“Doesn’t meat cause cancer?” I hear this comment often enough from people. I don’t blame anyone for thinking this. This line of reasoning has been drilled into us along with a host of other healthcare/dietary myths for years. But the real question is why? YOU NEED TO UNDERSTAND WHERE THIS INFORMATION CAME FROM IN ORDER TO MAKE HEALTHY EATING DECISIONS. The idea that meat causes disease comes from a very large observational study called the Harvard Nurses Study. Here is the most recent “Meat causes cancer” study published in JAMA just this past April.
Remember, though, we learned about observational studies the other day. Observational studies look back in time to try to pick up patterns. They are terrible at determining causation. In fact, the Nurses Study uses what is called a “food frequency questionaire.” This is a questionaire handed out to all the participants in the study — in this case over 100,000 nurses since 1976. They are asked to recall what they ate in the last few months and approximately how much. This should raise a red flag immediately. How many of us remember what we had for lunch last Tuesday? Right. Me neither (although I know it was healthy!). There are some very smart people who would like to eliminate the use of the “food frequency questionaire” in dietary studies. It is a cheap way to gather data and that is about the only advantage. The information is not very accurate.
The Nurses Study looked at other behaviors as well. Things such as smoking, alcohol intake, exercise patterns, etc. Finally, the study looked at health problems. It kept track of cancer, heart disease, mortality, etc. All very important things when you are trying to tell people how to eat. When you are looking at an observational study like this, particularly when it takes place over the course of 20-30 years, you have to account for “compliance bias.” There are people (believe it or not) that listen to what health professionals tell them. They exercise, abstain from smoking/alcohol, get the right amount of sleep, etc. You can imagine that in the early 1980’s, when the USDA adopted its disastrous food pyramid, that health conscious people immediately cut back on meat and increased their carbohydrate consumption. Gary Taubes does a wonderful job explaining compliance bias in this blog post.
“So what Dr. Hoop. Cut to the chase.” OK. When the people at Harvard gathered the data from the Nurses Study, they determined that “eating meat” will increase your disease risk by 0.2 fold. “Dr. Hoop, that does not seem like a very big number.” You are right. To put this in perspective, smoking would increase your risk by 20-fold. Most good scientists will not accept a risk adjustment less then 3 or 4. “OK, Dr. Hoop. But I’ll take a 0.2 reduced risk for disease by abstaining from eating red meat.” Hold on! Remember all those confounding variables! In fact, the people who ate red meat, were also the people who smoked, drank, did not exercise and probably did other things that were not healthy. There is a blog post from Dr. Andreas Eenfeldt in Sweden that captures this in the study that was published in April of 2012. It is worth scrolling down and looking at all the confounding variables.
This is what I would LOVE TO KNOW, but probably never will know. How much longer those people in the “Less Meat” column would have lived had they actually eaten LCHF. In other words, had they NOT listened to the prevailing low-fat theory, they would have lowered their disease risk FAR GREATER then 0.2. They did everything else to maintain their health. I believe that the people who ate more meat (as determined by the “Food Frequency Questionaire”), had a 0.2 greater risk for disease because of their other health habits (smoking, lack of exercise, alcohol, etc.). Eating meat was probably the only healthy thing they were doing. And, if you remember the compliance bias, the only reason they were eating meat is because they were ignoring what was “supposed” to be healthy at the time.
To those of us who advocate and promote the LCHF diet, to see the Nurses Study used to perpetuate the fear of eating meat is beyond frustrating. Robb Wolf recently posted his disgruntlement on his blog. It is an observational study only. Yet so many people have been convinced that meat is dangerous because of this study. It is a belief, for many people, that probably will not change very soon. Do not let this study fool you!