After numerous newspapers claimed burnt toast could cause cancer, Dr David Robert Grimes peers behind the headlines of health research coverage.
From the broadsheets to the red-top tabloids, at the end of January, the press went into overdrive following the launch of a Food Standards Agency campaign about the possible health risk of acrylamide, which is created when starchy foods are roasted, grilled or fried for long periods, at high temperatures. The coverage ranged from the headline “Stop! Don’t Toast that Bread” to a call for restaurants to stop fluffing their potatoes.
Following this, The Biomedical Scientist asked Dr David Robert Grimes, an award-winning cancer researcher, to analyse newspaper headlines and claims about studies relating to food and cancer.
STUDY 1
- Newspaper headline: “Now EU bureaucrats tell us we can’t eat TOAST”
- Newspaper claim: “An EU watchdog says toast should be eaten only when it is a light brown colour or it could increase the risk of cancer”
DR GRIMES SAYS: “This screaming headline is an example of a red-top paper skewing good advice to beat an ideological drum. In experimental animals, acrylamide has been demonstrated to cause certain types of cancer. However, the picture is less clear in humans, where studies have thus far failed to show a clear link between acrylamide and carcinogenesis.
As a result, acrylamide is classified by the IARC as a Class 2A carcinogen (see case notes below). This means while there is inadequate evidence of carcinogenicity in humans, the potential for causing cancer has been demonstrated in animals and there is strong evidence similar mechanisms might impact humans. Naturally enough, it isn’t added to food; however cooking certain foods at high temperature (>120°C) can cause a chemical reaction which yields acrylamide.
“This reaction typically occurs in starchy foods, such as bread, chips, and cake. The advice from the EU and UK food safe authorities is simply a precaution to avoid potentially detrimental intake, even though the absolute risk factor is quite low. In any case, many of these foods are in themselves unhealthy, and as obesity is itself a stronger risk factor for cancer, so such advice is not unwelcome.”
DR GRIMES' CASE NOTES
The IARC classification on cancer is controversial, and often misunderstood. It does not quantify how much exposure to a carcinogen is required to induce cancers – the fact something might be a carcinogen does not give one information on acceptable levels, nor of its absolute risk.
There is a tendency for media outlets to fixate on research findings without consideration of what they mean. As science is a perpetual process of self-correction, it is not unusual to have research findings that conflict. This means that caution must be exercised in interpreting results.
It is also vital to realise that cancer is an entire class of diseases with varying prognosis, causes and treatments. It is overly reductive to treat them all as self-similar, and the notion of a “magic-bullet” cure is understandable, but utterly wrong-headed.
STUDY 2
- Newspaper headline: “Eating handful of nuts a day can keep the doctor away, research proves”
- Newspaper claim: “Being nuts about nuts reduced the risk of heart disease by nearly 30%, the risk of cancer by 15%, and the risk of premature death by 22%”
DR GRIMES SAYS: “A balanced diet is vital to maintaining one’s health – but we need to be wary of grandiose claims, and conscious of confounding variables. The study in question was a meta-analysis of other studies, which concluded that nut consumption might reduce cancer mortality. However, the limitation of population studies is that other confounding variables can skew the analysis – for example, people who consume more nuts might have a better diet or lifestyle in general, and further research could be needed to discriminate which factors truly contribute.”
STUDY 3
- Newspaper headline: “Booze DOES increase your risk of deadly skin cancer – but white wine is the most dangerous tipple”
- Newspaper claim: “Each daily glass of your favourite sauvignon blanc or pinot grigio raised chances of melanoma by 13%, experts found”
DR GRIMES SAYS: “Alcohol consumption has a known association with some cancer types. The mechanistic reason for this is thought to be the production of acetaldehyde from ingested ethanol. This chemical can damage DNA, rendering it an established carcinogen. The study here found a very modest association between alcohol and melanoma, which probably isn’t all that surprising. Given alcohol itself leads to acetaldehyde production, the link with white wine seems rather tenuous, and could just be a statistical artifact.”
STUDY 4
- Newspaper headline: “Liver cancer breakthrough: Drinking coffee ‘reduces risk’ of developing killer disease”
- Newspaper claim: “Coffee can reduce the risk of developing liver cancer, experts have revealed in a new scientific review – with research suggesting the benefits could be greater the more they drink”
DR GRIMES SAYS: “This is yet another example of a media outlet overstating the results of a study. This meta-analysis found that coffee intake appears to have an inverse relationship with liver cancer incidence. However, as with the nut consumption study, there are limitations to what conclusions one can draw – correlation does not prove causation and more refined methods are needed to determine mechanistic connections. As the authors point out, most of the studies they looked at did not adjust for other factors, such as sex, alcohol, BMI or history of liver disease, prompting to authors to remark ‘…the presence of unmeasured confounding inherited from original studies may be a matter of major concern’.”
STUDY 5
- Newspaper headline: “Can coffee cause cancer? Only if it’s very hot, says WHO agency”
- Newspaper claim: “IARC presented other scientific evidence which suggests that drinking anything very hot – around 65°C or above – including water, coffee, tea and other beverages, probably does cause cancer of the oesophagus”
DR GRIMES SAYS: “Hot beverages are also a class 2A carcinogen, with the IARC stating that ‘…although the mechanistic and other relevant evidence for very hot beverages is scant, biological plausibility exists for an association between very hot beverages and cell injury and the sequelae that might lead to cancer’. While the human evidence is sparse, high temperatures can be cytotoxic and lead to cell death, which might be a mechanistic reason for this to occur.”