Myth of the Month: "Purple tomato can beat cancer"
"Purple tomato can beat cancer" was the headline to a front-page story in the UK paper the Daily Express, which claimed that scientists at the John Innes Centre had genetically modified tomatoes with genes from a snapdragon plant to create "the ultimate healthy superfood". According to the Express, the GM tomato, because of its increased antioxidants, could protect you against cancer, keep you slim, ward off diabetes and help you safeguard your eyesight. There was also enthusiastic coverage of the GM tomato on the BBC TV Horizon programme, the BBC Radio 4 Today programme, CNN, CBS, ABC, Reuters and the UK tabloid and broadsheet daily and Sunday newspapers, amongst many other media outlets worldwide.
However, the UK's National Health Service (NHS) and Cancer Research UK (CRUK) both expressed strong reservations about the coverage of the story. According to an article in NHS Choices, reporting the views of the NHS Knowledge Service: "These claims are not actually based on benefits seen in humans, but rather from a small-scale study of mice that were given an extract of genetically modified tomatoes." The NHS Knowledge Service also notes: "The small sample sizes used mean the results may have occurred by chance. Also until the tomato is tested in humans we cannot be sure that it will offer the same benefits, or that there will not be any unexpected harms.” It concluded that without further research the claims that these GM tomatoes "can beat cancer" cannot be supported.
Cancer Research UK noted on its Science Update blog that "cancer is a complex disease that has lots of 'causes'... The problem with a lot of the coverage of the super-tomato story is that it misses out on this complexity... There's also a big - and in our opinion unwarranted - assumption in some of the coverage. And that's the simple equation that antioxidants = good. There's a fair amount of evidence that some antioxidants in our foods can help prevent some kinds of cancer in some people. But the complexity of this evidence often gets translated in the media and in advertising to 'antioxidants prevent disease'. And that's not what the science says." 
It's worth noting that the dubious claims about purple tomatoes and cancer and the simplistic claims about antioxidants originated with the media work of the John Innes Centre ("Purple tomatoes may keep cancer at bay"). They were not made up by the press even if they were reported uncritically. And the John Innes Centre also appears to have made no effort to play down or otherwise correct the claims that were made as a result of its media work. In fact, it seems to have welcomed and encouraged the PR impact from the coverage. For example, one of the researchers involved wrote an article for the Daily Mail which was headlined, "How my purple tomato could save your life".
While the researchers may not have been responsible for the headline, far from seeking to rectify any of the hype or misinformation arising from their claims, the JIC clearly saw the coverage of the purple tomato story as an excellent means of promoting GM. A front page piece in a JIC house publication noted enthusiastically: "Our research has been reported very positively world wide... and has already had a societal impact in the UK, helping re-frame the GM debate."
A good example of how the upbeat coverage was achieved is provided by Professor Cathie Martin's comment in the JIC's press release that, "The next step will be to take the preclinical data forward to human studies with volunteers to see if we can promote health through dietary preventive medicine strategies." But in a more measured press release from one of the JIC's collaboarators in the research - the Universita Cattolica del Sacro Cuore - Marco Giorgio from the European Institute of Oncology warns, "We have to consider that in this study we have not taken into account any possible toxicity so I shall say we're far from considering a human trial."
It's also worth noting that significant levels of the antioxidant (anthocyanins) which led the GM tomato to be described as the "ultimate healthy superfood" already occur naturally in a whole range of common fruit and vegetables, including raspberries, blackberries, blueberries, bilberries, red cabbage, red onions and aubergines (eggplants). The JIC researchers argue that tomatoes are consumed by people who might not normally consume these fruits and vegetables. It is questionable, however, whether people who are so conservative in their food choices would be attracted to a tomato with a highly unconventional appearance - one newspaper described it as looking "like a cross between an orange and a black pudding." And Dr Lara Bennet of CRUK warns that in any case, "it is too early to say whether anthocyanins obtained through diet could help to reduce the risk of cancer".
1. Victoria Fletcher, "Purple tomato can beat cancer", Daily Express, 27 October 2008
2. "Purple tomatoes 'beat cancer'", NHS Choices, 27 October 2008
3. Lisa Melton, "The antioxidant myth: A medical fairy tale", New Scientist, 5 August 2006
4. "Purple tomatoes won't beat cancer", Cancer Research UK Science Update blog, undated
5. "Purple tomatoes may keep cancer at bay", press release, John Innes Centre, October 2008
6. Cathie Martin, "How my purple tomato could save your life", Daily Mail, 8 November 2008
7. "Purple tomatoes - A GM research tool with worldwide appeal", Advances, John Innes Centre and Sainsbury Laboratory, Issue 12, Winter 2008-9
8. "Purple tomatoes may keep cancer at bay", press release, John Innes Centre, October 2008
9. "Purple tomatoes: The richness of antioxidants against tumors", press release, UniversitÃ Cattolica del Sacro Cuore, 12 November 2008, archived on the website of the Institute of Tropical Disease, Airlangga University
10. Mike Philpott, "What the papers say", BBC News, 27 October 2008
11. "Purple tomatoes 'beat cancer'", NHS Choices, 27 October 2008