Is Boiled Sweet Potato Water Good for Anything?

December 14, 2025 •

4 min read

In 2016, research published in the journal Heliyon highlighted a discovery by Japanese scientists that wastewater from processing sweet potatoes contained unique peptides with potential benefits for weight loss. This groundbreaking study suggests that the starchy liquid leftover from boiling sweet potatoes may hold more value than previously thought, prompting a deeper look into its uses beyond simply being discarded.

Quick Summary

The liquid left over from boiling sweet potatoes contains beneficial compounds like sweet potato peptide (SSP) and some leached nutrients. Research has explored its potential for weight management, and it can also be repurposed for culinary applications like thickening sauces and for gardening, provided no salt was added during cooking.

Key Points

Weight Management Potential: Animal studies have shown that sweet potato peptide (SSP) found in the cooking water can suppress appetite and help with lipid metabolism.
Natural Thickener: The starchy liquid from boiling sweet potatoes is an excellent natural thickener for sauces, soups, and gravies.
Nutrient Boost for Plants: Unsalted sweet potato water contains trace minerals and carbohydrates that can be used as a natural, mild fertilizer for houseplants and gardens.
Eco-Friendly Compost Aid: Adding the starchy water to a compost pile can accelerate the decomposition process by feeding beneficial microorganisms.
Versatile Culinary Ingredient: Use the liquid in place of plain water in baking, or when mashing potatoes, to add moisture, flavor, and extra nutrients.
Requires Clean Potatoes: To use sweet potato water safely, especially for consumption, always ensure the potatoes are thoroughly washed before boiling to remove any dirt or residue.

Unlocking the Potential of Leftover Sweet Potato Water

For many, the murky, starchy water left in the pot after boiling sweet potatoes is simply discarded without a second thought. However, a growing body of evidence, including promising animal studies, suggests this leftover liquid may possess some interesting properties. The humble sweet potato, a nutritional powerhouse in its own right, contains a host of vitamins, minerals, and antioxidants. While some nutrients remain in the tuber, others, particularly water-soluble ones, inevitably leach into the cooking liquid. By understanding the composition of this liquid, we can explore its potential for both human health and practical household uses.

The Science Behind the Starch: Sweet Potato Peptides (SSP)

One of the most compelling discoveries regarding boiled sweet potato water involves a unique protein called sweet potato peptide (SSP). A Japanese study on mice found that those fed a high-fat diet with added SSP experienced significantly lower body weight and liver mass compared to a control group. The researchers hypothesized that SSP suppresses appetite and helps control lipid metabolism, leading to these slimming effects. While human trials are still needed to confirm these results, the findings offer a fascinating glimpse into the potential of repurposing this industrial and culinary byproduct.

Culinary Applications: From Thickeners to Broth Boosters

Beyond its potential health benefits, sweet potato water is a surprisingly versatile ingredient in the kitchen. Its starchy consistency makes it an excellent natural thickener for various dishes. Instead of reaching for cornstarch or flour, you can use sweet potato water to achieve a desired thickness and add a subtle, earthy flavor.

Gravies and Sauces: Replace some of the liquid with sweet potato water to create a richer, thicker consistency for gravies or savory sauces. The subtle sweetness pairs well with many savory flavors.
Soups and Stews: Add the leftover water to your next soup or stew. It will add body and depth of flavor while also incorporating some of the nutrients that have leached out during boiling.
Baking: For baking recipes that call for water, consider substituting sweet potato water. It can add a hint of moisture and a slightly sweet flavor, especially in quick breads or biscuits.
Mashed Potatoes: When mashing sweet potatoes (or even regular potatoes), use some of the reserved boiling water instead of milk or cream. This can enhance the sweet potato flavor and ensure the final dish remains creamy.

Repurposing for the Garden

Sweet potato water, especially if unsalted, can also be beneficial for plants. It contains trace minerals and starches that can give your garden a natural boost. However, proper application is key to avoid unwanted side effects.

Natural Fertilizer: Use the cooled, unsalted water to fertilize your plants. The minerals and trace amounts of vitamins can nourish the soil. This works well for both houseplants and outdoor gardens.
Compost Booster: Add the liquid to your compost pile. The starchy carbohydrates will feed the microorganisms responsible for decomposition, helping to speed up the composting process.
Rooting Cuttings: Some gardeners use starchy water to encourage new root growth in plant cuttings, a technique also used with water from regular potatoes. The carbohydrates can provide a source of energy for the new roots.

A Note on Safety and Preparation

Before considering consumption or other uses, it's crucial to ensure the water is prepared safely. Always wash the sweet potatoes thoroughly before boiling to remove any dirt or pesticide residue. Furthermore, if you plan to use the water for plants, do not add any salt to the boiling water, as this can harm soil and plant health.

Sweet Potato Water vs. Regular Potato Water


Feature	Boiled Sweet Potato Water	Boiled Regular Potato Water
Starch Content	Contains a good amount of starch, providing a naturally thick consistency.	Also starchy, making it useful as a thickener.
Nutrients	May contain leached water-soluble vitamins (B and C) and minerals, along with unique peptides.	Can contain leached vitamins and minerals, though the profile is different.
Flavor Profile	Possesses a subtle, slightly sweet flavor that can complement both sweet and savory dishes.	Flavor is more neutral and earthy, making it a good fit for savory applications.
Primary Uses	Potential weight management aid (based on animal studies), culinary thickener, plant food.	Primarily used as a culinary thickener for gravies and sauces, or for plant food.
Unique Compounds	Contains Sweet Potato Peptide (SSP) which shows promise in appetite suppression and lipid control in mice.	Does not contain SSP, though may have its own unique compounds.

The Final Word on a Kitchen Byproduct

While the search for a definitive human health miracle in boiled sweet potato water is ongoing, the evidence is compelling enough to warrant a second look at this often-discarded liquid. From potentially supporting weight management and digestion to being a practical and eco-friendly addition to your kitchen and garden, there are many reasons to save and repurpose this starchy liquid. As always, for any health-related applications, particularly drinking the water, ensuring the potatoes are clean and free of additives like salt is a non-negotiable step. So, the next time you boil sweet potatoes, hold on to that water and give it a new purpose. It might just be good for a lot more than you think.

Frequently Asked Questions

Yes, you can safely drink boiled sweet potato water, provided the potatoes were thoroughly washed beforehand and no salt or other additives were used. It has a mild flavor and contains some leached nutrients.

Yes, while most nutrients remain in the sweet potato itself, some water-soluble vitamins and minerals do leach into the water during boiling. The water also contains unique proteins, such as sweet potato peptide (SSP), studied for its potential health effects.

Animal studies have shown that a peptide found in sweet potato wastewater, SSP, may help with appetite suppression and fat metabolism, but more research is needed to confirm these effects in humans.

You can use the starchy water as a natural thickener for sauces, gravies, and soups. It can also be added to mashed potatoes, used in baking, or as a flavorful liquid base for rice.

Unsalted, cooled sweet potato water can be a mild fertilizer for plants, providing trace minerals and starches that can aid growth. You can use it to water plants or add it to a compost pile.

Some water-soluble nutrients, like Vitamin C, can be lost during boiling. However, boiling can also make some nutrients, like beta-carotene, more bioavailable and can lower the glycemic index of the sweet potato.

Sweet potato peptide (SSP) is a protein found in the wastewater from boiling sweet potatoes that has shown promising effects in animal studies for controlling appetite and regulating lipid metabolism.