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While it may seem difficult to argue against the benefits of plant-based diets, there are some compounds in plant foods that have a bad reputation for being “anti-nutrients.” I’ve published an article on this subject and discussed two of them in previous blogs: lectins and oxalates. A third commonly considered anti-nutrient is phytate.

Does the science back up the current trend of some nutrition camps to malign phytates? Let’s see what it has to say. 

What Are Phytates? 

Phytate is a compound composed of phosphate and inositol found mostly in legumes, whole grains, and nuts. In many seeds and other plant foods, the phytate content makes up the bulk of the phosphorus content. Phytate also goes by the name of phytic acid and inositol hexaphosphate (IP6).

 Why Phytates May Cause a Problem

If phytate is a natural compound found in many historically nutritious staples such as nuts, seeds, grains, and beans, why has it suddenly become an issue? One of the main reasons why phytates fall under the category of anti-nutrient is because they limit mineral absorption, especially calcium, iron, and zinc due to binding to these essential minerals.

This chelation depends on the proportion of phytate to metal and the pH. The ideal ratio is a molar ratio of phytate to iron around 0.4, while those above 1 can limit the absorption of iron. For zinc, ratios higher than 15 impedes bioavailability, and those below 5 are best. The best molar ratio for phytate to calcium has been shown to be 0.17, with anything above that contributing to impaired absorption.

Phytate is the main dietary inhibitor of zinc availability. Because many developing countries rely on grains and legumes for staples in their diets, there has been concern about the risk of zinc deficiency or insufficiency in these populations. There is also concern that a predominantly vegetarian diet may also increase the risk of a zinc deficiency, as well as other minerals, due to an increase in phytate-rich foods in the diet.

Although many studies support the hypothesis that phytate impacts zinc bioavailability, one study on young children (8 to 50 months old) found phytates to have a minute and not statistically significant impact on zinc bioavailability and status in children. Increasing dietary phytate by 500 mg/day only led to less than a 0.04 mg per day reduction in zinc absorption. There was a difference in the absorption rate based on age, height, and weight.

Due to phytate’s impact on the zinc absorption, it is recommended that DRIs be increased to reflect the reduced bioavailability in most diets, and the same need to increase DRIs has been shown for iron.

Phytate’s impact on iron bioavailability may be more complex than that with zinc, however. In one study, even after removing more than 90% of IP6 in two types of sorghum flour blends using phytase treatment, the bioavailability of the iron was not improved. However, dietary fiber removal through hydrolysis was found to have a more positive effect on iron absorption, demonstrating an independent impact of fiber on iron bioavailability not connected with phytate.

Phytate may also impact protein digestion by interacting with the activity of digestive enzymes due to chelating the mineral cofactors or binding to the protein.

Although mineral bioavailability is one of the main concerns with phytates, one older animal study found that mineral absorption was greater in whole wheat flour compared to refined white flour.

Foe… or Friend? The Potential Antioxidant Capabilities of Phytate

Although many focus on the negative impact of phytic acid on mineral status, it also has some beneficial characteristics. It is a natural antioxidant, mainly acting to inhibit free radicals by preventing Fenton reaction, or oxidative reactions involving iron that produce potentially damaging free radicals and oxidative species.

Potential beneficial effects of IP6 (some of which are still in the animal study or mechanistic study stage) include:

• Blocking calcification
• Decreasing the formation of advanced glycation end products (AGEs)
• Reducing serum lipids
• Providing protective effects for neurodegenerative diseases
• Prevention of kidney stones
• Inhibition of cancer development
• Protection against fatty liver disease
• Protection against osteoporosis
• Prevention of age-related cardiovascular calcification
• Protection against cardiovascular calcification in those with chronic kidney disease

Additionally, an animal study found that phytate improved butyrate and other SCFA concentration in the gut and reduced proinflammatory cytokines in rats consuming a high-fat diet. Short-chain fatty acids, especially butyrate, provide numerous health benefits, including protection against colon cancer, anti-inflammatory properties, regulation of genes, modulating the immune system, and more.

Reducing Phytates

As with many of the other anti-nutrients such as lectins and oxalates, growing methods and conditions as well as processing and preparation—such as soaking, cooking, milling, germination, sprouting, and fermentation—can decrease the amount of phytate, allowing for the minerals bound to the phytate to be released and absorbed. However, soaking and dehulling may also impact the mineral bioavailability in the food. Some studies show that soaking may not be the best method to increase mineral availability in maize and sorghum. Sourdough bread also has reduced phytate content and higher magnesium bioavailability.

Vitamin C, a substance already known to aid in improving the bioavailability of iron from plant sources, has also been shown to help in increasing bioavailability of iron when it is combined with phytate, such as in bran, in a dose of at least 30 mg.

Fermentation has also been found to improve iron bioavailability, likely due to increasing ferric iron. In one study, the participants were fed a low- and high-phytate meal with fermented vegetables instead of fresh vegetables. The iron absorption increased from 13.6 to 23.6% in the low-phytate meal and 5.2 to 10.4 in the high-phytate meal, while the zinc absorption had a minimal change, with 42.3 to 46.1 in the low-phytate meal and 12.9 to 13.4 in the high-phytate meal.

Although this study only showed a change in iron absorption, fermentation also helps increase the bioavailability of the other minerals. In another study, fermentation significantly increased the levels of calcium, iron, and zinc in teff and wheat, and the molar ratios of phytate to the minerals were significantly lowered as well.

Adding complementary foods can also increase mineral absorption. One study found that adding in liver and egg yolk increased iron and zinc bioavailability in a meal with rice and maize, and small dried fish led to increased calcium absorption.

The microbiome may also help increase zinc absorption when phytate-rich foods are consumed. One study found an increase in zinc bioavailability when phytate was consumed along with resistant starch, likely due to a lowering of cecal pH values (a biomarker of colonic fermentation among others) allowing for an increase in the solubility of zinc. Certain bacteria may also produce phytase, which also helps break down phytate and release the minerals for absorption in the colon, although research in humans is limited.

People may also adapt to high-phytate diets, leading to a reduced impact on the bioavailability of the minerals. In one small study, regular consumption of a high-phytate diet for 8 weeks led to an increase in serum iron response post-meal, with a 41% increase in those with suboptimal stores of iron. The study did not look into possible mechanisms for this adaptation. Another study found that consuming a diet rich in phytate led to an increase in bacteria species in the microbiota able to degrade phytate. Conversely, an older study found no intestinal adaptation to a high-phytate diet.

So, what does all this mean for you and your diet? Phytate does bind with minerals, especially calcium, iron, and zinc. But does that mean you need to reduce them from your diet? That depends on the specifics of your situation, but for most people, consuming phytate-rich foods as part of a diverse diet should not impact their overall mineral status, especially consuming foods traditionally processed, such as with soaking or fermentation. As a bonus, you can benefit from some of the benefits of the antioxidant and other protective effects of phytate.

Some people may be more at risk of mineral deficiencies or sensitive to phytates, leading to a need to limit them in the diet. Talk to your doctor, nutritionist, or another health practitioner about your concerns and situation to determine whether limiting phytate-rich foods in your diet makes sense for you.