What is the problem and what is known about it so far?

Fatty acids are found in oils and other fats in our diets. In addition, many are made by our bodies. High and low levels of various fatty acids in the blood have been associated with both good and bad effects on health. Whether a single fatty acid has good or bad health effects may depend on its source (whether it was produced by the body or consumed in fats from meat or dairy products).

Why did the researchers do this particular study?

Previous studies in animals have suggested that a particular fatty acid (cis-palmitoleate) may have beneficial health effects. The researchers wanted to see whether blood levels of trans-palmitoleate, a closely related fatty acid derived predominantly from whole-fat dairy products, might be associated with beneficial health effects in humans.

Who was studied?

3736 men and women aged 65 years or older who agreed to have repeated interviews and examinations over many years to identify risk factors for various diseases.

How was the study done?

The researchers first asked participants to complete a questionnaire about the foods they usually ate and about other factors that might affect their health. Three years later, blood samples were taken to measure fatty acid levels (including trans-palmitoleate). Participants were then evaluated each year to determine whether health problems had occurred.

What did the researchers find?

Participants who said they ate more whole-fat dairy products had higher levels of trans-palmitoleate in their blood 3 years later. Over the following years, participants who had higher levels of trans-palmitoleate in their blood had better levels of some chemicals associated with good health (such as certain types of cholesterol) and were less likely to develop diabetes.

What were the limitations of the study?

Participants were asked only once about the foods they usually eat, and dietary habits may change over time. The blood levels of trans-palmitoleate measured several years later may have no longer related to the types of foods the participants originally reported eating. In addition, this kind of study cannot tell us whether trans-palmitoleate or some other unidentified factor was the cause of the good health effects seen.

What are the implications of the study?

More research is needed to see whether trans-palmitoleate from dairy fat might be useful in preventing diabetes.