Fats are an essential part of your diet. Your body uses fats for energy, vitamin absorption, insulation, and a number of other necessary functions. But not all fats are created equal, and eating too much of the wrong type of fat can increase your risk of cardiovascular disease. The U.S. Department of Agriculture’s 2005 Dietary Guidelines for Americans recommend keeping your intake of fat between 20% and 35% of your total daily caloric intake, limiting foods that are high in saturated and trans fatty acids and consuming mostly polyunsaturated and monounsaturated fats, such as those found in fish, nuts, and vegetable oils.

So what is more important: reducing your fat intake or substituting the “bad” fats with the “good” fats? Surprisingly, there are few randomized, prospective studies (the gold standard in research) on this topic. There is some experimental evidence suggesting that polyunsaturated and monounsaturated fats may reduce inflammation and clotting in blood vessels, theoretically leading to a decreased risk of cardiovascular disease.

A new study in the January 24, 2005 issue of the Archives of Internal Medicine looked at the diets of more than 1,500 middle-aged men and found that those who consumed the most polyunsaturated fatty acids were significantly less likely to die of cardiovascular disease than those who consumed the least. Total fat intake, on the other hand, did not affect the risk of dying from cardiovascular disease.

About the Study

Researchers used data from the Kuopio Ischaemic Heart Disease Risk Factor (KIHD) Study, a prospective study of 2,682 Finnish men ages 42–60 when the study began in 1984–1989. The present study looked at the 1,551 participants who did not have a history of cardiovascular disease, diabetes, or cancer when the study began, and who had complete records of their dietary intake.

The researchers determined the men's fat intake using four-day food diaries.  Fat intake was broken down into cholesterol, saturated fatty acids (SAFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA). The researchers also measured intakes of two specific types of PUFA: linoleic acid (an omega-6 fatty acid) and alpha-linolenic acid (an omega-3 fatty acid). Omega-6 and omega-3 fatty acids are "essential" PUFA, which means your body cannot produce them on its own—you must get them in your diet.

The researchers also looked at the presence of fatty acids in the participants’ blood. They followed the men for an average of 15 years, keeping track of deaths from cardiovascular disease and all other causes.

The Findings

During the 15-year follow-up period, 78 men died of cardiovascular disease and 225 died of other causes.

Intake of total fat, MUFA, and cholesterol did not affect the men’s risk of dying from cardiovascular disease.

The men with PUFA intake in the upper third and, more specifically, those with linoleic acid intake in the upper third, were about 60% less likely to die from cardiovascular disease than men with intakes in the lower third. In addition, the men whose linoleic acid intake was in the upper third were 33% less likely to die from non-cardiovascular causes than the men with linoleic acid intakes in the lower third.

The men with the highest PUFA/SAFA ratio were 54% and 29% less likely to die of cardiovascular disease and all other causes, respectively.

The levels of fatty acids detected in the participants’ blood samples generally mirrored those calculated from the food diaries.

How Does This Affect You?

These findings suggest that, for middle-aged men, the quality of dietary fat may have more of an impact on cardiovascular risk than the quantity. Compared with previous research on the topic, this study was especially compelling, since it included a large number of participants over a long period of time, and dietary fat assessment was conducted with both food diaries and blood sample analyses.

This study does not mean people should begin consuming large quantities of “good” fats and stop worrying about how much total fat they consume. Compared to carbohydrates and protein, fat has more than double the amount of calories per gram, which means a diet high in fat is likely to be high in calories. High-calorie diets can lead to obesity , which is a major health problem that increases the risks of diabetes , heart disease , stroke , certain cancers, and a number of other conditions.

These findings do, however, suggest that substituting most of the saturated fat (e.g., whole milk, butter, cheese) in your diet with PUFA may help reduce your risk of dying from cardiovascular disease. These “good” fats are found in safflower, sunflower, corn, sesame, soybean, and other vegetable oils that stay liquid at room temperature.