Suddenly, Sundays do not feel quite so innocent. That bacon you had for breakfast, the roast dinner, the shared bottle of wine, even the urge to stretch out on the sofa – it all now carries a menacing overtone. For although we have been told many times before that the lifestyle so many Britons enjoy might ultimately be our undoing, now we know – we risk cancer unless we change our ways.

Last week’s report by the World Cancer Research Fund brings together the conclusions of 7,000 scientific studies and then makes 10 recommendations for individual changes to minimise risk. In its 537 pages, cancer is revealed to be, to a large degree, a preventable disease. It states that lifestyle could account for a third of all cases, making it the most significant factor after smoking. Given that, in 2005, 153,491 people died of the disease in the UK, that works out as a lot of avoidable suffering.

But the report delivers a puritan prescription for health: 30 minutes of vigorous exercise each day and a commitment to become lean. Little red meat and absolutely no processed meats such as bacon or ham. Little alcohol. No sugary drinks. No fast food. And don’t look to a super-food or dietary supplement to save your skin – this is going to require sacrifice and willpower.

The report’s insistence that we purge ourselves of corrupting influences has to be put in context, however. Take one of the most striking recommendations: that bacon, ham and other processed meats be avoided as there is convincing evidence they increase the risk of bowel cancer. This conclusion is based on 58 studies, 56 of which show a connection. The analysis reveals that someone who eats 50g of bacon a day has a 21% increased risk of getting bowel cancer.

The disease was diagnosed in 36,100 people in the UK in 2004 and 16,092 died from it in 2005. It accounts for 13% of all cancers. But dig into the figures a little deeper and it does not sound quite so gloomy. Only 60 people out of 100,000 are diagnosed with the disease – that is a 0.06% chance of getting bowel cancer each year. For the lover of bacon, with their 21% increased risk, that still only works out at 0.07%. Hold the muesli.

The report’s authority comes from its thoroughness. For five years, 221 experts based in universities and institutions around the world, analysed 7,000 academic papers dating back to the 1960s. A 21-strong panel of leading researchers then drew scientific conclusions from this evidence before agreeing a series of recommendations on minimising the risks.

The starkest recommendations concern weight. The report concludes that there was convincing evidence that excess fat raises the risk of cancer. “Maintenance of a healthy weight throughout life may be one of the most important ways to protect against cancer,” it says.

Accordingly, its recommendations are uncompromising. It is no longer enough to avoid becoming overweight – to reduce the risk of cancer, you now have to be lean. The scientists call for a body mass index (weight in kilograms divided by height in metres squared) at the lower end of the healthy range of between 18.5 and 25. They warn that the sedentary life of many people puts them at risk and recommend 30 minutes of vigorous or 60 minutes of moderate exercise to reduce the risk. “All forms of physical activity protect against some cancers,” they say.

There is, the report declares, no safe level of alcohol. But while it finds convincing evidence that drink increases the risk of cancer, it stops short of recommending abstinence. Sir Michael Marmot, professor of epidemiology and public health at University College London and chairman of the report’s review panel, says that while the risk factors are also broadly applicable to heart disease, alcohol is the one exception.

“From the point of view of cancer prevention, the best level of alcohol consumption is zero,” he says. “This is not the case for cardio-vascular disease, where the evidence suggests that one or two drinks a day are protective.” In a solitary instance of compromise, the report recommends no more than two drinks a day for men, one for women.

Drinks with added sugar are out and even fruit juice limited to a glass a day. Consumption of coffee is declared as unlikely to be a problem while milk probably decreases the risk of bowel cancer, although too much calcium increases the risk of prostate cancer.

While red meat has a convincing link to bowel cancer, the report suggests that – unlike bacon and ham – it can be a valuable source of nutrients and so allows up to 500g a week. Processed, convenience and fast food should be avoided as should anything smoked, grilled or barbecued, which increase the risk of stomach cancer.

The report recommends at least five portions of different-coloured, nonstarchy vegetables and fruits a day . “These, and not foods of animal origin, are the recommended centre for everyday meals,” the report unsurprisingly concludes.

This spartan existence might seem rather extreme. But it would be a mistake to regard the report as a rulebook for life, says Lesley Walker, Cancer Research UK’s director of cancer information.

“If you wanted to minimise your chances of dying in a road accident, you might choose never to drive a car, never to travel on a public highway or even never to walk down your local high street,” she says.

“The report has come up with a series of recommendations that, if followed, would reduce the risk of cancers related to excess weight. It is not telling people what to do; it is assessing risk and suggesting how individuals could choose to minimise it.”

John Adams, emeritus professor and an authority on risk at University College London, having now analysed the absolute risk of getting bowel cancer, declares he has every intention of continuing with his existing diet. “I actually found the report reassuring,” he says. “But I won’t be eating bacon – I prefer a juicy steak.”

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