Trans-palmitoleic acid is found in the fat of ruminant animals such as cows, sheep, and goats. (Larry Crowe/Associated Press)

A natural fatty acid found in whole-fat dairy products may lower the risk of Type 2 diabetes, U.S. scientists have found.

Studies on populations show that diets rich in dairy foods such as milk, cheese, yogurt and butter are linked to lower risk of Type 2 diabetes. Animal studies also suggest naturally occurring palmitoleic acid helps protect against insulin resistance and diabetes.

The reasons for the effect are unknown. To find out more about the fatty acid and its potential health benefits, researchers at the Harvard School of Public Health analyzed data from more than 3,736 American seniors who have been followed for 20 years as part of a study on risk factors for cardiovascular diseases.

Unlike industrially produced trans fats found in partially hydrogenated vegetable oils, which have been linked to higher risk of heart disease, trans-palmitoleic acid is found mainly in naturally-occurring dairy and meat. Previous studies have not linked this type of trans fat to higher risk of heart disease.

In the study, participants who said they consumed more whole-fat dairy products had higher levels of trans-palmitoleate in their blood three years later, the study's lead investigator, Dariush Mozaffarian, an epidemiology professor at Harvard and his co-authors report in the December issue of the Annals of Internal Medicine.

People with the highest levels of the fatty acid circulating in their blood had about two-thirds the risk of developing Type 2 diabetes than those with the lowest levels, the researchers found.

'Strong protective effect'

"This is an extremely strong protective effect, stronger than other things we know can be beneficial against diabetes," said Gökhan Hotamisligil, the study's senior author and chair of the department of genetics and complex diseases at Harvard School of Public Health.

"The next step is to move forward with an intervention trial to see if there is therapeutic value in people," he added in a statement.

The researchers found people with higher levels of trans-palmitoleic acid also tended to show:

• Slightly less fat on their bodies.
• Higher "good" cholesterol levels and lower overall cholesterol levels.
• Lower levels of C-reactive protein, a marker of inflammation.
• Evidence of lower levels of insulin resistance.

Insulin resistance occurs when the body produces too little of the hormone insulin and fails to effectively regulate the metabolism of fats, proteins and sugars. The condition can lead to Type 2 diabetes.

In the study, participants were asked only once about the foods they usually eat, but dietary habits may change over time and blood levels may no longer reflect that, the researchers noted in listing the limitations of the study.

As well, this type of study cannot say whether it was in fact trans-palmitoleate behind the beneficial health effects or some other unknown factor. For example, trans-palmitoleate could be a marker for some other protective element in dairy foods.

It is therefore too soon to tell how many servings of dairy might be beneficial or to take many dietary recommendations based on the findings, the researchers said.

Dr. Sue Kirkman, senior vice-president of medical affairs and community information for the American Diabetes Association, agreed that it's too soon to change dietary guidelines.

The findings do suggest "that things may be more complicated than we might simplistically think. It looks like we can't say all trans fats are bad, as this one was associated with decreases in diabetes, insulin resistance and C-reactive protein levels," Kirkman told Health Day.

The study was funded by the U.S. National Heart, Lung, and Blood Institute, the U.S. National Institute of Diabetes and Digestive and Kidney Diseases, the National Institutes of Health Office of Dietary Supplements and National Institute of Neurological Disorders and Stroke.