Dietary-fat recommendations for heart health are more specific now then ever, breaking down different types of polyunsaturated and saturated fats, and recommending whole foods that confer benefits above and beyond their fatty-acid profile. For a period of time, all fats were demonized as the cause of obesity and heart disease. But times have changed, according to Karen Lapsley, Ph.D., chief scientific officer, Almond Board of California, Modesto. “Research and public-policy opinions related to fat in the diet have changed incredibly in the past years,” she says. “There is an increased interest in the quality of dietary lipids as a major determinant of long-term health and well-being. With evolving nutrition science, we now talk about healthy food with a high fat quality—which must be differentiated from talking simply about foods of high or low fat quantity.”
In the 1950s, people were advised to decrease their total fat intake. For approximately 40 years thereafter, the recommendations were to decrease consumption of total fat, saturated fat and cholesterol, while increasing intake of foods rich in monounsaturated and polyunsaturated fats.
In the past 15 years, however, the focus has shifted from total fat to “good fats” and “bad fats.” By the mid-1990s, mounting scientific evidence of the negative health effects from consumption of manmade trans fatty acids parlayed into an onslaught of public-health messages, labeling requirements and changes in food manufacturing. On the “good fat” side, the omega 3s eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) reign (Journal of Nutrition, 1998; 128:449S-452S).
Harmful fats
For several years, health authorities were so busy demonizing all foods high in saturated fat that they overlooked the negative health effects of manmade trans fatty acids hiding in seemingly healthy vegetable-oil products. However, more-recent research indicates that not all saturated fatty acids are harmful for the heart.
There are several factors that can influence the atherogenic potential of specific saturated fatty acids, including chain length, fats eaten concurrently, overall diet, carbohydrate intake, and the person’s state of health. Studies show that stearic acid has a neutral effect on HDL and lowers LDL in comparison to unsaturated fatty acids (American Journal of Clinical Nutrition, 2010; 91:46-63). In addition, replacing carbohydrate with fat (including saturated fat) will decrease triglycerides and increase HDL cholesterol (American Journal of Clinical Nutrition, 1995; 61:1,368S-1,373S). And, making matters somewhat more complex, the importance of total blood cholesterol, and therefore factors that alter blood cholesterol, as a risk factor for heart disease has been questioned following the discovery that statin drugs work, in part, independently of cholesterol reduction (Alternative Medicine Reviews, 2007; 12:228-45). Consequently, some scientists have diverging opinions on saturated fat and heart health, especially considering the specific population consuming the fat (Archives of Internal Medicine, 2009; 169:659-669).
Although research is still examining relationships between saturated-fatty-acid intake and cardiovascular-disease risk factors (especially in those on low- or very-low-carbohydrate diets), the consensus is in on manmade trans fatty acids from partially hydrogenated oils: They decrease HDL and increase LDL, triglycerides, insulin resistance and risk of cardiovascular disease (Circulation, 2007; 115:1,858-1,865; American Journal of Public Health, 1995; 85:411–412; New England Journal of Medicine, 2006; 354:1,601-1,613). Despite the fact that manmade trans fatty acids are bad for the heart, studies indicate that the naturally occurring trans fatty acid vaccenic acid, found in ruminant fats and converted into conjugated linoleic acid (CLA) in the body, has no affect on cardiovascular disease and may in fact have some health benefits (Applied Physiology, Nutrition and Metabolism, 2009; 34(5):979-991).
