Popular slimming programmes have been given the thumbs-up by researchers.
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Experts analysed the effectiveness and nutritional content of Slim Fast, Atkins, WeightWatchers and Rosemary Conley's Eat Yourself Slim diet.
The Nutrition Journal study found all the diets result in reduced energy intake - helping to control weight - while providing sufficient nutrients.
However, dieters failed to increase significantly their consumption of fruit and vegetables as recommended.
The analysis, based on food diaries compiled by 293 people around the UK, appears in the Nutrition Journal.
Writing in the journal, the researchers said: "This analysis provides reassuring and important evidence for the effectiveness and nutritional adequacy of four commercial diets in weight management for the general public."
The volunteers, who kept a food diary for two months, were compared to a control group, who continued to eat as normal.
The results showed that all the diets resulted in a significant drop in body weight compared to the controls - but there was no significant difference in weight loss between the diets themselves.
However, despite the fact that all of the diets apart from Atkins advise people to increase their fruit and vegetable intake, the researchers found that the only dieters to do so were those on the WeightWatchers diet, and even they only had one more portion a day.
Lead researcher Helen Truby, of the University of Queensland, said: "These disappointing findings suggest that people remain resistant to the advice to 'eat more fruit and vegetables', even when they are advised to as part of a modified weight loss programme."
Nutritional deficiency
Critics of the Atkins diet have suggested that people who follow its low-carbohydrate regime run the risk of becoming deficient in some key nutrients.
The researchers found that Atkins dieters tended to show signs of a reduced level of iron and niacin - probably due to a fall in the intake of cereal and flour.
They also tended to have a low intake of dietary fibre, which is needed to keep the digestive tract healthy in the long term.
But overall, the researchers found little evidence of any detrimental effect from following the Atkins diet - in the short term at least.
On the whole, micronutrient intake remained above recommended amounts for most nutrients on all four diets.
The researchers suggest that commercial companies work with health professionals to identify people at higher risk of nutritional deficiency, and provide them with dietary advice tailored to their nutritional requirements.
Heather Caswell, a nutrition scientist at the British Nutrition Foundation, said: "It is a shame that the diets did not result in an increase in the fruit and vegetable intakes of the subjects, however the fact that subjects lost weight will reduce their risk of many risk factors for diseases such as cardiovascular diseases and also certain cancers.
"My one concern with these choices of diets would be the Atkins diet - the health effects of this diet in the long term are not well known, and I would therefore advise anyone against opting for this diet with a view to helping them to achieve long term weight loss."
