MARIKA SBOROS: What's the beef with cancer and bacon?

Just one slice of bacon a day raises your risk of bowel and colon cancers by about 20%, say UK scientists. The same applies to moderate intake of red meat, say the University of Oxford researchers.

Their recent study in the International Journal of Epidemiology is the largest ever UK  investigation of the risks. The researchers tracked the diets of nearly 500,000 UK men and women aged between 40 and 69 over five years.

Their study went viral. It has put more flesh on the bones of anti-meat lobbies and added grist to the mill of plant-based lobbies worldwide. It has bulked up the body of evidence purporting to show that both red and processed meats are carcinogens (cancer-causing agents).

But do meat-loving South Africans really need to worry?

Some experts say the Oxford study confirms previous findings that consumption of red meat and processed meat, such as bacon, ham and sausages, increases the risk of colorectal cancer. And since 2015, the World Health Organisation (WHO) has classified processed meats — as a Class 1 carcinogen and red meat as “probably carcinogenic to humans”.

Other experts say the Oxford study is fear-mongering by plant-biased researchers. They say the study is riddled with flaws that undermine its conclusions. They also say there is no robust RCT (randomised, controlled trial) research whatsoever to show that red meat causes or even raises cancer risk. RCTs are the “gold-standard” of scientific research.

The only evidence for both red and processed meats, they say, is epidemiological (population-based, the weakest form of evidence as it is associational and, therefore, can only show association, not causation).

Epidemiological nutrition research also relies heavily on notoriously unreliable self-reporting via food-intake questionnaires. People don’t always correctly recall what they ate over years or just don’t tell the truth.

The Oxford researchers claim to have made “extra adjustment” to ensure accurate reporting by participants. They acknowledge red meat’s nutrition benefits. However, even participants whomore or less adhered to official government dietary guidelines to eat an average 76g of red or processed meat per day had a 20% increased risk of bowel cancer compared with those who averaged just 21g daily.

Their findings also showed a higher colorectal cancer risk (up to 24%) in heavier alcohol drinkers compared with those who drank less.

UK public health researcher Dr Zoë Harcombe said that the Oxford study suffered the same three limitations of all epidemiological studies: association, not causation; relative, not absolute risk; and the healthy person confounder. The unhealthy person confounder — the heavy red-meat eat or burger monster as Harcombe put it — tends to be less healthy overall.

The researchers also consistently lumped red and processed meat together: “This happens with virtually every paper attacking meat.”

There is no evidence against red meat alone, Harcombe said. It is reported with processed meat to “try to condemn red meat by association”.

The study did find a tiny association — not causation — with processed meat and bowel cancer and red and processed meat lumped together and bowel cancer — driven by processed meat — but not red meat and bowel cancer, Harcombe said.

“I've yet to find any evidence against red meat for any actual health outcome. It would make no sense, from evolution, for there to be any.”

The study was interesting for several “non-findings”, which tell us what’s not associated with bowel cancer, Harcombe said. Among these: a higher total fibre was not associated with lower bowel cancer but higher fibre in bread and cereals was claimed to be associated with lower bowel cancer.

“That tells us that fibre per se can’t be the benefit,” she said. That raises the question whether the benefit could be nutrients added to bread and cereals — which just happen to be found in meat.

The researchers also gave no plausible explanation for any association with processed meat and bowel cancer. They appeared to assume that it’s simply accepted that meat causes cancer, Harcombe said. 

“Even if this were causal, which it isn’t, the absolute difference boiled down to just over one case of bowel cancer a year in 10,000 people when comparing consumption of three rashers of bacon with one rasher a day.”

Dr Melissa Wallace, Cancer Assocation of SA (CANSA) research head, said that the trends seen in the Oxford study are not new. “However, this research highlights the importance of consumption awareness, particularly the quantity of red and processed meat consumed,” Wallace said.

The researchers considered the effect of various confounding factors, such as alcohol and physical activity but not others, such as the intake of vegetables and fish.

“It would be of interest to investigate these factors, as well the cooking methods used, to further determine the possible extent of cancer risk from red meat.”

CANSA supports the best available scientific evidence and population goals from the World Cancer Research Fund (WRCF) Third Expert report 2018 research, she said. The WCRF population goal: to limit consumption of red and processed meats to three or fewer portions weekly, not more than 350g-500g of cooked meat weekly and to consume little, if any, processed meat.

“More local research is required that considers SA’s diverse population and possible causes of colorectal cancer.

“Recommendations to limit meat intake, particularly in processed forms, should be considered in the context of a healthy, balanced diet consisting mainly of vegetables and fruit, with limited sugar and alcohol consumption, and encouraging physical activity,” Wallace said.