Fat.

Like it or not, we all need to eat it to stay healthy. But it turns out that the type of fat makes all the difference—saturated, monounsaturated, polyunsaturated, trans fat—and probably is more important than how much total fat we eat, and it has a big effect on our risk of cardiovascular disease (CVD), a group of diseases that is the top killer in America. Though knowing which fats are healthiest is so important, determining which ones are has been protracted and controversial. For an explanation of what fatty acids are and what the terms saturated, monounsaturated, polyunsaturated, omega-3, and omega-6 mean, follow this link to the University of Utah.

It turns out that common recommendations for fat consumption may be unfounded—saturated fats may not be so bad after all. It appears that the Mediterranean diet, which includes a significant amount of fat, is one of the best diets to reduce risk of CVD. In general, combining the findings of many recent studies on fat and CVD, it seems good advice for someone following a typical Western diet to significantly increase omega-3 consumption, slightly increase omega-6 consumption, slightly decrease saturated fat consumption, and greatly decrease consumption of refined carbohydrates, especially white bread and sugar.

The Academy of Nutrition and Dietetics recommends that people limit saturated (SFA) and trans fatty acid (TFA) intake and focus on mono- (MUFA) and polyunsaturated (PUFA) fatty acids to reduce the risk of cardiovascular disease (CVD), which is in line with common knowledge. However, the authors of a 2013 article entitled “The role of dietary fats for preventing cardiovascular disease. A review,” point out that recent studies have shown that SFAs do not unequivocally increase one’s risk of CVD.

Whether or not SFA intake correlates with CVD risk seems to depend on what people eat more of to replace the lost SFAs. Several studies cited by the aforementioned article, including one I have also read, “Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease,” have shown that when people replace SFAs with PUFAs, their risk of CVD decreases, but when they replace SFAs with refined carbohydrates, their risk of CVD actually increases as they eat less SFAs, which is contrary to common knowledge. The effects of replacing SFAs with MUFAs are more ambiguous.

However, it is unclear whether it is better to replace SFAs with omega-6 fatty acids or not. Both omega-6 and omega-3 fatty acids are polyunsaturated, and they have been shown, respectively, to promote and mitigate inflammation, and to increase and decrease CVD risk. There is no officially recommended ratio of omega-6s to omega-3s, but the Mediterranean diet provides a ratio of about 2:1, while typical Western diets have ratios around 15:1, which increases CVD risk. Replacing SFAs with omega-6s has been shown in some studies to reduce CVD risk but to increase CVD risk in others.

Oils are pure liquid fats, but they differ markedly in composition; data can be found in the first article. Of two common oils with the most omega-3s, flaxseed oil is over 50% omega-3s and 20% omega-6s by mass, while rapeseed oil—which is actually cheaper than olive oil—is about 10% omega-3s and 20% omega-6s. Olive oil has almost no omega-3s, but it is only about 10% omega-6s, so eating it with either of the other two oils would still allow a low omega-6/omega-3 ratio.

In general, those following a Western diet should eat more omega-3s and a little more omega-6s, eat a little less saturated fat, and eat many fewer refined carbohydrates. The studies have shown that the Mediterranean diet seems to be very protective against CVD, so the more our diets resemble it, the more likely it seems that we can reduce our CVD risk and live healthier, longer lives.