Phytic acid is an antinutrient found in all plant foods, especially grains, legumes, and nuts. It earned its “antinutrient” moniker by virtue of the fact that it chelates, or binds to, minerals like zinc, iron, magnesium, calcium, chromium, and manganese in the gastrointestinal tract. People who eat a diet high in phytic acid put themselves at risk of serious mineral deficiencies like anemia1 and rickets.23
As Primal eaters, we already eschew beige blah grain-based foods. Legumes occupy a middle ground. Even though a lot of ancestrally aligned folks avoid them, I put them in the “okay in moderation” category for people who want to eat them and who don’t seem to suffer ill effects, GI-wise. I don’t think they should be a dietary centerpiece, but they aren’t as bad as some folks make them out to be.
As for nuts, these are tricky in the ancestral and low-carb spaces. On the one hand, they’re crunchy, fatty, nutritious, and convenient. They travel well. Nut flours make pretty decent substitutes for grain flours in baked goods if that’s your cup of tea. My love of macadamias is well-documented. On the other hand, they are energy dense (which can be a good or bad thing depending on the context) and fairly high in omega-6 fatty acids. While I’m not as concerned about omega-6s in nuts as I once was—the omega-6 load from industrial seed oils is a far bigger worry—I know that many in the ancestral community still carefully watch their omega-6 intake.
Then there are the antinutrient concerns we’re going to talk about today. I’ve seen how some folks go absolutely nuts for nuts in the low-carb and keto spaces, eating great handfuls at a time and using bag upon bag of almond flour. And it’s not just ancestral eaters who embrace nuts. Nuts are the common bond between all dietary creeds. Vegans use them for the protein. They’re a staple of the Mediterranean diet. Everybody loves almond butter.
There’s no doubt they’re ubiquitous and that they have a solid reputation as a health food. But what about the phytic acid content? Are we all turning a blind eye to significant antinutrient concerns because nuts are just so darn tasty, or are those who raise alarms about phytic acid making a mountain out of a molehill? Let’s explore.
What is Phytic Acid?
Phytic acid, aka IP6, is how plants store phosphorous. When phytic acid is bound to a mineral like calcium, that’s phytate. As I said, phytic acid binds to minerals in the food you eat, making it so your body can’t use them as intended. Animals that produce phytase—the enzyme that breaks down phytate—can thrive on phytate-rich foods. Rats, for example, produce ample amounts of phytase and can handle more dietary phytate without exhibiting signs of mineral deficiencies. Since humans produce around 30 times less phytase than rats, phytate-heavy diets might be problematic for humans.
While too much phytic acid in the diet is problematic, you wouldn’t want to completely eliminate phytate from your diet, even if it were possible. A number of health effects are associated with moderate intake of phytic acid, like:
Phytic acid can inhibit calcium crystallzation and reduce kidney stone development.4
If you have hemachromatosis (a tendency to absorb too much iron), you actually want to reduce your iron absorption, and dietary phytic acid can (famously) do just that.5 It’s also one of the only iron chelators that does not induce lipid peroxidation or the formation of reactive oxygen species.6
Phytate may also be an effective anti-cancer agent with the curious tendency to ignore the healthy cells and focus only on the cancerous ones.7
As with so many things in nutrition, “the poison is in the dose.”
What Foods Are Highest in Phytic Acid?
By dry weight, nuts generally contain more phytic acid than similar amounts of grains and legumes. Here are the estimated phytic acid contents of common foods according to a 2009 analysis.8
These values are milligrams per 100 grams of dry weight:
As you can see, nuts top the list. The range of values is due to different papers reporting different phytic acid levels in these foods, but if this is accurate, almonds could have upwards of nine times the amount of phytic acid per 100 grams as rice. Of course, 100 grams of rice is only about half a cup. It’s pretty easy to eat four times that our more with a standard meal of stir fry or a burrito bowl. A hundred grams of nuts is somewhere between three-quarters and one cup of nuts, give or take. That’s a pretty hefty serving—definitely more than the “palmful” serving most people recommend.
Nut milks also contain phytic acid, but I wasn’t able to find any definitive answers as to how much. The nuts used to make nut milks are often soaked, sprouted, and heated, and phytase enzymes may be added to the final product, all of which would reduce phytic acid activity.9
Best Practices for Including Nuts in Your Diet
Phytic acid or no, nuts contain modest amounts of protein plus monounsaturated fats and micronutrients we want and need. There’s no need to exclude them from your diet. Do watch your intake, though. Although asking “What would Grok do?” doesn’t give us definitive prescriptions for what we ought to do, it can be a helpful starting point. How would our ancestors have eaten nuts? By the pre-shelled and salted bagful? Or by the laboriously gathered and hand-shelled occasional handful? Eating nuts is effortless now, but it wasn’t always like that. Ever crack a macadamia shell by hand? A Brazil nut? An almond? It’s hard work. You’re either trying to break open a rock-hard shell or sifting through fragments of shell and nut to find something edible. If you eat your nuts like you had to gather and shell them yourself—rather than gorging on them by the handful—you won’t be able to consume a significant amount of phytic acid.
If you’re still worried about phytic acid from nuts, soaking and sprouting eliminates much of the phytic acid activity. Taking some vitamin C with the phytic acid will further inhibit its iron-binding ability.
You can also play around with food timing. In order for phytic acid to impair absorption, it has to physically come into contact with the minerals in question. Mineral absorption—or non-absorption caused by phytate chelation—happens in the gastrointestinal tract, that wild and crazy place where masticated and partially digested food particles gather, mingle, and sometimes pair up. Thus, keeping the food in your gut away from the phytic acid in your gut by eating the nuts separate from other foods might improve your mineral status. Alternately, eat nuts alongside animal protein. There’s some evidence that phytic acid doesn’t inhibit iron absorption as much when consumed with pork, fish, or beef organs.10 (Other types of meats probably work the same way; these are just the ones that have been studied.)
Finally, rest easier knowing that if you regularly consume nuts (or legumes for that matter), your gut adapts to better handle the phytate load, perhaps due to an increase in the necessary microbes and/or greater phytase activity.1112
Unless you’re a Hadza, you shouldn’t be relying on nuts for the bulk of your nutrients and calories. And that’s the important thing: you don’t have to, nor are you compelled to, because the Primal eating plan is an overall nutritious one, full of mineral-rich vegetation, animals, and yes, the occasional handful of nuts. You’re not relying on plant foods for your zinc. You’re eating shellfish and beef and lamb for the far-more-bioavailable animal-based zinc.
According to the evidence I was able to find, phytic acid simply isn’t a major concern in the context of a nutritious diet, especially one that contains ample amounts of animal-based minerals and protein. Go ahead and eat and enjoy nuts in moderation, an ounce or two (especially soaked) as long as you’re eating an otherwise nutrient-dense diet.
Thanks for reading, everyone. Be sure to leave your thoughts in the comment section.
Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.