Walnut-soaked water (WSW) is the liquid remaining after raw walnuts have been steeped, typically overnight, before consumption. This practice, often done to improve the nut’s texture and palatability, has led to numerous claims about the health properties of the water itself. This analysis determines if drinking WSW offers any tangible health advantage, shifting focus from the well-established benefits of the walnut to the contents of the soaking liquid.
Why People Soak Walnuts
The primary motivation behind soaking walnuts is to enhance the nut’s digestibility and perceived nutritional value. Walnuts contain natural compounds known as enzyme inhibitors and phytic acid, sometimes called anti-nutrients. These compounds can impede the full absorption of minerals like zinc and iron. By soaking the walnuts, proponents aim to neutralize these inhibitors, thereby increasing the bioavailability of its beneficial components.
Beyond digestion, the practice is also used to reduce the natural bitterness associated with the outer skin of the walnut. This bitterness is caused by water-soluble tannins, which leach into the liquid during the soaking process. Anecdotal and folk health claims also drive the practice, with some users believing the water supports thyroid function, aids in weight management, or promotes better sleep and relaxation.
What the Water Contains
The soaking process is a form of aqueous extraction, where water-soluble compounds migrate from the nut kernel and its skin into the surrounding liquid. The most significant compounds transferred are phytic acid, enzyme inhibitors, and tannins. Tannins are responsible for the dark, brownish color and astringent, bitter flavor of the used water.
Phytic acid is also partially dissolved, which is the main goal of soaking the nuts to improve mineral absorption. The water also absorbs trace amounts of water-soluble micronutrients, such as certain B vitamins and minerals, though the concentration is typically low. The vast majority of the walnut’s most valuable nutritional components—including its healthy omega-3 fatty acids, fiber, protein, and fat-soluble vitamins—remain locked within the structure of the nut itself.
Assessing the Health Benefits
Scientific analysis of the claims surrounding walnut-soaked water must be tempered by the reality of its chemical composition. The water contains the very compounds—phytic acid and tannins—that are considered anti-nutrients or compounds that cause a bitter taste. While the water does contain trace minerals and vitamins, the concentrations are negligible compared to the amounts found in the whole walnut. Therefore, any purported health benefit from drinking the water is highly unlikely to be due to a significant nutrient dose.
The popular claims of thyroid support or metabolic boost are not supported by evidence that the leached compounds are present in therapeutic concentrations. The primary benefit of soaking is the improved digestibility of the nut due to the removal of phytic acid and enzyme inhibitors, not a unique benefit in the liquid. Consuming the whole, soaked walnut provides the full profile of healthy fats, protein, and fiber that are responsible for the nut’s established benefits on heart and brain health.
Safe Preparation and Potential Risks
The preparation of walnut-soaked water carries specific safety considerations, particularly concerning microbial contamination. Soaking walnuts in water, especially for extended periods at room temperature, creates a moist environment that can promote the growth of foodborne pathogens, such as Salmonella and E. coli. Studies have shown that bacterial populations can significantly increase within 12 to 24 hours when the water temperature is around 22°C.
To mitigate this risk, it is strongly recommended to use clean, filtered water and to soak the nuts in the refrigerator if the process exceeds eight hours. The general recommendation for maximizing safety and removing the undesirable compounds is to discard the soaking water entirely and thoroughly rinse the walnuts before consumption. Beyond the microbiological risk, the water’s high concentration of leached tannins can cause minor digestive upset in sensitive individuals and has a distinctly bitter taste.