All you need to do to lose weight is eat less fat and do more exercise, say researchers.
And the secret to successful slimming is so straightforward it has been dubbed the `Not Rocket Science` diet.
The diet industry is booming, with research suggesting the average woman spends nearly 500 pounds a year on health foods, equipment, clothing and membership fees for gyms and slimming clubs to try to lose weight.
But research suggests there could be a simpler solution.
A team of scientists at Harvard Medical School in Boston studied 4,000 obese adults and found those who followed the common sense advice were much more likely to lose weight than those who adopted fad slimming regimes, went on liquid diets or bought weight-loss supplements.
Two-thirds of the group said they had tried to lose weight in the previous year through a variety of diets.
The researchers found 41 per cent of those who cut their fat intake were more likely to have shed 5 per cent of their body weight in under a year than those who went on liquid diets, used non-prescription dieting supplements or followed popular slimming regimes such as the Dukan or Atkins diets, which combine high protein intakes with relatively large amounts of fat.
And if they exercised more than usual, they were almost 30 per cent more likely to lose the weight, the study found.
Although 5 per cent weight loss may not sound significant, experts say it is enough to delay the onset of diabetes in an obese person.
And the `Not Rocket Science` diet helped many volunteers shed more weight, with 37 per cent of those who cut down on fat more likely to lose a tenth of their body weight, while exercising boosted their chances by 36 per cent.
The researchers did also notice significantly greater weight loss among those who took prescription diet medications, which doubled the chances of 10 per cent weight loss.
But the drugs are not cheap, with the NHS in England spending around 47million pounds a year on medicines to fight obesity.
`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,` the Daily Mail quoted Researcher Dr Christina Wee, who helped compile the study, as saying.
`So it`s very encouraging to find that most of the weight-loss methods associated with success are accessible and inexpensive,` she added.
Dr David Haslam, chairman of the National Obesity Forum, said the `Not Rocket Science` diet sent out `a good message`.
But he added: `Whatever works in the short-term will only be a success if it also works in the long-term. These changes to physical activity and dietary intake have got to be sustainable.`
The study results were published in the American Journal of Preventive Medicine.