Summary
Many people around the world — particularly in lower-income countries — rely heavily on plant-based diets built around grains, legumes, and seeds. While these foods are nutritious, they contain a naturally occurring compound called phytate (or phytic acid) that acts as a significant barrier to absorbing two critical minerals: iron and zinc. Deficiencies in these minerals can lead to serious health consequences, including anemia, weakened immunity, and impaired growth and development, especially in children and pregnant women. This review paper, authored by nutrition researchers from New Zealand, the United States, and a children's research institute, examines the science behind phytate's impact on mineral absorption and what it means for how we set dietary guidelines and design nutrition programs globally.
What is phytate and why does it matter? Phytate is a compound found naturally in the outer layers of plant foods like wheat, rice, corn, beans, and lentils. It binds tightly to iron and zinc in the digestive tract, forming complexes the body cannot absorb. This means that even if a plant-based diet appears to contain adequate iron and zinc on paper, the body may only be absorbing a fraction of what's listed.
Key points from the review: Phytate is one of the most potent inhibitors of iron and zinc absorption known, and its effects are particularly significant in populations that eat little or no meat. Traditional food preparation methods — such as soaking, fermenting, sprouting, and milling — can meaningfully reduce phytate levels and improve mineral absorption. These age-old techniques have practical, low-cost potential for improving nutrition. Phytate-to-mineral ratios in food can be used as a reliable tool to estimate how much iron and zinc the body will actually absorb, and these ratios should be factored into dietary guidelines rather than just looking at total mineral content. Current dietary requirements for iron and zinc may be underestimating how much people on plant-heavy diets actually need, because they don't always account for phytate's blocking effect. Better phytate composition data for foods is urgently needed to help researchers, policymakers, and nutrition programs accurately assess and address mineral deficiency risks — particularly for zinc, which is harder to measure and often overlooked.
Bottom line: This paper makes a compelling case that the nutritional quality of a plant-based diet cannot be judged by nutrient content alone — how much the body can actually absorb is equally important. Policymakers, dietitians, and global health programs need to factor in phytate when setting dietary recommendations and designing food assistance programs, especially for vulnerable populations in developing regions.
PMID: 30010865
DOI: 10.1093/nutrit/nuy028
Abstract
Plant-based diets in low-income countries (LICs) have a high content of phytic acid (myo-inositol hexaphosphate [InsP6]) and associated magnesium, potassium, and calcium salts. Together, InsP6 acid and its salts are termed "phytate" and are potent inhibitors of iron and zinc absorption. Traditional food processing can reduce the InsP6 content through loss of water-soluble phytate or through phytase hydrolysis to lower myo-inositol phosphate forms that no longer inhibit iron and zinc absorption. Hence, some processing practices can reduce the need for high-dose iron fortificants in plant-based diets and alleviate safety concerns. Dietary phytate-to-iron and phytate-to-zinc molar ratios are used to estimate iron and zinc bioavailability and to identify dietary iron and zinc requirements according to diet type. The European Food Safety Authority has set adult dietary zinc requirements for 4 levels of phytate intake, highlighting the urgent need for phytate food composition data. Such data will improve the ability to estimate the prevalence of inadequate zinc intakes in vulnerable groups in LICs, which will facilitate implementation of targeted policies to alleviate zinc deficiency.