© Chris

In a previous article,1 I suggested that nut consumption should be limited or moderated because of the high levels of omega-6 fat many of them contain. But there's another reason you shouldn't make nuts a staple of your diet.

One of the main principles of the Paleo diet is to avoid eating grains and legumes because of the food toxins they contain. One of those toxins, phytic acid (a.k.a. phytate), is emphasized as one of the greatest offenders.

But what is often not mentioned in books or websites about the Paleo diet is that nuts are often as high or even higher in phytic acid than grains. In fact, nuts decrease iron absorption even more than wheat bread.2 This is ironic because a lot of people on the Paleo diet - who go to great lengths to avoid food toxins - are chowing down nut like they're going out of style.

What is Phytic Acid and Why Should We Care?

Phytic acid is the storage form of phosphorus found in many plants, especially in the bran or hull of grains and in nuts and seeds. Although herbivores like cows and sheep can digest phytic acid, humans can't. This is bad news because phytic acid strongly inhibits mineral absorption in adults3 - especially iron and zinc. Studies suggest that we absorb approximately 20 percent more zinc and 60 percent more magnesium from our food when phytic acid is absent.4

Phytic acid interferes with enzymes we need to digest our food, including pepsin, which is needed for the breakdown of proteins in the stomach, and amylase, which is required for the breakdown of starch. Phytic acid also inhibits the enzyme trypsin, which is needed for protein digestion in the small intestine.

As most people following a Paleo diet will probably have heard by now, diets high in phytate cause mineral deficiencies. For example, rickets and osteoporosis are common in societies where cereal grains are a staple part of the diet.5

How Much Phytic Acid Should You Eat?

Before you go out and try to remove every last scrap of phytic acid from your diet, keep in mind that it's likely humans can tolerate a small to moderate amount of phytic acid - in the range of 100 mg to 400 mg per day. According to Ramiel Nagel in his article "Living With Phytic Acid",6 the average phytate intake in the U.S. and the U.K. ranges between 631 and 746 mg per day; the average in Finland is 370 mg; in Italy it is 219 mg; and in Sweden a mere 180 mg per day.

If you're on a Paleo diet you're already avoiding some of the higher sources of phytic acid: grains and legumes like soy. But if you're eating a lot of nuts and seeds - which a lot of Paleo folks do - you still might be exceeding the safe amount of phytic acid.

As you can see from the table below, 100 grams of almonds contains between 1,200 - 1,400 mg of phytic acid. 100g is about 3 ounces. That's equal to a large handful. A handful of hazelnuts, which is further down on the list, would still exceed the recommended daily intake - and that's assuming you're not eating any other foods with phytic acid, which is not likely. Even the Paleo-beloved coconut has almost 400 mg of phytic acid per 100 gram serving.

[Disappointing side note for chocolate lovers: Raw unfermented cocoa beans and normal cocoa powder are extremely high in phytic acid. Processed chocolate may also contain significant levels.]

FIGURE 2: PHYTIC ACID LEVELS1 - In milligrams per 100 grams of dry weight

Brazil nuts - 1719
Cocoa powder - 1684-1796
Oat flakes - 1174
Almond - 1138-1400
Walnut - 982
Peanut roasted - 952
Brown rice - 840-990
Peanut ungerminated - 821
Lentils - 779
Peanut germinated - 610
Hazelnuts - 648-1000
Wild rice flour - 634-752.5
Yam meal - 637
Refried beans - 622
Corn tortillas - 448
Coconut - 357
Corn - 367
Entire coconut meat - 270
White flour - 258
White flour tortillas - 123
Polished rice - 11.5-66
Strawberries - 12

Can you prepare nuts to make them safer to eat?

Unfortunately we don't have much information on how to reduce phytic acid in nuts. However, we know that most traditional cultures often go to great lengths prior to consuming them. According to Nagel:6
It is instructive to look at Native American preparation techniques for the hickory nut, which they used for oils. To extract the oil they parched the nuts until they cracked to pieces and then pounded them until they were as fine as coffee grounds. They were then put into boiling water and boiled for an hour or longer, until they cooked down to a kind of soup from which the oil was strained out through a cloth. The rest was thrown away. The oil could be used at once or poured into a vessel where it would keep a long time.50

By contrast, the Indians of California consumed acorn meal after a long period of soaking and rinsing, then pounding and cooking. Nuts and seeds in Central America were prepared by salt water soaking and dehydration in the sun, after which they were ground and cooked.
Modern evidence also suggests that at least some of the phytate can be broken down by soaking and roasting. The majority of this data indicates that soaking nuts for eighteen hours, dehydrating at very low temperatures (either in a food dehydrator or a low temperature oven), and then roasting or cooking the nuts would likely eliminate a large portion of the phytic acid.

Elanne and I have been preparing nuts like this for a few years, and I personally notice a huge difference in how I digest them. I used to have a heavy sensation in my stomach after eating nuts, but I don't get that at all when I eat them after they've been prepared this way.

Another important thing to be aware of is that phytic acid levels are much higher in foods grown using modern high-phosphate fertilizers than those grown in natural compost.

So How Many Nuts Should You Eat?

The answer to that question depends on several factors:
  • Your overall health and mineral status
  • Your total intake of phytic acid from other foods
  • Whether you are soaking, dehydrating and roasting them nuts before consuming them
One of the biggest problems I see is with people following the GAPS or Specific Carbohydrate Diets, which are gut-healing protocols for people with serious digestive issues. Most GAPS and SCD recipe books emphasize using nut flour to make pancakes and baked goods. This is presumably because many people who adopt these diets find it hard to live without grains, legumes and any starch.

Unfortunately, nut flours have not been soaked and prepared properly, so they're likely to be loaded with phytic acid. The same is true - I hate to say - for coconut flour, which is now all the rage in the Paleo/GAPS community. Soaking nut or coconut flour for 18 hours before using it can help, but it does change the texture significantly - which many find undesirable.

It's also best to avoid most commercial nut butters, which are made with unsoaked nuts. However, some health food stores do carry brands of "raw, sprouted" nut butters that would presumably be safer to eat.

In the context of a diet that is low in phytic acid overall, and high in micronutrients like iron and calcium, a handful of nuts that have been properly prepared each day should not be a problem for most people. However, for more vulnerable populations - like those suffering from tooth decay, bone loss or mineral deficiencies, pregnant women, children under 6 years of age, or those with digestive malabsorption issues or serious illnesses - it's best to consume as little phytic acid as possible.

  1. How much omega-3 is enough? That depends on omega-6.
  2. Inhibitory effect of nuts on iron absorption (PDF)
  3. Effects of dietary fiber and phytic acid on mineral availability.
  4. Reduction of the phytate content of bran by leavening in bread and its effect on zinc absorption in man.
  5. Phytic acid and nutritional rickets in immigrants.
  6. Living With Phytic Acid