A cornerstone of dietary advice has long been to replace saturated fat with polyunsaturated fat to reduce risk of heart disease. This is advice that has been challenged in the past few years, however. Health writers and some nutrition experts have questioned whether saturated fat is to blame for heart disease or whether other dietary components are the culprits. Suddenly, bacon and steak have become the new health foods.
Two new studies, however, reaffirm the wisdom of choosing unsaturated over saturated fats. One was an analysis of 13 prospective epidemiologic studies involving 300,000 subjects (1). These were all studies in which healthy individuals provided information about their dietary intakes at the beginning of the study and then were followed for many years to see how diets correlated with disease outcomes. The researchers, including several from Harvard University, divided the subjects into five groups according to the amount of polyunsaturated fat they consumed. Those in the group with the highest intakes were 15% less likely to have a heart attack and 21% less likely to die from coronary heart disease.
According to the results, a person consuming about 1,800 calories per day could reduce his or her risk of a heart attack by 9% by replacing the amount of saturated fat found in a typical fast food hamburger with the amount of polyunsaturated fat provided by about two-thirds of a cup of soynuts. The protective effect held even after the researchers adjusted for other heart disease risk factors and for other dietary factors like fiber and omega-3 fats. Replacing carbohydrate with polyunsaturated fats also provided benefits.
In the second study, researchers looked directly at blood levels of polyunsaturated fat and their relationship to heart disease risk (2). Blood levels can be a better indicator of dietary intake since people often have trouble recalling what they eat. This study included 3,000 participants who were all at least 65 years old. The key finding was that a higher blood level of the main type of polyunsaturated fat was associated with 13% reduction in the risk of dying from all causes.
These two studies strongly emphasis the health benefits of foods that are low in saturated fat and high in polyunsaturated fat. Soyfoods can be part of a heart-healthy diet because they are low in saturated fat and high in polyunsaturated fat. Cooking with small amounts of soy oil can also improve the fatty acid profile of diets.
1) Farvid MS, Ding M, Pan A, et al. Dietary linoleic acid and risk of coronary heart disease: A systematic review and meta-analysis of prospective cohort studies. Circulation 2014.
2) Wu JH, Lemaitre RN, King IB, et al. Circulating omega-6 polyunsaturated fatty acids and total and cause-specific mortality: The Cardiovascular Health Study. Circulation. (2014).