Does Soaking Beans Affect Nutritional Value?


You probably know that you should soak dry beans before cooking them. The main reason for doing this is to reduce the amount of time it takes to cook the beans. However, there are also other implications of soaking beans.

Oligosaccharides and Soaked Beans

The reason that beans give you gas is because they contain a type of starch called oligosaccharides. This starch plays an important role in digestion. It serves as food for bacteria that live in the digestive tract of animals. These bacteria help with digestion. However, carbon dioxide is formed as a byproduct of bacteria breaking down oligosaccharides, which is why beans give us gas.

When you soak beans, some of the oligosaccharides are leached into the water. If you throw this water away before cooking them, the beans won’t cause as much gas.

Nutrients Lost from Soaking Beans

Oligosaccharides aren’t the only nutrient which leaches out of beans when you soak them. Water-soluble vitamins, such as riboflavin, thiamin, and folic acid (which are all very high in beans) all are lost.

Numerous studies have been done to determine just how much nutrients are lost from soaking beans. All of the studies (at least the many that I read) showed that water-soluble vitamins were lost. Some non-soluble nutrients were also lost, such as Calcium, and Magnesium. However, the amount of nutrients lost was not significant enough to cause worry in anyone eating beans for their nutritional value.

A study published in Plant Foods for Human Nutrition found these differences in nutrients of beans:

Nutrient Cooked Soaked-Cooked
Protein 20.80 20.18
Fat 1.50 1.17
Ash 2.70 2.45
Carbohydrates 66.13 66.49
Crude Fiber 3.91 4.13
Soluble Fiber 5.11 6.41
Potassium 1035 831.25
Calcium 107.50 110.83
Magnesium 165.00 145.00
Iron 6.60 5.80
Copper 1.00 1.01
Zinc 2.93 2.76
Manganese 1.60 1.60
Thiamin 0.15 0.64
Riboflavin 0.38 0.34
Niacin 1.06 0.81

Interestingly, soaking before cooking actually increased the nutritional content of a select few nutrients, such as thiamin and calcium. This may be due to increased bioavailability from the beans being easier to digest after soaking.

Use Cold Water to Save More Nutrients

The temperature of the soaking water does have an effect on the nutrient loss from soaking. One study in the Journal of Food Science found that, “Losses of total solids, N compounds, total sugars, oligosaccharides, Ca, Mg, and three water-soluble vitamins (thiamin, riboflavin and niacin) were measured and found to be very small at soaking temperatures up to 50°C. An increase in those losses of from three- to fourfold was found when the soaking temperature was raised to 60° C or above.”

Should You Soak Beans or Not?

If you are really worried about getting the most nutrition possible from beans, then you should not soak them before cooking. However, this means you will have to cook the beans longer (which will reduce some of the protein content). It also means that you will end up with more gas.

Since the amount of nutrients lost from soaking beans isn’t really that great, I’d recommend soaking beans in cold water for about 12-24 hours before cooking them.


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Diane Vukovic

Diane Vukovic is a vegan mom, health nut, and kitchen diva. When she's not deducing veggie nutritional facts, she's probably dancing crazily with her daughter or traveling somewhere in Europe.