A study involving 11 volunteers found that a bowl of watercress soup each day, in addition to a high-carbohydrate breakfast and a high-protein supper, helped to promote weight loss.
On average, dieters lost more than one stone in a matter of weeks, indicating that the addition of watercress to people's diets could help to fight festive flab.
Tom Amery, managing director of the Watercress Company, told Farming UK: "We're thrilled with the result of the diet.
"Apparently the average person gains 7lbs over the Christmas period, so if you find your clothes a little snug in the new year then try cooking up some watercress soup."
Watercress provides other health benefits in addition to apparently supporting weight loss, as it is high in iron, calcium and folate, as well as vitamins A and C.