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our work, along with other published current evidence, show that the concept that dietary fat is “toxic” is very much outdated and misguided.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, it’s important 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 still more different sorts.
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.
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
In the mid-1980s, advice to consume a low-fat diet became a strategy for weight control. Evidence from the landmark Framingham Heart Study uncovered that obesity increased risk for heart disease, and national data showed that the entire population was getting heavier.
Americans responded with a substantial reduction in the percentage of calories consumed as fat. But humans have a biological preference for the taste of fat. And with fat off the table, millions increased their consumption of dietary carbohydrates to compensate for the loss in flavor and appeal of foods. As a result, there has been a substantial increase in the waistlines of Americans.
An Alternative Approach
Given the mixed scientific evidence on fat, and the diverse roles of dietary fatty acids in health and disease, about four years ago I designed a diet that is moderately high in fat, but the types of fat are proportionally balanced, that is, one-third of total fat comes from saturated fats; one-third comes from monounsaturated fats; and one-third comes from polyunsaturated fats.
Based on this balanced moderately high fat diet approach, my research team developed a 14-day cycle of menus comprised of three meals and two snacks per day that increases intake of foods high in the 18-carbon monounsaturated fat, oleic acid, and the 18-carbon and longer chain polyunsaturated fats (more commonly known as omega-3 and omega-6 fatty acids). To do this, we replaced high simple carbohydrate snacks with nuts, we replaced croutons in salads with avocado slices, and we used salad dressings high in safflower oil, canola oil and olive oil.
We have been studying the effects of this balanced moderately high fat diet in adults who are overweight or obese. In a study with 144 women over a period lasting 16 weeks, we found that study participants had significant reductions in abdominal fat and waist circumference; a 6 percent improvement in blood pressure; reduced blood levels of markers of inflammation; and overall a 6 percent reduction in their five- and 10-year cardiovascular risk.
Study participants reported that they found our diet to be highly palatable, satisfying and economically feasible to adhere to. The firm adherence to our balanced moderately high fat diet in the four-month study was reflected by significant changes in participants’ plasma fatty acid profiles (the array of saturated and unsaturated fats in the blood) that reflected the fatty acid composition of the diet menus.
There are limited studies on the strategy of balancing the types of dietary fat. While current scientific consensus is that extremes of dietary fat intake, too high or too low, are unhealthy, I believe that a paradigm shift focusing on the types of dietary fats consumed may offer the opportunity to modify our cardiometabolic risk factors without requiring major changes in the amount of fat or calories we consume.