrition Source.

Frequently Asked Questions

The primary difference lies in their source and bioavailability. Heme iron comes from animal sources and is more readily absorbed by the body, while non-heme iron comes from plants and has a lower absorption rate, which can be influenced by other dietary factors.

Heme iron is absorbed more easily because its molecular structure, an iron atom within a porphyrin ring, is taken up intact by specialized transporters in the intestine. This mechanism protects it from many dietary inhibitors that affect non-heme iron.

Yes, vegetarians and vegans can get enough iron by consuming a variety of non-heme iron-rich foods, including legumes, nuts, seeds, leafy greens, and fortified cereals. They can further enhance absorption by pairing these foods with vitamin C sources.

The best sources of heme iron are animal products, particularly red meat, organ meats like liver, and seafood such as clams, oysters, and fish.

Yes, consuming animal flesh, a phenomenon known as the "meat factor," can significantly enhance the absorption of non-heme iron from other foods eaten in the same meal.

Non-heme iron absorption is inhibited by several dietary factors, including phytates in whole grains and legumes, polyphenols in coffee and tea, and calcium in dairy products.

While heme iron is highly beneficial for iron status, high intake, particularly from red and processed meats, has been associated with an increased risk of certain diseases, such as colorectal cancer. However, these risks are often linked to factors beyond just the heme iron itself.

To maximize non-heme iron absorption from plant foods, pair them with a source of vitamin C (e.g., bell peppers with spinach). It's also recommended to consume coffee and tea between meals rather than with them, as they can inhibit absorption.