Patients bombard doctors with requests for dietary tips, but GPs are often just as much in the dark.

Dr Margaret Rayman said: "A lot of doctors have told us that they have been practising nutritional methods to some extent but they feel they are flying by the seat their pants.

"They never had a grounding in nutrition and they just picked up what they could."

Nutritional issues

Dr Rayman has started a course at the University of Surrey that is the first in the UK to teach doctors how to use nutrition to treat and prevent disease.

Folic acid is recommended during pregnancy

She said that the right diet can help prevent conditions such as cancer, diabetes, heart disease and dementia.

Thirty pupils have signed up for the postgraduate course, which will take two to six years of part-time study to complete.

Dr Rayman said: "Nutritional methods of treating and preventing medicine are powerful, safe and effective.

"I hope with this group of students to bring nutritional medicine into the mainstream of medical practice."

Best research

Dr Rayman said that there was good research into nutritional medicine but much of it gets lost amid a bewildering amount of "rubbish" about how diet affects health.

She said that nutritional medicine is backed up by "excellent quality evidence-based research".

"There is no need to resort to anecdote or mumbo-jumbo - it really is all there," she said.

The point of the course is to clarify what advice doctors and other health professionals should be giving to patients, she said.

"There are ways of eating that are healthy in terms of preventing cancer and coronary heart disease.

"Ultimately there are, on some occasions, supplements that can also reduce the risk of chronic disease," Dr Rayman added.

Training refresher

One of the GPs who signed up for course, Dr Wendy Wallace, said: "I qualified 25 years ago at a time when less was known about nutritional medicine.

The BBC's Catherine Bennett reports

"Things have come on a lot since then with an increasing amount of exciting new research in diet and health.

Dr Wendy Wallace: "Exciting new research"

"I felt I should know about all these new developments which could be of use to my patients."

The benefits of a healthy balanced diet start in the womb, Dr Rayman said.

Apart from the established benefits of folic acid supplements in pregnancy, pregnant women should be aware of the health risks of "underfeeding" a baby in the womb, she said.

"The risk of disease in adult life is much higher, higher risk of diabetes, higher risk of coronary heart disease and higher risk of high blood pressure in later life are associated with poor foetal growth," she said.

She added that it was important that this approach to nutritional medicine spread.

"These are methods that people can use," she said.