Low-fat diets are not the best way to lose weight, a major study says today – casting doubt on decades of health advice.
Scientists concluded there is no evidence to support the dogma that people should reduce the amount of fat in their diet.
Health officials should give simple guidance focused on portion sizes and unprocessed foods instead of focusing on fat, carbohydrates and proteins, said the researchers from Harvard.
Dr Deirdre Tobias, who led the research based on data from more than 68,000 adults, said: 'There is no good evidence for recommending low-fat diets.
In 1983, Government guidelines advised Britons to cut their fat intake to 30 per cent of total energy and increase the amount of carbohydrates they ate.
Emerging evidence suggests that not all types of fat are bad – and some can play a role in protecting the heart and reducing weight.
There is growing interest in Mediterranean diets with high levels of fatty foods such as olive oil, fish and nuts as well as fruit, vegetables and whole grains.
The Harvard team found that cutting back on fat was a less effective route to weight loss than low-carbohydrate or Mediterranean diets.
Those on low-carbohydrate diets lost an average 2.5lb (1.15kg) more than those on low-fat diets over 12 months, it showed.
Dr Tobias called for a move towards healthy eating patterns, whole foods and portion sizes.
Not all experts, however, are convinced. Professor Tom Sanders, of King's College London, said: 'To control weight, it remains sensible to eat less and avoid consuming excess amounts of fat and sugar, especially as fatty meat, deep fried foods, cakes and biscuits and sugar-sweetened beverages.'
In a commentary in the journal, Keith Hall, of the National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, US, said a key reason why people failed to lose more weight was that they had often given up before the year was over.