Let me see, is there anything I can eat?

A bombshell report released in the UK has blamed putting on weight, alcohol and a whole range of everyday foods for causing cancer. Consumers were told to curb drinking, avoid processed meats - including bacon, ham and sausages - and cut their intake of red meat and salt.

Even supposedly healthy fruit and vegetables were said to offer only "limited" protection against the disease. The £4.5 million study was done by 21 international experts on behalf of the World Cancer Research Fund. The report offers the toughest advice yet on guarding against cancer.

Its key finding is that being fat is as bad for you as smoking. Excess body fat can trigger at least six common cancers including those affecting the breast, bowel and pancreas. The study found strong evidence that red meat and processed meats can cause bowel cancer while there are strong links between alcohol and mouth, oesophagus and breast cancers.

The experts say there is no safe level of drinking. People who take small amounts of alcohol to protect against heart disease should limit themselves to two drinks a day for men and one for women. The report's guidelines include staying as lean as possible and eating no processed meats and only 500g of cooked red meat a week.

To reach their verdict, the panel sifted through 7,000 of the best studies on cancer, diet and exercise produced over the last 40 years. Professor Martin Wiseman, the project director, said it was a "milestone" that would help people through a maze of conflicting health messages.

He said: "When individual studies are published, it is impossible for the public to put them into context and know how seriously they should be taking the findings. This report does this job for them. The report says the evidence linking obesity and cancer is much stronger than ten years ago, when the WCRF first investigated it. Diet and obesity account for at least a third of cancers - as many as smoking.

The panel found a specific strong link between fat around the abdomen and bowel cancer. There is also a "probable" connection between body fat and gall bladder cancer, and between abdominal fat and pancreatic, post-menopausal breast and endometrial cancers.

The report describes possible ways in which body fat fuels cancer, including promotion of the growth hormones and oestrogen, which can increase the risk of breast cancer. Alcohol may trigger DNA damage leading to cancer. Fast foods high in fat, sugar and calories should be avoided, along with fizzy and sugary drinks. People should drink only one glass of fruit juice a day.

There were mixed messages about dairy products. Milk was thought to protect against bowel cancer and possibly bladder cancer-but high-calcium diets may be a cause of prostate cancer. Breastfeeding, in contrast, protects mothers against breast cancer and children against adult obesity.

The report says exercise lowers cancer risk. People should aim for an hour of moderate activity a day or 30 minutes of vigorous activity.