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Debunked: Cheeseburger as bad as smoking

New research claiming that a double cheeseburger might be as risky as lighting up a cigarette may have caused protein lovers to choke on their milkshakes. Relax. Despite the ominous-sounding conclusion from a University of Southern California press release that too much dietary protein raises the risk of dying of cancer in middle age, there's actually very little valid information to back up the findings.

Some of the new research is consistent with the current thinking that diets high in animal fats can increase chronic disease risk, and that long-term consumption of a plant-based diet can reduce the risk of chronic illness and death. The other conclusions are only theories, not fact.

By combining epidemiologic data in humans, preliminary mice studies, and laboratory cell studies, the researchers have “connected the dots” in a series of explanations which do not hang together as an evidence-based concept. The report, which was published earlier this week in Cell Metabolism, attempts to find a cause-and-effect relationship of dietary protein and cancer risk, but fails. 

"The headline of the press release from the University of California is running ahead of the evidence and the comparison with smoking is really unwarranted in terms of the relative risks and the certainty of the adverse effects of smoking," says Tom Sanders, head of the Nutritional Sciences Research Division, King’s College London. 

Examining the well-studied NHANES database reveals further limitations with the study’s conclusions. The number of people selected from this very large database was relatively small — an estimated 6,000.

While the dietary protein intake was self-reported, there was no distinction between animal proteins that are healthy (fish or skinless chicken) or those containing high amounts of saturated fats (fatty red meats). This is a major concern, and limits the conclusions of the results.

“Sending out statements such as this can damage the effectiveness of important public health messages," says nutrition scientist Gunter Kuhnle of the University of Reading. "They can help to prevent sound health advice from getting through to the general public."

Rather than be alarmed over protein, the takeaway should be: a diet containing high quality proteins, rich in fruits and vegetables, with a focus on plant-based eating is recommended and supported by science.

[Editor's note: An earlier version of this story stated that the University of Southern California research did not account for factors among the participants such as obesity and BMI, smoking and socioeconomic status.]