If you thought your five portions of fruit and vegetables a day was keeping cancer at bay, think again.

Consuming them will not protect you from cancer as they have little effect compared with alcohol and obesity, according to a new study.

The review looks at a decade of evidence on the links between fruit and vegetables and the development of cancer, but it concludes that the evidence is still not convincing.

The researchers discovered that only diet-related factors that definitely affect cancer risk are obesity and alcohol.

Tobacco is still the single biggest cause of cancer.

While smoking increases the risk of cancer by as much as 50 fold, even large consumptions of fruit and veg will only reduce the risk by a maximum of 10 per cent.

Professor Tim Key, an epidemiologist from Oxford University, said that while there are undoubted benefits in eating fruit and vegetables there is little hard evidence that they protect against cancer.

But the evidence is indisputable that cancer is strongly linked to being overweight or obese, and drinking more alcohol than the recommended daily limits.

“Fruit and vegetables are an important part of a healthy diet and a good source of nutrients,” the Telegraph quoted him as saying.

“But so far the data does not prove that eating increased amounts of fruit and vegetables offers much protection against cancer.

“But there’s strong scientific evidence to show that, after smoking, being overweight and alcohol are two of the biggest cancer risks,” he added.

The professor concluded: ‘At least in relatively healthy, well-nourished Westernised populations, a general increase in total fruit and vegetable intake will not have a large impact on cancer rates.

‘For bodies giving advice, it might be helpful to remind people that the things that are absolutely definite are smoking, alcohol and obesity. These are the things to act on for a definite benefit.’

He added that while fruit and vegetables have other health benefits, for those who already have a healthy diet, ‘the evidence does not support eating a lot of fruit and vegetables to reduce the risk of cancer’.

Sara Hiom, of Cancer Research UK, said: ‘Too few people know about the significant cancer risks associated with obesity and drinking too much alcohol.

‘While stopping smoking remains the best way to cut your chances of developing cancer, the importance of keeping a healthy weight and cutting down on alcohol shouldn’t be overlooked.’

The Department of Health recommends eating five portions of fruit and vegetables a day for all-round health.

Victoria Taylor, of the British Heart Foundation, said: ‘There is still good evidence that this helps to lower heart disease risk.’