When the Archives of Internal Medicine published the article “Red Meat Consumption and Mortality” all I could think of is “here we go again.”
First to go through this paper- which is a statistical population study from the Health Professionals Follow-up Study (HPFS) and the Nurses’ Health Study (NHS). Of the 140,000 combined participants they tossed out 20,000 because of a history of the diseases reported or those who did not fill out the forms perfectly.
To start with – this is not a study where people were followed from baseline to death to see if what they ate contributed, and determining amounts along with following other variables as they progress (lifestyle issues with exercise, smoking, etc). This instead is a study based on food questionnaires, and statistical analysis. Correlation does not imply causation.
One has to be careful with epidemiological studies, as they are not proof of a cause, rather they point to a number of variables that might be involved to form a hypothesis. It is these same types of statistical studies that told us that women should use hormone replacement therapy because it prevents heart attacks in 1991, only to be told 11 years later that it might cause heart attacks. It is a sampling bias of those individuals who choose to participate in the studies that led to the erroneous conclusions.
The second issue with these studies is the ability of the food questionnaire and its accuracy. This has been studied – that is, the ability of people to recall and fill out what they ate. We do this in our office all the time- ask people what they eat—and since we are involved in weight loss and healthy lifestyle here is what we can say: people have no ability to remember what they ate, how much they ate much beyond the last day. When studied by others, looking at the questionnaire (FFQ or Food Frequency Questionnaire) in the Nurses’ Health Study was found to be useless. As reported by others, the accuracy of the questionnaire compared to reality was unacceptable.
For example, 20 per cent of the nurses reported living on 1200 calories per day or less, and low intake of red meat, and 20 percent report over 2000 calories a day.
In the study the first table showed that the highest reported red meat consumption was associated with smoking, drinking more, obesity, and higher calories. Oh wait- have you ever heard that smoking, obesity, eating more calories, or drinking more might lead to an early death? Perhaps you have, in fact, there are some correlations (which don’t imply causation) for these, and there are some great prospective studies showing that obesity leads to early death. Of course, in any statistical paper you can remove the confounding factors – and THEY DID NOT in this paper.
One other cute correlation- in the data, those who report eating the most red meat had the lowest cholesterol levels. Yes, that is odd isn’t it. Readers of this blog know that cholesterol and meat have less to do with one another – and that isn’t a statistical issue, that is just basic biology. Eating more meat does not mean you will have a higher cholesterol – having bad genetics does.
Here is what three systematic reviews of prospective studies show in the relationship between saturated fat and heart disease- zip. There has been a consistent lack of an associated between saturated fat intake and heart disease. While this new study statistically makes the argument that changing diet would decrease events from heart disease and cancer, when looked at (references below) none of the pooled studies show a change in that risk relationship. And, when some studies have shown a change in risk, when the data was examined there was no difference in mortality. While some say red meat clearly is bad, the evidence is anything but clear. Proving again that population studies, without isolating the variables, without having a scientific basis, are worthless.
Finally, the science of red meat—what do we know? Red meat is a large category of meats includes everything from bacon (considered “processed” by some and delicious by others) to cows raised on grain, and cows raised on grass. Grass fed beef have higher levels of omega-3 fatty acids. Consuming different red meats mean you are consuming different levels of ingredients. Lumping them together is just sloppy science. For part two of this click here.
Skeaff CM, Miller J. Dietary fat and coronary heart disease: summary of evidence from prospective cohort and randomised controlled trials. Ann Nutr Metab 2009;55:173–201.
Mente A. A systematic review of the evidence supporting a causal link between dietary factors and coronary heart disease. Arch Intern Med 2009;169:659–69.
Siri-Tarino PW, Sun Q, Hu FB, Krauss RM. Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. Am J Clin Nutr 2010;91:535–46.
Dr. Terry Simpson
Dr. Terry Simpson received his undergraduate and graduate degrees from the University of Chicago where he spent several years in the Kovler Viral Oncology laboratories doing genetic engineering. He found he liked people more than petri dishes, and received his MD. Dr. Simpson, then became a renowned weight loss surgeon, and a leading advocate of culinary medicine. The first surgeon to become certified in Culinary Medicine, he advocates teaching people to improve their health through their food. On the other side of the world, he has been a leading advocate of changing health care to make it more "relationship based," and his efforts awarded his team the Malcom Baldrige award for healthcare in 2011 for the NUKA system of care in Alaska. A frequent contributor to media outlets discussing health related topics and advances in medicine, he is also a proud dad, husband, author, cook, and surgeon “in that order.” For media inquiries, please visit www.terrysimpson.com.