"Things that you like to eat cause cancer" was a popular theme in science journalism last week. The caramel coloring in soda was the first alleged culprit, and a study released Monday suggests that eating red meat may cause cancer and cardiovascular disease.
According to CNN, "... the risk of dying at an early age -- from heart disease, cancer, or any other cause — rises in step with red-meat consumption." The media often misreport the conclusions of the research they cover, but this time it appears the scientists involved are encouraging people to eat less red meat.
Are they correct? Probably not. Like most that make headlines, this study was observational and the authors did little to consider any alternative explanation.
For starters, nobody was put on a diet and monitored to see if they developed cancer or heart disease; participants' "[d]iets were assessed through questionnaires every four years" and the data came from two previous studies, the Health Professionals Follow-up Study and the Nurses’ Health Study.
Research like this is entirely dependent upon participants to accurately recall what they've eaten during the period the study is in progress. "In each FFQ (food frequency questionnaire), we asked the participants how often, on average, they consumed each food of a standard portion size. There were 9 possible responses, ranging from "never or less than once per month" to "6 or more times per day."
To get an idea of what it's like to fill out one of these surveys, take a look at the one discussed here. Recording what you eat with any degree of accuracy is incredibly difficult even when you are motivated to do so, as anyone who has ever dieted knows. Now, imagine assessing the food surveys of over 100,000 people for a study spanning slightly more than two decades. Good luck.
The authors defended both the data they utilized and the study's methodology, but the fact remains that observational research doesn't compare to clinical research. And on that score, it is fair to say that red meat in your diet is perfectly healthy, and in greater quantities than those recommended in the current study.
Also noteworthy is the fact that the solid association between meat consumption and cancer and cardiovascular disease is anything but. Many statistical studies of the link between red meat consumption and colorectal cancer, for example, have revealed no correlation between the two. Similarly, as Dr. Michael Eades points out, low-carbohydrate diets (which generally include a lot of red meat) help people avoid these medical conditions.
Additionally, and ironically, previous research has shown that vegetarians don't live any longer than the rest of us, and are more likely to suffer from several serious diseases. Such results are difficult to resolve if red meat is the killer it is made out to be.
Given the shaky nature of the red meat-disease link, maybe there is something else in our diets that is the problem, like sugar. Dr. Robert Lustig, whose research has made him a rather controversial figure, argues that this is indeed the case.
His conclusion is based on the observation that people who become obese and develop diabetes are also more likely to get cancer. The reason being that insulin-resistance (a result of too much sugar consumption) encourages increased production of insulin as well as a related hormone called insulin-like growth factor. According to science writer Gary Taubes, "... the cells of many human cancers come to depend on insulin to provide the fuel (blood sugar) and materials they need to grow and multiply. Insulin and insulin-like growth factor (and related growth factors) also provide the signal, in effect, to do it. The more insulin, the better they do."
Lustig and Taubes are not alone. The relationship between cancer and insulin has been recognized for many years. The World Cancer Research Fund and the American Institute for Cancer Research said as much in 2007, and a number of prominent cancer researchers have come out in support of the hypothesis as well. To be sure, researchers are still fighting over which part of our diets is to blame, and that's precisely the point. It is also something to think about the next time a health story like this makes headlines.
Photo Credit: procsilas