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.

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 their 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 couldn’t 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 hydrolyzed (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 soybeans. 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 phytic acid 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 beneficial. Personally, I prefer to take a supplement with zinc 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.

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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

I recently got into a discussion with someone on an email list about whether roasting nuts causes them to be rancid and if makes them unhealthy. This is a case where I did not go through the research and do a lit review, but here are my comments:

“I agree that it seems like nuts should go rancid if they are roasted, but they also contain antioxidants and other molecules which might protect them. Even the ALA in flaxseeds is protected when baked, and the Canola Council says that the ALA even in canola oil is not damaged by cooking. There is probably some rancidity in cooking nuts, but I tend to think it’s very little. My sense with the clinical trials on nuts is that they would be roasted since raw nuts are not as easy to digest for many people, and my bet would be that researchers have taken that into account. But I could very well be wrong. In epidemiological studies, which have also shown favorable results for nuts, I think it’s a safe bet that most of them are roasted.”

I’m guessing some of my readers have followed this in the scientific literature and can quickly point out any studies that have indicated whether the nuts were cooked or raw…

The person I was corresponding with pointed out this article by Andrew Weil which I thought was worth passing on:

http://www.drweil.com/drw/u/QAA400930/Are-Roasted-Nuts-Unhealthy.html