Can Sweet Potato Water Have a Slimming Effect?

A weight loss secret could lie in the starchy water produced from cooking a sweet potato, according to a new study.

Led by the National Agriculture and Food Research Organization in Japan, the study found mice on a high fat diet had a significantly lower body weight after one month of being fed a sweet potato peptide. The peptide was produced during digestion.

“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,” said lead author Koji Ishiguro in a press release. “Finding alternative uses for the sweet potato proteins in wastewater could be good for the environment and industry, and also potentially for health.”

Motivated by trying to find a new way to use the wastewater, the researchers began to investigate the effect of the proteins found in the water digested by the mice. Three groups of mice were fed high fat diets – one group was given the sweet potato peptide at a high concentration, while another was given the peptide at a low concentration.

The researchers then weighed and measured the mice’s liver mass and fatty tissues after 28 days. They also measured levels of cholesterol, triglyceride, leptin — which controls hunger — and adiponectin, which regulates metabolic syndrome.

Mice that were given the sweet potato peptide had a significantly lower body weight, liver mass, lower cholesterol and triglycerides and higher levels of the hunger and lipid-controlling hormones. Ishiguro said the study’s results were unexpected.

“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,” Ishiguro said.

The sweet potato peptide hindered weight gain, visceral fat gain and relieved fatty liver symptoms. It’s expected that the peptide could be used as a functional food material for people with metabolic disorders, but the necessary level of the peptide required would require human studies, the report’s conclusion said.

More than 105 million metric tons of sweet potato are produced globally every year, according to the International Potato Center. Almost 15 percent of sweet potatoes are used to produce starch materials, processed foods and distilled spirits in Japan.

The starch residues discharged during starch production are mainly used in animal feed and compost, but large amounts of the wastewater are discarded and can cause serious environmental problems. The sweet potato has been linked to several different health benefits, from anti-diabetic effects to inhibiting an HIV protease, the study said.

The study’s authors emphasized that further research is needed, especially human trials to determine the sweet potato peptide’s reach. Ishiguro said the study’s discovery of a new use for the wastewater could help in the long run.

“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,” Ishiguro said.