Researchers discovered that eating a diet rich in unsaturated fats, such as those found in walnuts and olive oil, could be as effective for helping people lose weight as a low fat, high carb diet.
They also found that a walnut-rich diet could positively impact cholesterol levels.
Study author Dr Cheryl Rock, from the San Diego School of Medicine at the University of California, said: "Considering the results of this study, as well as previous walnut research on heart health and weight, there's something to be said for eating a handful of walnuts a day."
Researchers analysed 245 overweight women aged between 22 and 72. All of the participants were enrolled on a year-long weight loss programme.
The women were randomly assigned to one of three different diets.
The first was a low fat and high carb diet; the second was a low carb and high fat diet; and the third was a walnut-rich, high fat and low carb diet.
Women on the latter diet would consume roughly one handful and a half of walnuts per day (43g).
Six months later, researchers weighed the women and found that all of them had lost weight.
Those eating a walnut-rich diet lost similar amounts of weight to those from other diet groups - but with the added benefit of improved cholesterol levels.
There was a significant decrease in LDL cholesterol (also known as the "bad" cholesterol) and an increase in HDL cholesterol (the "good" cholesterol). This did not occur within the other diet groups.
Dr Rock said she was "surprised" by the findings, and added: "Even though walnuts are higher in fat and calories, the walnut-rich diet was associated with the same degree of weight loss as a lower fat diet."
Researchers noted that the walnut-rich diet provided more polyunsaturated fats than other diets.
Previous research from Harvard suggested that polyunsaturated fats could improve longevity and lower the risk of heart disease.
The new study does, however, have some limitations.
Firstly, the sample only included women, which means the results may not apply to men.
Secondly, although 245 participants were enrolled, the sample sizes for comparisons were reduced because the participants were divided into subgroups.
And thirdly, there is a lack of detailed information about dietary intake and how firmly people stuck to the diets.
Dr Rock added: "In addition to these findings, we hope to explore the effect of walnuts on satiety, as we believe satiety is a critical factor for maintaining weight loss."
The study was published in the American Heart Association journal.