Conventional wisdom holds that people should follow a healthy diet and get regular exercise to help control their cholesterol and triglycerides, another type of harmful blood fat. But there has actually been little research into how well older adults' cholesterol and triglyceride levels respond to diet changes.

In the new study, researchers looked at the effects of dietary-fat changes among 900 Australian adults age 49 and older who were followed for 10 years. At the outset, 5 percent were taking a cholesterol-lowering medication, usually a statin; a decade later, one-quarter were using drugs to control their cholesterol.

At the same time, "good" HDL cholesterol levels inched upward when study participants started eating more fish and omega-3 fatty acids -- healthy, unsaturated fats found mainly in oily fish like salmon and mackerel. People who boosted their omega-3 from food also showed declining triglyceride levels.