It sounds distinctly unappetising – but drinking the cooking water from sweet potatoes could help you to shed the pounds.
Quaffing the starchy liquid has been found to significantly lower body weight after just a month, scientists have found.
Not only that, drinking the water can also cut cholesterol by more than 7 per cent.
The liquid contains a key protein left over from cooking the vegetable, which may play a role in digesting fat.
The suggestion that sweet potato waste water could be a slimming aid comes from the National Agriculture and Food Research Organisation in Japan. As yet, the benefits have only been seen in mice, but more research may show their effectiveness in humans.
The jury is out on how good sweet potatoes are for us when eaten regularly.
They contain beta-carotene, which boosts the immune system and keeps the skin healthy. But while this makes them more nutritious than regular potatoes, the sweet variety has a high glycaemic load, meaning large portions cause a spike in blood sugar.
However, the new study, published in the journal Heliyon, suggests we have may have been washing the best health benefits down the sink.
The researchers fed three groups of mice high-fat diets, giving one group the protein, called sweet potato peptide, at a high concentration and one group at a lower concentration.
The peptide is made by enzyme digestion of the sweet potato protein from waste cooking water.
These mice ate the ingredient as 5 per cent of their diet over 28 days.
After that they were weighed, and their liver mass and fatty tissue was measured as well as levels of fats and hormones.
The mice on high-fat diets given the highest level of sweet potato peptide saw their cholesterol drop 7.2 per cent compared with those who were denied it.
Triglycerides, which come from fat in the diet and put people at risk of diabetes, fell more than 40 per cent.
The results also showed they lost fat around their middle and were less likely to get fatty liver disease.
Researcher Dr Koji Ishiguro said: ‘We were surprised that SPP [sweet potato peptide] 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 waste water instead of discarding it.’