Sweet potatoes are creamy and sweet enough to be made into delicious holiday pies, but they are also surprisingly healthy and nutritious. In addition to this, new research suggests that even the cooking water from sweet potatoes may help with digestion and weight loss.
Sweet potatoes are an exceptionally nutritious vegetable. High in carotenoids, sweet potatoes are a great source of vitamin A, which is great for eye health, has antioxidant and anti-aging properties, and has also been linked to cancer prevention.
Additionally, sweet potatoes are rich in a wide range of B vitamins, including B-1, or thiamine, B-2 and B-3 - riboflavin and niacin, respectively - as well as B-5 and B-6. According to the National Institutes of Health, B vitamins help our body process food into energy, as well as form red blood cells.
New research - published in the journal Heliyon - suggests the starchy water left over from cooking sweet potatoes may have slimming effects and help digestion.
A team of researchers - led by Dr. Koji Ishiguro from the National Agriculture and Food Research Organization in Japan - were looking for ways to reuse the wastewater resulting from processing sweet potatoes on an industrial scale. As such, they thought of testing its nutritional value and dietary effects.
Environmental impact of sweet potato industrial use
According to the International Potato Center, sweet potatoes are one of the world's most important food crops, with 105 million metric tons of the vegetable being produced every year around the world, and 95 percent of the crops being grown in developing countries.
Sweet potatoes are very suitable for processing due to their high starch content. Sweet potato is currently used to produce flour, noodles, bread, candy, pectin, liquors, and other starch and starch-based industrial products.
In Japan, around 15 percent of sweet potato is used to produce starch-derived products, as well as processed foods and distilled spirits.
The result is a large amount of wastewater that contains organic residue and is usually discarded in rivers and oceans. This could cause serious environmental problems.
Since the wastewater also contains proteins, Dr. Ishiguro and team decided to investigate its effects on digestion in mice.
"We throw out huge volumes of wastewater that contains sweet potato proteins - we hypothesized that these could affect body weight, fat tissue, and other factors. Finding alternative uses for the sweet potato proteins in wastewater could be good for the environment and industry, and also potentially for health."
Dr. Koji Ishiguro
Protein found in sweet potato water has slimming effects in mice
Researchers fed three groups of mice high-fat diets. One of the groups was given the sweet potato peptide protein (SPP) in a high concentration, and another group in a low concentration.
After 28 days, researchers weighed the mice and took a series of measurements. They examined their liver mass and measured their fatty tissue, fat cholesterol levels, and triglyceride levels. Scientists also measured the levels of leptin and adiponectin, which regulate the body's metabolism and play a key role in obesity and metabolic syndrome.
Mice that were fed higher levels of SPP had significantly lower body weight and liver mass.
These mice also had lower cholesterol levels and triglycerides, as well as higher levels of the metabolic hormones leptin and adiponectin.
The findings suggest that SPP suppresses the appetite and controls lipid metabolism in mice.
Further research is needed to see if the same effects apply to humans, but Dr. Ishiguro says the results are "very promising."
"We were surprised that SPP reduced the levels of fat molecules in the mice and that it appears to be involved controlling appetite suppression molecules. These results are very promising, providing new options for using this wastewater instead of discarding it. We hope SPP is used for the functional food material in future."
Dr. Koji Ishiguro