Part 1: Soaking – Nuts

This is Part 1 of a two part series. In Part 2, I will discuss research on whether soaking beans reduces their propensity to produce intestinal gas. I apologize in advance to those who do not care to discuss such things.

Question:

I’m a mom of three vegan kids (13, 8, and 5) so I’m always tweaking our diet to ensure we are eating well. The kids eat a variety of nuts (usually on a daily basis) and I was wondering if we should be soaking them first to aid in digestion and absorption of nutrients. I know raw foodists suggest soaking, but I’ve never seen anything about this from a reputable source.

Answer:

It’s not easy to find much information on soaking nuts, but here is what I came up with…

Phytic acid is a molecule found in many seeds of plants. Legumes and grains tend to have large amounts of phytic acid, which often attach to calcium, magnesium, iron, or zinc and prevents it absorption.

I see many articles claiming that nuts are also high in phytic acid, but I could not confirm this to my satisfaction and so it should come as no surprise that I could not find any research on whether soaking nuts could reduce their phytic acid content.

I did find two papers discussing the research on soaking legumes and grains:

The first review said that ten hours of incubating California small white beans at 140°F (60°C) resulted in an almost complete loss of phytic acid, with 75% being hydrolysed (broken into phosphorus and inositol) and 25% being diffused into the water. Germination reduced phytic acid by over 60% in garbanzo beans and over 40% in soy beans. Boiling reduced phytic acid in soybeans by 40%. Soaking for 12 hours in room temperature water reduced phytic acid by 7.7, 8.1, 13.2, and 19.1%, respectively, for black-eyed beans, red kidney beans, mung beans, and pink beans. Soaking for 18 hours reduced it by 52.7, 69.6, and 51.7% in pinto, Great Northern, and red kidney beans. So, as far as legumes go, soaking for 18 hours appears to be fairly effective at reducing phytic acid levels (1).

Another review (2) showed that soaking maize for 24 hours reduced phytic acid by about 50%, with most of the reduction occurring in the first hour. It said that soaking also removes other anti-nutrient factors such as saponins, trypsin inhibitors, and polyphenols.

Given the above, I would say that if nuts are high in phytic acid, soaking is likely to reduce it. And because vegans’ zinc intakes tend to be marginal, increasing the zinc absorption from nuts would be great. Personally, I prefer to just take a supplement with zinc to make sure I get enough rather than worrying if I’m absorbing enough from the food I eat.

One final note about soaking nuts:

In the comments section of the article, Go nuts for better health,” in The Sydney Morning Herald (July 13, 2012), Lisa Yates, Program Manager and Dietitian of the organization Nuts for Life (established by the Australian nut industry), points out that the many studies showing nuts to reduce the risk of heart disease and type-2 diabetes use unsoaked nuts, so, there is no reason to think that you must soak them to receive the benefits.

You can support JackNorrisRd.com by purchasing anything through these links

1. Urbano G, López-Jurado M, Aranda P, Vidal-Valverde C, Tenorio E, Porres J. The role of phytic acid in legumes: antinutrient or beneficial function? J Physiol Biochem. 2000 Sep;56(3):283-94. | link

2. Mensah P, Tomkins A. Household-level technologies to improve the availability and preparation of adequate and safe complementary foods. Food Nutr Bull. 2003 Mar;24(1):104-25. | link

7 Responses to “Part 1: Soaking – Nuts”

  1. Mattheworbit Says:

    Hi Jack,

    I realise this is probably a silly question, but I wanted to check:

    In most cases, we soak beans/legumes before we cook them, generally for at least 6-12 hours. Is this the soaking referred to in the study as having benefits? And if so, wouldn’t all beans be soaked (other than those pressure cooked, which presumably would also reduce the phytic acid amongst other things?)

    If not, what types of prepared beans are we talking about here (i.e. unsoaked?)

  2. Jack Norris RD Says:

    Mattheworbit,

    Yes, they are talking about beans soaked versus unsoaked, and they were tested for phytic acid levels without first cooking.

  3. rick Says:

    It has been a while since I looked into this, but as I recall, nuts and legumes have growth inhibitors which help prevent germination/sprouting. Soaking deactivates the growth inhibitors. That makes sense; the plants have a mechanism that tells them when to remain in stasis, and when conditions are suitable to grow.

    I further understand that growth inhibitors cause digestive problems. I do not recall whether they also inhibit absorption of nutrients. I do not know whether growth inhibitors and phytic acid are the same or different things. Moreover, I understand that cooking similarly deactivates the growth inhibitors.

    Last, I understand that sprouting grains dramatically boosts their nutrient content. I do not know whether the properties that I discuss above are similarly applicable to grains, but if not, I wonder why.

    It would be great if you could please shed some light on these aspects. Perhaps you had already planned to do so for part II.

  4. Betty A. Says:

    And then the soaking water should be discarded, and fresh water used for cooking?

  5. Jack Norris RD Says:

    Rick,

    You are probably talking about trypsin inhibitors. That will be for Part 3.

    Phytic acid is not the same thing as growth inhibitors, to my knowledge, though phytic acid is involved in the plant germinating.

    > Last, I understand that sprouting grains dramatically boosts their nutrient content.

    It would definitely release some of the nutrients that are bound to phytic acid for absorption. Whether it creates any new vitamins (per serving) I’m not sure. I can try to look into that for a future post.

  6. Jack Norris RD Says:

    Betty,

    > And then the soaking water should be discarded, and fresh water used for cooking?

    Yes.

  7. MichaelG Says:

    The “mom of 3 vegan kids” asked if soaking nuts can “aid in digestion and absorption of nutrients”, and Jack’s article focuses on potential reduction of phytic acid. But I’m far from convinced that phytic acid is a problem. In theory it reduces mineral absorption but is there any (epidemiologic) data indicating disease or mortality among people with balanced diets that happen to be high in phytic acid? I doubt it. Reference 1. abstract mentions “Enzymes capable of hydrolysing phytates are widely distributed in micro-organisms, plants and animals.” Some reports indicate the natural gut “probiotic”, bifidobacterium pseudocatenulatum, breaks down phytic acid – try googling some of the phrases I’m using here. And if it’s not completely broken down, so what? Phytic acid is an antioxidant with nutritional benefits, including anticarcinogenic properties, reduced risk of kidney stones, and you can also try googling “Phytic acid as a potential treatment for alzheimer’s”. I’m not criticizing sprouting, soaking, and so on – I soak legumes for, uhm, aesthetic reasons. What I am concerned about is vegans accepting unsubstantiated anti-phytate propaganda that is coming from some nonvegans. There’s plenty of research about phytic acid’s nutritional advantages.

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