Legumes store phosphorous as phytic acid. {Phosphorous allow plants to grow gloriously. Photosynthesis...}
When phytic acids bind to minerals in the plant they are called phytates. These phytates have an antri-nutrient effect
preventing iron, zinc, and calcium from being absorbed into the body. Soaking takes out some of the phytates.
Some say that this is only a problem if beans
are your only source of nutrition, such as third world countries.
Men and women lose approximately 1 mg of iron per day - beans or no beans.
Vegan eaters often consume more iron than omnivores. Yet, they also consume more anti-nutrients,
including phytates, and these reduce the amount of iron available to their bodies.
Consuming 5-10 mg of phytic acid can reduce iron absorption by 50%.
Vitamin D status in the body seems to influence how much phytate is actually retained.
(Everyone in Seattle takes Vitamin D.) The more vitamin D, the more phytate retained;
the less vitamin D, the less phytate retained. If you have developed iron-deficiency anemia, you'd want to soak the beans.
I did read research that suggests if you're popping almonds for a snack that you will not absorb iron, zinc and maganese for
that snack time.
It will not stop you from absorbing minerals at dinner.
Some research suggests that the phytic acid in whole grains and beans protects against cardiovascular disease, cancer, and diabetes.
But only 10 out of 20 researchers agree, so I'm going to soak.
The American Journal of Clinical Nutrition, Volume 85, Issue 4, April 2007, Pages 1062–1067, Chittari V Harinarayan
High prevalence of low dietary calcium, high phytate
consumption, and vitamin D deficiency in healthy south Indians
Is Phytic Acid a Health Concern?