Many raw food proponents and certain healthcare traditions (such as Ayurveda) recommend that raw nuts be soaked for many hours, or overnight, as a way to help increase their digestibility. I've even seen statements about the effect of this soaking process on the nuts. These statements suggest that soaking deactivates enzyme inhibitors in the nuts. However, to my knowledge, there is no scientific research to substantiate the greater digestibility of soaked nuts.
There may be others advantages that come from soaking, but I have yet to see these advantages substantiated in any peer-reviewed, published research. It would make sense to me that some components in nuts would be partially broken down during the process of soaking. However, since nuts are approximately 75-80% fat in terms of their calorie content, the majority of nutrients in nuts would be fat-soluble rather than water-soluble and less subject to breakdown for this reason.
Finally, unlike dried beans, which require soaking in order to be digestible, raw nuts can definitely be eaten raw and digested normally if chewed well, eaten in moderation, and received by a healthy digestive tract. As is the case with all foods, I'd be in favor of certified organic nuts in order to avoid exposure to unnecessary toxic residues and to optimize the nutrient content.
It's important to note that one study has shown an increased risk from soaking of Brazil nuts, and that risk involves increased presence of coliform bacteria. Although it's impossible to make a generalization from this study, it's important to at least be aware that there may be possible downsides to the process of soaking.
If you do want to soak your nuts, I'd suggest doing so in a bowl of distilled/purified water for about five to eight hours or even overnight, which may be more convenient. Be sure to remove and discard the nuts that float to the top, as they are likely to have some rancidity. Drain and rinse well.
While I don't regularly soak nuts, I do so whenever I am going to make nut milk. I find that it is much easier to blend them in water after they have been soaked since they soften and you are more likely to get a milkier consistency.
For more information on this topic, see:
Arrus, K, Blank, et al. Microbiological and Aflatoxin Evaluation of Brazil NuPods and the Effects of Unit Processing Operations. J Food Prot. 2005;68(5): 1060-5.
Awang, M N. Fate of Betel Nut Chemical Constituents Following Nut Treatment Prior to Chewing and Its Relation to Oral Precancerous & Cancerous Lesion. Dent J Malays. 1998;10(1): 33-7.
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