Leafy Green Vegetables and Iron Absorption

Overview

We all know that leafy green vegetables are considered to be nutritious and an important part of a healthy diet, but what role do they play in iron and its absorption?

Well, they are a nutritional powerhouse, containing various nutrients, including iron - though, it is important to note that it is a non-heme type of iron, as we will discuss. We will also discuss the importance of iron, how it is absorbed and the factors that affect it. Additionally, we will look at ways to improve the absorption of iron from your diet, which is important especially if you have a plant-based diet.

Importance of iron in the human diet

Iron is an important nutrient, as it plays a pivotal role in several biological processes within the human body. These include oxygen transport around the body, division and differentiation of cells, and electron transport within cells.¹ Within the body, iron binds to proteins, forming heme complexes and enzymes, such as haemoglobin and myoglobin as well as non-heme enzyme complexes like transferrin and ferritin.⁴

The majority of the iron in the body is found in haemoglobin, a heme enzyme complex, responsible for carrying oxygen throughout the body. The rest is found in other body tissues such as myoglobin in the muscles, transferrin in the blood, and ferritin iron stores in the bone marrow.² The balance of iron within the human body depends highly on how it is absorbed, as there is no exact mechanism of removing it from the body, although a small amount is lost in urine, bile and from skin and intestinal cells.⁴

Therefore, it is important to highlight the iron content of various food sources and how they are absorbed in the body.

Understanding iron absorption

Explanation of heme and non-heme iron

Iron consumed from food is digested and absorbed in the intestine. The amount absorbed varies depending on certain factors, like the type of iron.⁴ There are two classifications of the iron from food sources: heme or non-heme. Sources of heme iron are animal-based, including poultry, fish and meat. Whereas non-heme sources are mainly plant based, such as leafy green vegetables like spinach and kale, legumes like peas and beans, and seeds and nuts.⁵ 

A major difference between heme and non-heme iron is the bioavailability in the body following consumption. The term “bioavailability” refers to the amount of nutrient extracted from consumed food and available for use in the body.⁶ Heme iron is considered to have higher bioavailability than non-heme iron, because the mode of absorption is different. Non-heme iron absorption is more tightly controlled than that of heme iron and is affected by the presence of other nutrients or substances in the diet.⁷

Factors affecting iron absorption

Enhancers of iron absorption

1.) Vitamin C: This nutrient is found in various fruits and vegetables, including oranges, kiwis, and potatoes. It is known to improve the absorption of non-heme iron, making it a crucial factor in iron absorption of vegetarians. This is achieved by forming a chelate - a complex compound formed when a molecule tightly grips a metal ion - with the iron, thus facilitating the chemical state of iron that is more absorbable in the gut.¹

2.) Meat: Diet containing fish, meat or poultry enhances the absorption of non-heme iron from plant-based sources. The exact reason is not entirely clear; however, it is thought that the presence of meat blocks the factor that prevents non-heme iron absorption.¹ 

Inhibitors of iron absorption

1.) Phytates and fibre: Found in whole grains, nuts, and seeds, phytates can reduce iron absorption because they form a complex chelate with iron, making it unabsorbable.¹ Food preparation methods like soaking and fermentation have been found to reduce the phytate content, thus reducing the inhibitory effect on iron absorption.^6,7

2.) Calcium: While calcium is essential for bone health, high levels of calcium in the diet, particularly from supplements, may prevent the absorption of both heme and non-heme iron.⁶

3.) Polyphenols: Found in black and herbal teas, coffee, red wine, spices like turmeric, some vegetables and legumes.⁶ Polyphenols hinder the absorption of iron in a similar way to phytates by chelating it and rendering it unavailable for absorption in the gut.¹

Nutritional value of leafy green vegetables

Types of leafy green vegetables 

Leafy green vegetables encompass a wide range of vegetables, each containing various nutrients. Some of the most popular ones are spinach, kale, lettuce, and collard greens. They are known to be an essential part of a healthy diet due to the nutritional value they provide. Leafy green vegetables are also quite versatile, as some can be eaten raw, such as in salads, or cooked as part of a meal. 

Nutrient content in leafy greens

Leafy greens are rich in micronutrients like vitamin K, B6 and C, minerals like iron, magnesium and potassium, and fibre. They also contain special components like phytochemicals and flavonoids.⁹ These all play several important roles in the body, collectively helping prevent illness, boost the immune system and promote overall good health.¹²

1.) Iron content

Leafy green vegetables are known to be a good plant-based source of iron. The absorption of this iron differs from how it is absorbed from other non-plant based sources.¹ This is because it is non-heme type iron, and the absorption of this type of iron is more likely to be affected by the presence of other nutrients such as fibre.⁷

2.) Other nutrients 

In addition to iron, leafy greens provide a number of other nutrients crucial for overall health. One such nutrient is vitamin C, which not only acts as an antioxidant but also aids in the absorption of non-heme iron. Consuming leafy greens alongside vitamin C-rich foods can optimise the body's ability to absorb iron efficiently.¹

Furthermore, these greens are often abundant in folate, a B-vitamin essential for DNA synthesis and cell division. It is particularly crucial during periods of rapid growth, such as pregnancy. Leafy greens like kale and collard greens contribute significantly to meeting daily folate requirements.¹⁰

Dietary strategies to optimise iron absorption

Having explored the intricate mechanisms of iron absorption with leafy green vegetables, it iss time to translate this knowledge into practical dietary strategies. By incorporating these strategies into your daily meals, you can enhance the bioavailability of iron from leafy greens and support overall nutritional well-being.

Combining leafy greens with iron-rich foods

To maximise iron absorption from leafy greens, consider combining them with other iron-rich foods. Pairing vegetables like spinach or kale with legumes, tofu, or seeds can provide a synergistic effect, as these foods contribute additional sources of non-heme iron. This can be particularly beneficial for individuals who rely on plant-based sources of iron. Meat, fish, and poultry can also be paired with leafy greens, as these sources of heme iron can enhance the absorption of non-heme iron, as discussed earlier. Including a variety of iron-rich foods in your meals creates a balanced and nutrient-dense plate, ensuring a steady supply of this essential mineral.

Pairing leafy greens with vitamin C sources

As highlighted earlier, vitamin C plays a pivotal role in enhancing the absorption of non-heme iron. Incorporating vitamin C-rich foods into meals containing leafy greens can significantly improve iron bioavailability. Simple strategies include adding citrus fruits, bell peppers, or tomatoes to your salads, or enjoying a glass of orange juice with your iron-rich leafy green dishes.

Meal planning for improved iron absorption

Strategic meal planning is a powerful tool for optimising iron absorption. Consider incorporating a variety of nutrient-dense foods into your meals to ensure a well-rounded intake of essential nutrients. Including sources of vitamin C and iron-rich foods within the same meal, along with properly cooked leafy greens, can create an iron-friendly environment for absorption.

Cooking methods that influence iron bioavailability

The preparation of leafy greens also plays a crucial role in determining the bioavailability of iron. While raw vegetables are often praised for retaining their nutritional content, cooking leafy greens can enhance iron absorption. Cooking breaks down cell walls and fibres, making the nutrients more accessible for absorption.¹¹ It can also help reduce the impact of phytates and oxalates (which are iron inhibitors) on iron absorption.¹³ Steaming, sautéing, or boiling leafy greens can be effective methods to improve iron bioavailability while preserving the overall nutritional value of these vegetables.

Special considerations and recommendations for a balanced diet

As we navigate the strategies to optimise iron absorption from leafy greens, it is essential to address special considerations and offer recommendations for maintaining a balanced and health-conscious diet. Whether you are exploring a plant-based lifestyle or seeking to diversify your nutrient intake, these insights will help guide your dietary choices.

• For individuals following vegetarian or vegan diets, obtaining sufficient iron can be achieved by embracing a variety of plant-based iron sources. As discussed, combining leafy greens with other iron-rich plant foods is a practical approach. Additionally, exploring alternative sources of non-animal iron, such as fortified cereals and legumes, can contribute to meeting daily iron requirements
• If you suspect or have been diagnosed with iron deficiency, it is crucial to consult with a dietician. While incorporating iron-rich foods into your diet is a positive step, supplementation may be recommended in certain cases to meet specific needs. However, self-prescribing iron supplements without professional guidance can lead to adverse effects, emphasising the importance of personalised advice
• Maintaining a balanced diet involves more than just focusing on a single nutrient. While leafy greens offer valuable iron and other essential nutrients, it is crucial to diversify your food choices to ensure a broad spectrum of vitamins and minerals. Incorporating a rainbow of fruits, vegetables, whole grains, and lean proteins contributes to overall health and provides a wide array of essential nutrients

Summary

• Iron is a beneficial mineral in the human body because it forms part of several enzymes and molecules that play important functions such as oxygen transport
• There are two types of iron: heme and non-heme. Leafy green vegetables are a source of non-heme iron, which is not easily absorbed in the gut
• The absorption of non-heme iron is influenced by the presence of other nutrients that either enhance or prevent iron absorption
• The nutritional value of leafy green vegetables is not limited to iron, but they contain other nutrients such as vitamins and fibre
• Certain strategies like pairing leafy greens with vitamin C rich foods, cooking leafy greens, and planning meals are useful to consider to improve the absorption of iron from your diet, especially if your diet is plant based
• Maintaining a balanced diet rich with various foods is necessary for overall health