Barbecue season has arrived and all around the nation home cooks are moving outdoors to socialise with friends and family. But shouldn’t we feel nervous about slapping a big beef steak on the barbecue? After all, the World Cancer Research Fund (WCRF) recommends we limit our red meat intake to reduce cancer risk, specifically colorectal cancer. Fiona Carruthers, Beef and Lamb New Zealand’s nutrition manager, doesn’t buy into the WCRF recommendation. “We’ve always been surprised by the WCRF’s conclusions as we don’t believe the available scientific evidence supports them.”
Carruthers says the work of researchers such as US-based epidemiologist Dominik Alexander is helping us better understand the links between lifestyle and cancer risk. “What has remained clear throughout is the involvement of obesity and a lack of physical activity as the key factors in the increased risk of many cancers.” Alexander co-authored a review last year in the European Journal of Cancer Prevention that questioned the evidence linking red meat to colorectal cancer. His research team analysed 25 studies and found that people who ate the most red meat had a 12% greater risk of the disease. When they looked at the data by gender, men had a 21% greater risk and women just 1% more. But although researchers have explored gender differences in diet, hormones and biology, they haven’t found a plausible explanation for a gender-based risk difference.
What is certain is people who eat a lot of red meat tend to be heavier and have bad habits. They’re also likely to smoke, drink too much alcohol, not exercise enough, have a low fruit and vegetable intake and be comparatively poor – all factors that increase colorectal cancer risk. Given the small effect, unexplained variations in study findings and possible confounding by other dietary and lifestyle factors, Alexander wasn’t prepared to link red meat consumption with increased risk of the cancer. However, the WCRF’s 2011 update on diet and lifestyle factors associated with colorectal cancer says there is a 17% increase in risk per 100g of red meat eaten a day, down from the 29% risk it calculated in 2005.
It says that given existing evidence of a relationship between the amount consumed and the body’s response, and plausible explanations for how red meat may cause biological changes that increase cancer risk, it remained convinced it is a cause of the disease. So, how can two parties have such divergent opinions on similar data? The criteria used for proving cause and effect are only a set of guidelines and not definitive, so they’re open to interpretation, says Rod Jackson, an epidemiologist at the University of Auckland. Different reviewers are free to emphasise different criteria. “When the effects of a risk factor are relatively weak, as they are with red meat and colorectal cancer, it’s common for there to be conflicting interpretations.”
Alexander’s review was funded by a consortium from the US beef and pork industry. “There’s evidence from systematic reviews that industry-funded studies and reviews are more likely to present findings that support their products than equivalent studies and reviews that aren’t industry-funded,” Jackson says. Still, Alexander isn’t the only epidemiologist to publicly question the WCRF’s red meat conclusions. Jackson says the risk reported by both Alexander and the WCRF can’t be considered definitive when based on observational studies, as opposed to randomised trials, because it could be a spurious relationship.
“In my opinion the evidence isn’t definitive but it appears the WCRF has taken a ‘first do no harm to consumers’ approach, and given the evidence is suggestive of harm, it has wanted to warn people about this. In contrast Alexander appears to have taken the ‘innocent until proven guilty’ approach, or perhaps ‘first do no harm to industry’ approach.” The cautious approach would be to stick to the WCRF recommendation of eating no more than 500g of cooked red meat (700-750g raw weight) a week. That means beef, lamb or pork can safely be enjoyed three to four times a week alongside plenty of fresh salads this summer.