Soaking beans does remove some nutrients, but the losses are relatively small and largely offset by an important benefit: soaking also removes compounds that block your body from absorbing minerals in the first place. The net result is that soaked beans often deliver more usable nutrition than unsoaked beans, even though their total nutrient content on paper is slightly lower.
What Actually Leaches Out During Soaking
When dry beans sit in water for 8 to 12 hours, water-soluble vitamins and minerals gradually migrate into the soaking liquid. The extent varies by bean type and soaking conditions, but the numbers are generally modest for vitamins. Faba beans soaked for 9 hours lost up to 15% of their thiamine (vitamin B1) and up to 11% of their riboflavin (B2), with no measurable niacin loss. Chickpeas fared slightly worse, losing up to 18% of thiamine and as much as 46% of available niacin. Lentils showed an interesting quirk: while they lost 5 to 10% of thiamine and 26 to 42% of niacin, their riboflavin content actually increased by up to 98%, likely due to microbial activity during the soak. Soaking in alkaline solutions (like water with baking soda) tends to increase vitamin losses across the board.
Mineral losses can be more noticeable. Iron content dropped 28 to 40% in faba beans after soaking, and zinc losses reached up to 30%. These numbers sound alarming on their own, but they only tell half the story.
Why Raw Numbers Don’t Tell the Whole Story
Dry beans contain high levels of phytic acid, a compound that binds tightly to iron, zinc, calcium, magnesium, and manganese, making them largely unavailable for absorption. You could eat a bowl of unsoaked, cooked beans with plenty of iron on the nutrition label, yet your body might absorb only a fraction of it because the phytic acid is holding onto those minerals.
Soaking is one of the most effective ways to break down phytic acid. In chickpeas, soaking for 2 to 12 hours reduced phytic acid content by 47 to 56%. That reduction frees up minerals that were previously locked away. A study published in Scientific Reports found that soaking common beans in plain water improved the bioaccessibility of iron, zinc, and copper compared to untreated beans. Iron bioaccessibility increased notably, and zinc bioaccessibility rose from about 5.5% to nearly 6.7%. Those may sound like small percentages, but in practical terms, your body is extracting more usable mineral from each serving.
So while the total mineral content of soaked beans is lower than raw beans, the minerals that remain are easier for your gut to absorb. The trade-off generally works in your favor.
Protein Stays Mostly Intact
Protein is the nutrient most people associate with beans, and soaking has minimal impact on it. Total protein content stays largely stable through soaking alone. Some losses in specific essential amino acids have been observed, but they’re small. Fermentation is the only common preparation method shown to meaningfully improve protein nutritive value (by about 8%), so if you’re focused on maximizing protein, soaking won’t hurt you, but it won’t help much either.
Less Gas, Better Digestion
Beans contain sugars called alpha-galacto-oligosaccharides, which your small intestine can’t break down. They pass intact to your large intestine, where gut bacteria ferment them and produce gas. Soaking reduces these sugars by 10 to 40%, depending on the legume. Chickpeas saw the biggest drop at around 40%, while lentils and faba beans lost closer to 10%. This won’t eliminate digestive discomfort entirely, but it takes the edge off for most people.
Soaking also reduces other compounds classified as antinutrients, including certain phenolic compounds. While these have antioxidant properties, high concentrations can impair digestion and reduce protein absorption. A partial reduction during soaking is considered beneficial rather than harmful.
Should You Keep or Discard the Soak Water?
This is the practical question most people are really asking. The soak water contains a mix of leached minerals, dissolved vitamins, phytic acid, gas-producing sugars, and other antinutrients. Drinking or cooking with that water would recapture some lost nutrients, but it would also reintroduce the very compounds you were trying to remove.
For most people, discarding the soak water and cooking with fresh water is the better choice. The nutrient losses are modest, and you gain meaningful reductions in compounds that cause digestive discomfort and block mineral absorption. If you’re soaking with baking soda to speed up cooking time, discarding the water is especially important since alkaline soaking increases both nutrient leaching and antinutrient removal.
You can further minimize losses by keeping your soak time reasonable. A standard overnight soak of 8 to 12 hours is enough to get the digestibility benefits without excessive leaching. Longer soaks at warm temperatures don’t add much benefit and can start to degrade bean quality.
The Bottom Line on Nutrition
Soaking beans creates a small nutrient trade-off that works in your favor. You lose a portion of water-soluble vitamins (roughly 5 to 18% of B vitamins in most cases) and some minerals from the total content. But you also strip away 47 to 56% of the phytic acid that was preventing your body from using those minerals efficiently, reduce gas-producing sugars by up to 40%, and improve the overall digestibility of the meal. The beans that reach your plate after soaking deliver more accessible nutrition per serving than the raw numbers suggest.