The absorption and utilization of iron are complex processes influenced by various factors, including the form of iron consumed, co-factors, inhibitors of absorption, and solubility/storage. One of the primary factors influencing iron absorption is the form in which iron exists within the two biological structures when consumed: heme (Fe2+/ferrous) found in animal products and non-heme (Fe3+/ferric) iron found in plants (Hyams & Kay, 2021). (Note, plants can also contain some ferrous iron, although it is not heme iron). Heme iron, found in animal-based foods, is more easily absorbed and immediately utilized by the body. Non-heme iron is less easily absorbed and counterintuitively is preferred by the body as will be elucidated below.
Find a great video on a high iron dish: spinach fritters.
Factors Inhibiting Iron Absorption
Iron absorption is influenced by various factors. The type of iron consumed is critical, as absorption rates differ significantly between heme (animal-based) and non-heme (plant-based) iron sources. Non-heme iron absorption is lower due to compounds like fiber, phytates, and polyphenols that occur concurrently found in plant foods. A lack of certain vitamins can also inhibit absorption, release, or uptake of iron.
Fiber
Fiber can interfere significantly with iron absorption. For example, in fava beans, iron bioavailability remains low even after soaking to remove phytates due to their high fiber content. This can be good or bad depending on the iron levels you are consuming, because iron is one of those nutrients that can damage the body when it is presented in too high amounts.
Riboflavin Deficiency
Riboflavin deficiency can reduce iron absorption as well as iron utilization. Therefore, it is beneficial to consume riboflavin-rich foods alongside iron sources to enhance absorption (Powers, 2003). Keep in mind that if you are taking an iron supplement but not getting enough riboflavin from foods like grapes, mushrooms, yogurt, and buckwheat, your blood cells may not respond as effectively as when you include these foods or a riboflavin supplement alongside your iron containing foods. While the available data is limited, animal studies indicate that riboflavin deficiency can decrease iron absorption in animals and reduce iron utilization in adult men, whereas riboflavin supplementation has shown positive effects on hemoglobin levels (Fairweather-Tait et al., 1992). Furthermore, anemia has been linked to riboflavin deficiency, so if your tests indicate anemia, consider increasing your intake of dark leafy greens and incorporating mushrooms as a dietary staple. You can enhance the riboflavin (and vitamin D) content of your mushrooms by exposing them to sunlight for a day.
It is important to realize that if you have low riboflavin levels you need even more iron to prevent anemia. But you should not justify your low riboflavin intake with a higher iron intake because this causes oxidative stress in the body. Therefore, a more effective strategy to prevent anemia is to increase your riboflavin intake. This does not have negative or oxidative effects on the body in the same way iron can, and riboflavin is water soluble so higher levels can be excreted. There are simple ways to increase riboflavin levels through food. For example, a glass of soy milk can increase riboflavin intake by 0.05 mg to 0.5 mg, depending on the soy milk. Homemade soymilk is cheap and takes minutes to make, simply blend 4 cups of water with ¼ c of cooked soybeans. Straining is optional.
Vitamin A Deficiency
When you are deficient in vitamin A you may not be able to pull out iron out of it’s stores in the fat cells (IOM et al., 2006). This can negatively affect hemoglobin. This is one reason why a food like spinach, which is high in both vitamin A and iron, is a better choice for your nutrients than a meat source of iron. You should consume at least one serving of foods like carrots, sweet potatoes, winter squashes, and carrot and/or beet juice on a daily basis. Orange fruits like cantaloupe are also high in vitamin A.
Find a very simple soup recipe that is high in vitamin A and riboflavin here: https://www.youtube.com/watch?v=VDFqAYXtGzY
Or another extremely easy recipe high in both these nutrients is Kabocha Squash Soup with Oyster Mushrooms;
Caffeine
Caffeine, especially from chronic intake during breastfeeding, can reduce the availability of iron in breast milk (IOM et al., 2019). One cup of coffee a day or 200- 300 mg/day is considered safe during lactation. Pregnant women should take greater care to avoid caffeine because the half-life of caffeine increases from 3-4 hours to 9-10 hours during pregnancy. This means that when you are pregnant it takes your body 10 hours to remove half the cup of coffee (caffeine) from your body. After that it is another 10 hours before half of that previous amount is removed, aka one quarter of the original amount of caffeine. This translates to a cup of coffee that you consume at 8 am is only halfway removed from your system at 6 pm, and by 4 am is only 75% removed. This is a good reason, if just for your sleep quality, vital for growing a baby, to abstain from caffeine unless absolutely necessary on a rare occasion. Your baby is completely dependent upon you for clearing (or removing substances) from your body and because it takes so long for caffeine to be removed from your system it should be indulged in on only those rare occasions such as you have an important brief to finish, or a master’s thesis to finish revising by that night.
Phytates
Phytates are prominent inhibitors of iron absorption and are a primary reason why some vegetarians with a balanced diet might still experience iron deficiency (Sandberg, 2002). However, it’s important not to vilify phytates entirely, as they also offer numerous health benefits, such as cancer prevention. The extent to which phytates can be reduced varies depending on the type of bean or grain, and if you are cooking at home as a vegetarian and using proper methods of soaking and germination, there is no reason you cannot obtain enough iron from high phytate foods.
Soaking and germination can reduce phytate levels in foods like brown rice, cowpeas, faba beans, black beans, and chickpeas. Using these techniques, brown rice can have 40-90% of phytates removed (Liang et al., 2008). Cowpeas/black-eyed peas exhibit a reduction of 20% through soaking and up to 50% through germination (Sinha & Kawatra, 2003). Faba beans/broad beans experience phytate removal of 36-51% via soaking and 40-80% through fermentation. For black beans (and other Phaseolus vulgaris), soaking them in room temperature water at a neutral temperature results in an 88% reduction in phytates (Sandberg, 2002). Chickpeas, on the other hand, only see a modest 4% reduction through germination but achieve nearly 60% removal when boiled, the most common preparation method (Mittal et al., 2012).
Science has acknowledged since 1953 that a 5-day germination period for lentils can result in the removal of 53% of phytates (Vidal-Valverde, 1994). These processes also entail a reduction in the polyphenol content of legumes and grains. Subsequent to a substantial portion of phytates being eliminated through soaking or sprouting, further reductions of up to 97% can be achieved through boiling or canning. Consequently, traditional soaking and cooking methods effectively counter the argument that legumes are inadequate sources of iron due to diminished bioavailability caused by phytates.
Fermentation or germination of legumes and grains consistently proves effective in removing up to 96% of phytates. These methods also provide flexibility in your cooking routine. You can soak your grains or beans overnight, drain them the next day, and then cover them with a towel. At this point, you have the option of using them in various dishes over the next 2-5 days. If you reside in a warm and/or dry climate, you may need to rinse them every 24-48 hours to continue the germination process and prevent spoilage. Alternatively, you can put them in the fridge until you are ready to cook. Additionally, these methods increase the protein content of your beans and grains and reduce their gassiness
Ferritin
Ferritin, the form of iron in legumes, is a large complex of iron and oxygen molecules. It is taken up much more efficiently than single iron ions (found in meat) and is taken up by receptor-mediated endocytosis. Ferritin is resistant to phytate interference (Ettinger, 2016). Therefore, the argument that you cannot consume plant based iron due to phytates is invalid.
Polyphenols
Polyphenols, found in tea and dairy milk, can inhibit iron absorption (Zijp et al., 2000). Legumes also contain polyphenols but these are removed by soaking and to a greater extent by germination. Berries are another food that are high in polyphenols. These polyphenols have a tremendous quantity of health benefits on their own. Some of these benefits are decreased inflammation and antioxidant effects which necessitate the intake of polyphenols for an optimal pregnancy.
Consumption of foods rich in polyphenols, such as tea and dairy milk, is prevalent in the general population (Zijp et al., 2000). However, it’s important to note that polyphenols, while beneficial in many ways, can inhibit iron absorption (Zijp et al., 2000). Conversely, legumes, which also contain polyphenols, undergo processes like soaking and germination, effectively reducing these compounds. Additionally, berries, renowned for their health benefits, boast high levels of polyphenols, which contribute to decreased inflammation and antioxidant effects, making them particularly advantageous during pregnancy. This underscores the necessity of balancing polyphenol intake with the nutritional requirements for plenty of plant based iron for an optimal pregnancy.
There are many ways to be conscious of how you are eating to maximize nutrient intake by separating your consumption of polyphenol containing foods with iron containg foods. For instance, if you have switched from coffee to a steaming mug of black tea with homemade hemp milk and honey in the morning, wait an hour before your iron-rich breakfast of eggs, sweet potato and spinach (Ahmad Fuzi et al., 2017), and if you’re lucky, lentil sausage patties.
For a breastfeeding mother, this should be easy when you have a boogy boo who wants the milkies for a second time by 9 am and needs a diaper change in the middle of cooking your sweet potatoes. Just cover your pan and put it on low, adding a bit of water if you need more time to prevent burning your sweet potatoes. By the time you come back your tea will be digested and breakfast ready! If you’re having berries as a course of your dinner, elect to consume them while you are preparing your spinach saag paneer and white beans, which you plan to eat much later after your butterball has gone to bed. Another intelligent alternative is to consume berries alongside your steak to lower your absorption of iron from meat. This is particularly important because when your body receives higher quantities of heme iron than it currently requires, it can lead to oxidative stress and inflammation.
Positive Effects of Iron Bioavailability Inhibitors
The advantages of consuming beans/nuts, with their fiber, phytates, and polyphenols, far outweigh their inhibitory effects, offering substantial benefits to your microbiome, immune system, folate intake, plant protein intake, and antioxidant effects. Both polyphenols and phytates have demonstrated their ability to hinder the initiation or progression of cancer. Notably, the inositol found in beans, a type of phytate, has been proven to prevent the peroxidation of hydroxy radicals generated from iron, thus protecting lipids in your body from oxidation. In simpler terms, this means that phytates in beans also act as powerful antioxidant (SATHE & VENKATACHALAM, 2001). Moreover, phytates exhibit the potential to impede the development of osteoporosis and might even emerge as a new essential nutrient (Bačić et al., 2010).
Seeds, despite containing phytates and polyphenols, constitute a vital food group due to their rich mineral and vitamin content, healthy fats, and plant protein. They are a source of essential omega-6/3 fats and contribute to better blood sugar stability compared to many other foods. Maintaining stable blood sugar levels is especially crucial during pregnancy to prevent morning sickness and the development of glucose metabolism issues like gestational diabetes. Among seeds, sesame seeds, pumpkin seeds, and chia seeds stand out as some of the highest iron sources. Cashew nuts also offer similar advantages to seeds and are notable for their high iron content.
Foods and Factors That Enhance Absorption
Vitamin C
Iron absorption is enhanced when you consume foods rich in Vitamin C or acids alongside iron-containing foods, particularly for plant based iron sources. For instance, adding a squeeze of lemon to your iron-rich spinach or serving red bell peppers alongside it can increase the bioavailability of iron for absorption in your body (Whittaker, 1998).
Other Compounds
There are other compounds found in certain foods that can enhance iron absorption. These include malic acid, which is found in apples and pears, as well as lactobacillic acid, which is present in fermented or cultured vegetables. Animal studies have demonstrated that consuming an adequate amount of riboflavin can promote the mobilization of iron from the gastric mucosal lining into the body. For those interested in the chemistry behind it, this phenomenon occurs because iron needs to be reduced for absorption, and riboflavin (FAD) acts as a reducing agent (Powers, 2003). This is why acidic substances like ascorbic acid (Vitamin C) are known to increase iron absorption. Therefore, consider incorporating organic soy foods, spinach, leafy beet greens, and almonds into your daily diet for their potential to enhance iron absorption from their riboflavin content.
Interaction with Other Minerals
Zinc, iron, and copper are integral to various physiological functions, and their interactions often intersect, impacting nutrient absorption and overall health (Grzeszczak et al., 2020). Notably, copper and zinc compete for absorption in the body, with imbalances potentially leading to adverse pregnancy outcomes health (Grzeszczak et al., 2020). Furthermore, zinc and iron engage in competitive interactions during intestinal absorption, particularly when iron intake exceeds that of zinc, although this typically becomes significant when the iron intake significantly exceeds that of zinc, often in ratios like 2:1 or 3:1 (iron: zinc). If this is the case then the absorption of zinc becomes limited. This underscores the importance of maintaining balanced nutrient ratios, especially during pregnancy. If you consume a plant focused omnivore diet free of processed foods during pregnancy your nutrient ratios should naturally come out balanced.
In addition to these interactions, zinc also interacts with vitamin D and calcium and affects their functionality or uptake, respectively. This shows the interconnectedness of nutrient absorption and how if you lack one nutrient this can have a functional effect on others. This holistic understanding contributes to our grasp of the intricate balance essential for optimal health during pregnancy and lactation, aligning with the broader themes explored in this book on maternal nutrition.
Placental Regulation
The placenta plays a critical role in regulating iron uptake from the mother to the fetus through various mechanisms, some of involving transferrin, an iron uptake protein, while others do not. However, if both the mother and fetus are deficient in iron, the placenta cannot increase its iron uptake capacity. This is not always the case, for example, for of DHA (Docosahexaenoic acid), there is a distinct pattern where the placenta can enhance the relative uptake from the mother when her DHA levels are low.
It’s important to note that the placenta lacks mechanisms to shield the fetus from excess iron in the mother’s bloodstream. Therefore, maintaining an appropriate balance in iron consumption is crucial, as both excessive and inadequate intake of iron-containing foods can have implications for fetal development. Excess iron intake occurs when the iron storage capacities of the body, or the molecules ferritin and hemosiderin, are saturated. These molecules store iron in the Fe3+ form which is non-heme or ferric form.
Solubility
In addition to considering the type of iron consumed and the factors that influence its absorption, it’s important to take into account the fat solubility of iron. Unlike water-soluble minerals/vitamins, which need to be consumed daily as any excess is swiftly excreted through the kidneys, fat-soluble minerals and vitamins can be consumed less frequently. As their name implies, fat-soluble nutrients are stored in the body’s fat tissues and can persist for extended periods.
This characteristic is advantageous for certain fat-soluble nutrients like DHA, Vitamin D, and Vitamin E because, when sourced from food, they are not toxic even at their upper limits. The benefit of fat-soluble minerals or vitamins lies in the body’s ability to absorb larger amounts within a short timeframe, ensuring a reserve for days when dietary intake may be insufficient. This ensures that both you and your baby receive essential nutrition, even during brief periods of dietary inadequacy.
However, the drawback of iron’s fat solubility, particularly heme iron from animal-based sources, is that it can be stored in excess of the body’s requirements.
Read more about iron and supplementation here: https://thecarmencooks.com/staging/3924/plant-based-iron-do-you-need-a-supplement-like-floradix-liquid-iron-or-should-you-employ-other-strategies/
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