One of the major changes in diet that I didn't mention in the last post was the rise of industrial liquid vegetable oils over the course of the 20th century. In the U.S. in 1900, the primary cooking fats were lard, beef tallow and butter. The following data only include cooking fats and spreads, because the USDA does not track the fats that naturally occur in milk and meat (source):
Animal fat is off the hook. This is the type of information that makes mainstream nutrition advice ring hollow. Let's see what happened to industrial vegetable oils in the early 1900s:
I do believe we're getting warmer. Now let's consider the composition of traditional American animal fats and industrial vegetable oils:
It's not hard to see that the two classes of fats (animal and industrial vegetable) are quite different. Animal fats are more saturated (blue). However, the biggest difference is that industrial vegetable oils contain a massive amount of omega-6 (yellow), far more than animal fats. If you accept that humans evolved eating primarily animal fats, which is well supported by the archaeological and anthropological literature, then you can begin to see the nature of the problem.Omega-6 and omega-3 fats are polyunsaturated fatty acids that are precursors to a very important class of signaling molecules called eicosanoids, which have a hand in virtually every bodily process. Omega-6 and omega-3 fats compete with one another for the enzymes (desaturases and elongases) that convert them into eicosanoid precursors. Omega-6-derived eicosanoids and omega-3-derived eicosanoids have different functions. Therefore, the balance of omega-6 to omega-3 fats in the diet influences the function of the body on virtually every level. Omega-6 eicosanoids tend to be more inflammatory, although the eicosanoid system is extraordinarily complex and poorly understood.
What's better understood is the fact that our current omega-6 consumption is well outside of our ecological niche. In other words, we evolved in an environment that did not provide large amounts of omega-6 all year round. Industrial vegetable oils are a product of food processing techniques that have been widespread for about 100 years, not enough time for even the slightest genetic adaptation. Our current level of omega-6 intake, and our current balance between omega-6 and omega-3, are therefore unnatural.
The ideal ratio is probably very roughly 2:1 omega-6:omega-3. Leaf lard is 6.8, beef tallow is 2.4, good quality butter is 1.4, corn oil is 45, cottonseed oil is 260. It's clear that a large qualitative change in our fat consumption occurred over the course of the 20th century. I believe this was a major factor in the rise of heart attacks from an obscure condition to the primary cause of death. I'll be reviewing the data that convinced me in the next few posts.
The Coronary Heart Disease Epidemic
The Coronary Heart Disease Epidemic: Possible Culprits Part I
The Omega Ratio
A Practical Approach to Omega Fats
Polyunsaturated Fat Intake: Effects on the Heart and Brain
Polyunsaturated Fat Intake: What About Humans?
Vegetable Oil and Homicide