Dante Carrillo
Iron deficiency is a common problem, especially for vegetarians and vegans, who are at a higher risk of developing it. Iron absorption is influenced by the foods we eat, and certain dietary compounds can inhibit or enhance the process. This is important to consider when planning vegetarian diets, as the bioavailability of iron from plant sources is lower than that of animal sources due to dietary inhibitors.
| Characteristics | Values |
|---|---|
| Inhibitors of iron absorption in vegetarian diets | Phytates, polyphenols, tannins, proteins from soy beans, milk, eggs, calcium, oxalates |
| Phytates found in | Cereals, grains, legumes, nuts |
| Polyphenols found in | Plants, teas, vegetables, fruits, some cereals, legumes, wine |
| Tannins found in | Tea, coffee |
| Calcium found in | High-calcium supplements, calcium-rich foods |
| Oxalates found in | Spinach, silverbeet, beetroot leaves, some green leafy vegetables |
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Phytates in plants
Phytates, also known as phytic acid, are a type of organophosphorus compound produced in terrestrial ecosystems by plants. They were first discovered in 1855 by German researcher Theodor Hartig, who identified circular particles in different plant seeds. Phytates are found in numerous plants and their parts, including seeds, nuts, legumes, and cereals. They are particularly prevalent in cereal grains.
Phytates are the principal storage form of phosphorus in plants, accounting for 60-80% of total phosphorus. They serve as a source of energy and antioxidant capacity for plants. However, in humans, they can impair the absorption of important minerals such as iron, zinc, and calcium, leading to potential mineral deficiencies. This is especially true for those who consume high phytate foods in most of their meals and those who follow vegetarian or vegan diets, as plant-derived iron is already poorly absorbed.
The phytate content of specific foods may vary depending on factors such as the location from which the food is sourced, agricultural management practices, and the use of food processing techniques. Certain preparation methods, such as milling of cereals, cooking, fermentation, and moistening, can significantly reduce the phytate content of foods.
Phytase, a phytate-degrading enzyme, has been proposed as a solution to degrade phytates and increase mineral bioavailability. Phytase supplementation has been successfully used in animal feed to improve the bioavailability of phosphorus and reduce the excretion of phytate-bound phosphorus.
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Calcium
In terms of vegetarian diets, the impact of calcium on iron absorption may be less pronounced. Research indicates that calcium supplements are unlikely to significantly affect iron balance unless calcium consumption is consistently very low. Additionally, the body has its own regulatory mechanisms to maintain iron balance, and iron toxicity from food sources is rare. Nevertheless, it is generally recommended to avoid consuming high-calcium foods or supplements with iron-rich meals to maximize iron absorption.
Vegetarians may have a higher risk of iron deficiency due to the lower bioavailability of iron from plant sources compared to animal sources. However, this risk is influenced by various factors, including individual dietary choices, intestinal adaptation, and the presence of other enhancers or inhibitors of iron absorption in the diet. While calcium may play a role in inhibiting iron absorption, it is just one of several factors that can impact overall iron status in vegetarians.
To ensure adequate iron intake and absorption, vegetarians can focus on including a variety of iron-rich plant foods in their diet, such as lentils, beans, tofu, nuts, seeds, and dark leafy greens. They can also enhance iron absorption by consuming vitamin C-rich foods alongside their meals. While calcium-rich foods should ideally be consumed separately from iron-rich meals, it is important to note that calcium is a vital nutrient that should be included in the diet at appropriate levels.
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Animal proteins
Vegetarians and vegans have a low body iron status, with women in the reproductive age group being particularly susceptible to iron deficiency. The total amount of iron available from a vegetarian diet is estimated to be around 10%, while a mixed diet including meat provides about 18% of iron. This discrepancy is attributed to the lower bioavailability of iron from plant sources and the presence of inhibitors.
However, recent studies suggest that dietary composition is not the only factor influencing iron status. For example, menstrual blood loss is a significant contributor to low iron stores in women. Additionally, a 2021 study found that after eliminating inflammation, vegetarians had a similar prevalence of iron deficiency as those following an omnivorous diet.
To enhance iron absorption, it is recommended to include vitamin C-rich foods in meals, as vitamin C can increase iron absorption by up to sixfold. Vitamin A and beta-carotene also play a crucial role in maintaining healthy iron levels.
In summary, while animal proteins can impact iron absorption, the overall iron status of an individual depends on various factors, including diet, physiological conditions, and the presence of enhancers or inhibitors of iron absorption.
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Polyphenols in plants and teas
Polyphenols are found in various amounts in plant foods and beverages, including vegetables, fruits, some cereals and legumes, tea, coffee, and wine. They are natural plant compounds that inhibit iron absorption. Tea, for example, is one of the most popular beverages worldwide, with about three billion kilograms consumed annually. Tea is brewed from the plant Camellia sinensis and consumed as green, black, or oolong tea.
Polyphenols in tea include catechins, theaflavins, tannins, and flavonoids. Catechins constitute about 25% of the dry mass of a fresh tea leaf, and the content varies depending on species, growing location, season, light variation, and altitude. Catechins include epigallocatechin-3-gallate (EGCG), epicatechin (EC), epicatechin-3-gallate (ECG), and epigallocatechin (EGC). EGCG is the major catechin in tea and may account for 50-80% of the total catechin content. Catechins are the largest type of flavonoids in growing tea leaves, and they have been shown to inhibit the absorption of non-heme iron.
Green tea contains flavanols such as kaempferol, quercetin, and myricetin, and has a higher content of EGCG than other teas. Catechins in green tea can account for 30-42% of the dry weight of the solids in brewed tea. Black tea, on the other hand, undergoes enzymatic transformation during production, resulting in the oxidation and polymerization of catechins. The approximate composition of black tea includes catechins (10-12%), theaflavins (3-6%), thearubigins (12-18%), flavonols (6-8%), phenolic acids (10-12%), and more. Oolong tea, which is partially fermented, contains a minor component called 3'-O-methyl-EGCG.
While polyphenols inhibit iron absorption, vitamin C enhances it. Vitamin C captures non-heme iron and stores it in a form that the body can absorb more easily. Foods rich in vitamin C include citrus fruits, dark green leafy vegetables, bell peppers, melons, and strawberries.
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Oxalic acid
Vegetarians and vegans are at a higher risk of developing iron deficiency due to the lower bioavailability of iron from plant sources compared to animal sources. This is partly due to dietary inhibitors such as phytate in plants. Phytate is the principal iron absorption inhibitor found in grains, especially whole grains, legumes, and nuts. It is estimated that more than 50% of phytate intake comes from grain products, which are a significant part of many vegetarian diets.
Other dietary factors that can influence iron absorption include polyphenols, calcium, and ascorbic acid (vitamin C). Polyphenols are found in various plant foods and beverages, including vegetables, fruits, some cereals, legumes, tea, coffee, and wine. Calcium has been considered an inhibitor of both haem and non-haem iron absorption, but recent research suggests that its effect on iron absorption over a long period of time is limited. Vitamin C, on the other hand, is known to enhance iron absorption. It can increase absorption by up to sixfold, particularly in those with low iron stores, by facilitating the conversion of iron into a form that the body can more easily absorb.
To optimize iron absorption, it is recommended to include vitamin C-containing vegetables in meals, especially in vegetarian and vegan diets. High-calcium supplements should also be avoided during meals, and calcium-rich foods should be consumed during meals with the lowest iron content.
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Frequently asked questions
Phytate, a compound found in plant-based diets, is the most significant inhibitor of iron absorption in vegetarian diets.
Other inhibitors include polyphenols found in tea, coffee, wine, legumes, cereals, fruits, and vegetables. Calcium is also an inhibitor, although its effect is limited over a long period.
Phytate demonstrates a dose-dependent effect on iron absorption, meaning that higher amounts of phytate in a diet will result in lower iron absorption.
Inhibitors of iron absorption can contribute to iron deficiency, which can lead to anemia. Vegetarians and vegans are at a higher risk of iron deficiency due to lower bioavailability of iron from plant sources.
Vegetarians can improve their iron absorption by including vitamin C-rich foods in their meals, such as citrus fruits, dark green leafy vegetables, and bell peppers. Vitamin C enhances iron absorption by up to sixfold.
