Forget fad diets - the most effective way to lose weight is by simply eating less fat and taking more exercise, a study has found.
The "not rocket science" weight loss formula achieved results in a large proportion of 2,500 obese Americans.
Forty per cent managed to shed 5% or more of their weight, and 20% lost a tenth or more over a period of 12 months.
Before losing weight, all had a body mass index (BMI) of 30 or more, meeting the clinical definition of obese.
Dr Jacinda Nicklas, from Harvard Medical School, who led the dieting study, said: "This is great news because studies have shown that even a 5% reduction in weight can lead to improved health."
The researchers analysed data from a total of 4,000 obese individuals who took part in a large health and nutrition survey.
Of these, 2,523 reported trying to lose weight.
Writing in the American Journal of Preventive Medicine, the authors concluded: "Those who exercised more and ate less fat were significantly more likely to lose weight."
A correlation was also seen between joining a structured weight loss programme and successfully losing weight.
However, self-reported use of "popular diets, liquid diets, non-prescription weight loss pills and diet foods/products" was not associated with weight loss.
Co-author Dr Christina Wee, from Beth Israel Deaconess Medical Centre in Boston, US, said: "It's very encouraging to find that most of the weight loss methods associated with success are accessible and inexpensive.
"There are lots of fad diets out there as well as expensive over-the-counter medications that have not necessarily been proven to be effective, and it is important that Americans discuss product claims with their doctor before trying such products."