Public health guidelines, such as the Dietary Guidelines for Americans, have long emphasized reducing dietary fat intake, but nutritionists and other health scientists now have more recent evidence that not all fats have adverse effects. Dietary fats differ with regard to their effects on health and risk for chronic diseases, particularly in regard to effects on risk for heart disease.
Indeed, some nutrition experts now believe that certain types of dietary fat may even reduce cardiovascular risk. Some dietary fats may lower fats in the blood called triglycerides. They may also increase levels of HDL, or what is known as the “good” cholesterol, and reduce LDL-cholesterol, or the less healthy type of cholesterol, thus improving the HDL to total cholesterol ratio.
Also, many diet plans that do not strictly limit the total amount of dietary fat a person consumes have been associated with better diet satisfaction, weight loss, and preservation of muscle mass.
As a research professor in the field of nutrition and dietetics, I am convinced that findings from our work, along with other published current evidence, show that the concept that dietary fat is “toxic” is very much outdated and misguided.
Although there is conclusive evidence that one type of fat, trans fat, has no place in a healthy diet, I believe that consumers should start to learn how to balance the other types of fats in the diet.
A balancing act
While not all fats are alike, they do share some things in common. They provide energy with approximately nine calories per each gram of fat, they are all broken down during digestion by enzymes in the gastrointestinal tract, and they are well absorbed as fatty acids, or chains of hydrogen and carbon.
But these carbon chains vary in length and their degree of saturation. As a result, dietary fats vary in their effects on the body.
In some instances, the carbon molecules bind to other carbon molecules. In others, they bind to hydrogen molecules. You likely have heard names for these two types of fats – unsaturated and saturated. Unsaturated fats are those in which carbon molecules bind to other carbon molecules. Saturated fats are those in which carbon molecules bind to hydrogen molecules. Within the two broad types of fat, there are differences still.
Among the unsaturated fats, there are those that are mono-unsaturated, or those that have one unsaturated carbon bond, which are found in olive oil and certain kinds of nuts, and there are those that are poly-unsaturated and are found in such foods as walnuts, plant oils, salmon and sardines.
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We also have learned that different kinds of saturated fats affect the body in different ways. For example, the 12-carbon lauric acid, 14-carbon myristic acid, 16-carbon palmitic acid and 18-carbon stearic acid are all saturated fats. But, stearic acid does not increase LDL-cholesterol levels like the other saturated fats.
While these differences are not new, the understanding of their effects is new, mostly due to findings from more recent studies like my own.
Thus, the amount of total fat in the diet no longer is the sole measure of the health effects of dietary fat. It’s also about the type of fatty acid, how long the carbon chain is, and whether the fat is saturated, mono-unsaturated or poly-unsaturated.
The link to heart health
The scientific discourse about the potentially toxic role of dietary fat and cholesterol on human health started in the late 1950s and early 1960s, when scientists discovered how to analyze fats in the lab. They also discovered the link between dietary fat intake, serum levels of total and LDL-cholesterol, and risk for cardiovascular diseases in animals.