In the last 2 1/2 years, since adopting a lower carb way of eating, I've done a lot of reading about diet and inflammation and heart disease. Many articles in the medical literature call out inflammation as the key factor that leads to heart disease. I don't think that this has been definitively proven but it helps explain many contradictions.
If high levels of low density lippoproteins (LDL) cholesterol in the blood cause athlerosclerosis and lead to heart disease-caused death, then why don't all people with high LDL cholesterol die of heart disease? Conversely, if high LDL is the absolute cause of heart disease, then why do people with normal LDL levels still die from heart disease (see Tim Russert's case)?
There must be some other yet to be understood factors involved in the process and inflammation may well answer some of these questions.
As to what may be causing inflammation, that is the great unanswered question. Some nutrition experts point to the imbalance of omega 6 fatty acids to omega 3 fatty acids in our blood. Omega 6 polyunsaturated fatty acids (from vegetable oils, grains, legumes, and nuts) and omega 3 polyunsaturated fatty acids (fish and flaxseed) over our human evolution have been found to be consumed in a 1:1 ratio.
During the last hundred years or so that ratio has drastically changed. Here's what nutrition writer Chris Kresser has to say on this topic:
Vegetable oil consumption rose dramatically between the beginning and end of the 20th century, and this had an entirely predictable effect on the ratio of omega-6 to omega-3 fats in the American diet. Between 1935 and 1939, the ratio of n-6 to n-3 fatty acids was reported to be 8.4:1. From 1935 to 1985, this ratio increased to 10.3:1 (a 23% increase). Other calculations put the ratio as high as 12.4:1 in 1985. Today, estimates of the ratio range from an average of 10:1 to 20:1, with a ratio as high as 25:1 in some individuals.
In fact, Americans now get almost 20% of their calories from a single food source – soybean oil – with almost 9% of all calories from the omega-6 fat linoleic acid (LA) alone! (PDF)
This reveals that our average intake of n-6 fatty acids is between 10 and 25 times higher than evolutionary norms. The consequences of this dramatic shift cannot be overestimated.
Chris goes on to write this in the same article:
In plain english, what this means is that the more omega-3 fat you eat, the less omega-6 will be available to the tissues to produce inflammation. Omega-6 is pro-inflammatory, while omega-3 is neutral. A diet with a lot of omega-6 and not much omega-3 will increase inflammation. A diet of a lot of omega-3 and not much omega-6 will reduce inflammation.
This seems like a credible explanation to me, even though science has not yet made this conclusion. Due to our limited lifespan, sometimes we can't wait for the definitive science and instead must act with our best instincts.