Observational studies linking diet to illnesses are, at best, flawed. Usually, an observational study works this way: a sample group of people are asked to fill out a questionnaire which prompts them to remember what they have eaten and in what quantities over a past arbitrary time period. (This is usually filled with memory mistakes- try and precisely tell me how many 3.5-ounce serving of lean red meat you have had over the past 30 days)
Then, researchers let some time go buy (it could be years) and observe who of these people develop the disease they are interested in. They then try to find a correlation between what these people reported as their diet a few years back, and the illness they developed.
It is very difficult to isolate single variables (for example, if you find that people who ate 20+ servings of red meat per month have a 7% increase in atherosclerosis, how can you be certain that the red meat is causing it and not the carbohydrates, alcohol, or poor exercise regime which usually accompany it?)
May I introduce the second most common type of research which tries to inform us on the way humans work: mouse-model studies!
Despite the obvious pitfall, that, er… we are not mice, researchers use these models to try and isolate the previously confounding variables as much as possible, and figure out the mechanism underlying an assumption.
These studies usually go like this: separate mice into several groups. Feed one group diet A (let’s say, standard delicious mouse food) and the other group diet B (standard delicious mouse food + 10% candy cane). Inject them with a known carcinogen, and observe which group develops more tumors.
Then, the researchers publish the paper, and the public hears about it through the media.
ALL FATS ARE NOT EQUAL
Let’s take our present case of high-fat diets. I’m not going to go into observational studies because their results are very weak and questionable, at best. Mouse-based studies, on the other hand, make for great media headlines.
May I present, this Huffington post article:
My problem with these mouse-based ‘high fat’ studies is two-fold: researchers fail to make a difference in what type of fat is used in the titles of their papers, and journalists lack the scientific knowledge to fully understand the research. They write about it and scare people into throwing their butter away and buying margarine. The thing is, all fats are not equal.
Most published studies which have for title: “high-fat diet causes this horrible thing in rats” should be re-named “A corn oil based, high omega-6 diet causes this horrible thing in rats”. For some reason, corn oil seems to be the feed of choice in ‘high-fat’ rat experiments. Well…. OF COURSE a high omega-6 diet will cause more tumor growth in rats. Corn oil is 54% omega-6 and 0% omega-3s. If you leave the rats’ diets unchanged from the control group and just add a whole bunch of omega-6s, no wonder they will get sicker, because Omega-6s increase inflammation. (Have a look at my previous article which explains this in more detail).
Here is the research paper the Huff Post uses as a basis for their article:
A after a little bit of digging into their Materials and Methods section…. what do we find? You guessed it: “Compared with the control diet, our [High Fat diet] has increased caloric content (4,536 kcal/kg vs. 3,726 kcal/kg), which stems from an increase in corn oil-based fat content (1,800 kcal/kg vs. 450 kcal/kg).”
They changed nothing, except quadrupled the amount of corn oil for the High Fat diet group.
Naughty researchers! This is very misleading. Unfortunately, they are not the only ones to put ‘high-fat diet’ in their titles, when they used corn oil. Below are a few more examples:
In this research experiment, rats which had been fed the same diet as the control group + 15% corn oil developed more virulent prostate cancer.
And here, in the first few paragraphs of the paper, you find, blatantly, “fat source: corn oil”.
But hey, research is GREAT. It’s very important to prove through mice-based models that corn oil, because of Omega-6s, promotes inflammation and cancer. It is just dangerous to call a paper “high-fat” when it’s actually “high Omega-6”, and even more dangerous when the media makes the same mistake.
So, throw your corn oil away, always dig into the source before believing these kinds of articles, and pop some of those fish oil pills.