Diet is second only to tobacco as a leading cause of cancer and, along with alcohol, is responsible for nearly one third of cases of the disease in developed countries, a leading researcher said on Tuesday.

Dr. Tim Key, of the University of Oxford, told a cancer conference that scientists are still discovering how certain foods contribute to cancer, but they know that diet, alcohol and obesity . play a major role.

“Five percent of cancers could be avoided if nobody was obese,” he said.

While tobacco is blinked to about 30 percent of cancer cases, diet is involved in an estimated 25 percent and alcohol in about six percent.

Obesity raises the risk of breast, womb, bowel and kidney cancer, while alcohol is known to cause cancers of the mouth, throat and liver, Its dangerous impact is increased when combined with smoking.

Key told the meeting of the charity Cancer Research UK that other elements of diet linked to cancer are still unknown but scientists are hoping that the EPIC study, which is comparing the diets of 500,000 people in 10 countries and their risk of cancer, will provide some answers .

Early results of the study have revealed that Norway, Sweden and Denmark have the lowest consumption of fruit and vegetables among European countries while Italy and Spain have the highest. Eating at least five portions of fruit and vegetables a day is recommended to reduce the risk of cancer.

Key, principal scientist on the EPIC study, said it is looking at dietary links to some of the most common cancers including colorectal, breast and prostate.