Researchers from a number of UK universities asked nearly 300 people to keep a diary of their food intake both before and during a two-month diet period.
They found that people on the Slim Fast, Atkins, Weight Watchers or Rosemary Conley's 'Eat Yourself Slim' Diet & Fitness Plan decreased their energy intake.
All of the diets brought about a significant fall in body weight compared to a control group who did not diet, and there was no noticeable difference in the amount of weight loss achieved between the four diets.
The study, which is published in Nutrition Journal, also found that contrary to previous claims, people on the Atkins diet did not experience short-term detrimental effects as a result of eating few carbohydrates.
However, they tended to have lower iron and niacin levels, as well as a lower intake of dietary fibre.
In conclusion, researcher Helen Truby said that the findings provide "reassuring and important evidence for the effectiveness and nutritional adequacy of the four commercial diets tested".