I think there might have to be a Part 3 (and, who knows, maybe a Part 4, 5, and 6) to deal with all the questions regarding soaking foods. I might not do them in consecutive posts.
The flatulence caused by eating beans is normally attributed to the oligosaccharide content of the beans. Oligosaccharides are chains of sugar molecules, usually two to ten in length, and comprising of at least some sugars other than glucose. (Long chains of glucose-only molecules are considered starches and are typically easy to digest.)
The flatulence is caused by the fact that humans do not have digestive enzymes to break down the oligosaccharides and, instead, they are broken down by bacteria in the lower intestines which produce gas in the process.
Soaking reduces the amount of oligosaccharides in beans. But how does it compare to simply cooking? Unfortunately, in the time I had to search, I did not find a study that compared soaking and cooking to only cooking. But I did find a study that compared the oligosaccharide reduction in pinto beans among different preparation methods (1):
- Soaking for 18 hours: 10% reduction
- Soaking for 18 hours, then boiling for 90 minutes: 50% reduction
- Soaking for 18 hours, then autoclaving for 30 minutes: 57% reduction
Autoclaving is approximately the same as pressure-cooking.
It’s not clear from this study that you first need to soak the pinto beans to produce the 50% reduction in oligosaccharides.
In her article on reducing flatulence in veg diets, Dina Aronson, MS, RD suggests, “If you make beans from scratch, soak them overnight first, rinse them well, and rinse them several times during the cooking process, as this will help get rid of more of the gas-causing oligosaccharides. Also, the longer you cook beans (with rinsing), the better.”
It should also be noted that in their comments, the authors of the study above say, “Soaking of Great Northern, kidney, and pinto beans and their subsequent boiling for 90 min decreased the amount of [the oligosaccharides] raffinose and stachyose by 70-80%. In marked contrast, sucrose, raffinose, stachyose, and verbascose contents increased [emphasis added] following the cooking of red, Bengal, black, and green grams (1).”
Sigh. Luckily, I don’t think too many of us eat “grams,” so we probably don’t need to worry about that. I looked up the study and they did not soak the beans before cooking, so perhaps that was the problem (2).
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.
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.
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.
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