It was commissioned by the World Health Organisation (WHO) and the results are expected to be crucial in making global recommendations.
Report co-author Professor Murray Skeaff, of Otago's Department of Human Nutrition, says the research provides "clear evidence refuting the idea that low-fat diets inherently lead to weight gain".
"The results show convincingly that a lower-fat diet helps control body weight and has favourable effects on other risk factors for cardiovascular disease. This is a very important finding," he said.
Professor Skeaff said the research was important because being overweight or obese increased the risk of many cancers, coronary heart disease and stroke.
Reductions in total fat were also associated with small but statistically significant reductions in cholesterol and blood pressure, suggesting a beneficial effect on other major cardiovascular risk factors.
The review included results from 33 randomised controlled trials in North America, Europe and New Zealand, involving 75,589 men, women and children.
Those taking part had varying states of health. Comparisons were made between those eating less fat than usual and those eating their usual amount of fat.
The effect on weight and waist line was measured after at least six months.
The results show eating less fat reduces body weight by 1.6kg and waist circumference by 0.5cm. All these effects were in trials in which weight loss was not the intended outcome, suggesting that they occur in people with normal diets.
The weight loss happened quickly and was maintained over at least seven years. The researchers say that although "it may be difficult for populations to reduce total fat intake, attempts should be made to do so, to help control weight".
They said high-quality trials were needed to examine the effect of reducing fat intake on body weight in developing countries as well as in children.
Diet tips
• Drink low-fat milk instead of regular milk.
• Avoid butter and cheese.
• Snack on fruit instead of cakes and biscuits.
