Dairy Fat May Lower Diabetes Risk
New Research Suggests That a Fat Found Primarily in Dairy Foods May Lower Diabetes Risk
By Salynn Boyles
WebMD Health News
Reviewed by Laura J. Martin, MD
milk pouring in glass

Dec. 20, 2010 -- Experts recommend avoiding high-fat dairy products to lower diabetes risk, but a new study suggests this advice may be wrong.

Researchers at the Harvard School of Public Health say they have identified a substance found primarily in dairy fat that appears to lower the risk of type 2 diabetes.

Known as trans-palmitoleic acid, it is present in the fat of ruminant animals such as cows, sheep, and goats.

In the Harvard study, people with the highest levels of the fatty acid in their blood had a threefold lower risk of developing diabetes over time than people with the lowest levels.

They also had healthier HDL, or good, cholesterol levels, lower body fat, and less insulin resistance.

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Dairy Fat and Diabetes

But it is too soon to switch from skimmed milk and low-fat yogurt to higher-fat versions.

The findings must be confirmed, researchers say, and it is not quite clear if trans-palmitoleic acid or a related compound was protective.

The Harvard study was funded by grants from the National Institutes of Health. It appears in the Dec. 21 issue of the Annals of Internal Medicine.

“If nothing else, I think we have confirmed that there is something in dairy that reduces the risk of diabetes,” lead researcher Dariush Mozaffarian, MD, tells WebMD. “Either it is this fatty acid or something associated with it that we have not identified. It would be highly implausible that the relationship we saw is due to something unrelated to dairy.”

The study included 3,736 participants in the National Heart, Lung, and Blood Institute (NHLBI)-run Cardiovascular Health Study.

Throughout the two-decade study, researchers measured metabolic markers of diabetes risk, including circulating blood fatty acid levels.

Higher blood levels of trans-palmitoleic acid at study entry were associated with better cholesterol, less insulin resistance, and less overall inflammation, even after researchers adjusted for other heart disease and diabetes risk factors.

Over 20 years of follow-up, participants with the highest circulating levels of the fatty acid had about a 60% lower risk of developing diabetes than people with the lowest levels.

The finding could explain earlier research suggesting that people who eat more dairy products have a lower risk of developing type 2 diabetes, Mozaffarian says.
Advice to Limit Dairy Fat Still Stands

In a news release, study co-author Gokhan Hotamisligil, MD, PhD, notes that the next step will be to isolate the fatty acid to test its ability to lower diabetes risk in clinical trials.

“This is an extremely strong protective effect, stronger than other things we know can be beneficial against diabetes,” Hotamisligil says in the release.

The American Diabetes Association (ADA) makes a clear distinction between healthy fats and unhealthy fats, and, not surprisingly, dairy fat falls into the latter category.

On its web site, the ADA recommends limiting saturated and trans fats, and the group identifies full-fat cheese, ice cream, butter, whole milk, and 2% milk as foods to be limited by people with diabetes to lower their risk for heart disease.

“Instead of one cheese stick for an afternoon snack, have 12 almonds,” the ADA advises in its web site. “The calories are about the same, but you will have improved your heart health with that single change.”

Nutritionist Marion Franz, MS, RD, who serves on the ADA nutrition task force, calls the Harvard findings "interesting early research" but says the recommendation to limit dairy fat is still a good one.

“This is an observational study that suggests a direction research should go in,” she says. “But we have seen these studies before suggesting that a single micronutrient or food is protective and little has come of it.”

She says the link between eating saturated fats and heart disease is well established. Several studies have also linked saturated and total fat consumption to insulin resistance and diabetes.

“It is true that some studies have shown benefits for dairy foods in diabetes, but other studies show the same thing for the Mediterranean diet, which is high in fruits, vegetables, and nuts but low in dairy,” she says.