By Stacy Kennedy, M.P.H., R.D., L.D.N., C.N.S.D.
Americans have been working hard to go "fat-free" during the last few decades, believing it would lead to better health, but we are slowly learning that fat is not our enemy. In fact, after two decades of research, science is now able to step in and comment on the true effects of eating certain types of fats. In particular, omega-3 fats have proven to be an essential part of a healthy diet and an important aid in preventing sickness and disease.
Fat's negative social stigma was broadcast from our government and media with persistence. While the total amount of fat in people's diets decreased from 40% in 1962 to 34% in 2000, health actually has worsened. In fact, Americans are fatter today than ever before, with numbers reaching epidemic proportions in both adults and children.
However, despite staggering obesity rates, Americans have simply misinterpreted the quality of fats.
Fats play many important roles in the body and are the foundation of key compounds such as hormones. Studies have shown that eating fat actually can promote weight loss in a calorie-controlled environment. In other words, eating a higher percentage of fat is healthy as long as you're not eating too many calories overall. Researchers from the Harvard School of Public Health recently demonstrated that the total amount of fat in the diet does not increase the risk of many types of cancers and heart disease, as long as weight and total calories are appropriate. Instead, their findings suggest that the type of fat may play a more significant role in the development of heart disease, diabetes and certain types of cancers.
Omega-3 fat, a polyunsaturated fat found in both animal and plant sources, fits the profile of a healthy fat. Omega-3 fats are considered essential, meaning we have to eat them because our body cannot produce them on its own. They help to drive normal brain and nervous-system development and function, immune function, blood flow, heart rhythm and healthy skin. The most active omega-3 fatty acids are known as EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). These can be directly obtained from marine animals and algae. Another important but slightly less active omega-3 fatty acid is alpha-linolenic acid (ALA), found in flaxseeds, canola oil and walnuts.
Fish and plants rich in omega-3 fats may help prevent heart attacks, sudden cardiac death and certain types of stroke by decreasing blood clots, erratic heart rhythm, inflammation and triglycerides, while raising HDL, or "good" cholesterol. Scientists also are excited about the anti-inflammatory properties of omega-3 fats that might lead to treatments for cancer and autoimmune disorders such as rheumatoid arthritis and lupus.
Right now, the best way to get omega-3 is from food sources. Eating 4 ounces of omega-3-rich fish two to three times a week is sufficient and safe. Omega-3-rich fish have been shown to have low or negligible mercury and other heavy metal content.
Stacy Kennedy, M.P.H., R.D., L.D.N., C.N.S.D., is senior clinical dietician at Dana-Farber Cancer Care/Brigham and Women's Hospital. She completed her dietetic internship at Massachusetts General Hospital and received her Master of Public Health in Nutrition from the University of North Carolina.