Dairy Saturated Fats Lower Type 2 Diabetes Risk

Kathleen Louden

August 14, 2014

The odds of incident type 2 diabetes is lower in people who have high plasma levels of odd-chain saturated fatty acids that come primarily from dairy fats, compared with people who did not have these biomarkers, a large, prospective multicenter study finds.

In contrast, even-chain saturated fatty acids, such as those that come from consuming alcohol, soft drinks, or margarine, were associated with a greater likelihood of diabetes in the study, published online August 6 in Lancet Diabetes & Endocrinology. These fatty acids include palmitic acid, the most common saturated fatty acid in the US diet.

The findings suggest that saturated fatty acids are not homogeneous in their effects and "emphasize the importance of the recognition of subtypes of these fatty acids," say Nita Forouhi, FFPHM, from the Medical Research Council (MRC) Epidemiology Unit at the University of Cambridge, United Kingdom, and colleagues in their paper.

"The message from this study is that saturated fatty acids are not only different but have opposite relationships with diabetes risk," Dariush Mozaffarian, MD, DrPH, dean of the Friedman School of Nutrition Science and Policy at Tufts University, in Boston, Massachusetts, told Medscape Medical News.

Dr. Mozaffarian is the author of a commentary that accompanies the research. "These results add to growing evidence that dairy fat might reduce insulin resistance and type 2 diabetes; benefits that might be greatest for cheese and yogurt," he writes.

Diabetes Risk Varies by Fatty-Acid Carbon Chain

In their paper, Dr. Forouhi and colleagues explain that saturated fatty acids are generally thought to have a detrimental impact on health, but little evidence exists to support the adverse effects of high saturated fatty-acid intake on the risk for type 2 diabetes.

In this longitudinal case-cohort analysis, they aimed to investigate the prospective associations between objectively measured levels of 9 saturated fatty acids in the plasma and incident type 2 diabetes in participants from the European Prospective Investigation into Cancer and Nutrition (EPIC)-InterAct study.

They identified 12,132 verified cases of type 2 diabetes and 15,919 subcohort participants (including an "overlap" of 755 incident cases of type 2 diabetes, a feature of case-cohort studies). They used gas chromatography to measure the distribution of fatty acids in plasma phospholipids.

The investigators found that saturated fatty acids with an odd number of carbon atoms in their chain—15:0 and 17:0—were associated with a lower risk of type 2 diabetes, whereas even-chain saturated fatty acids—14:0, 16:0, and 18:0—were associated with a higher risk.

Longer-chain saturated fatty acids—20:0, 22:0, 23:0, and 24:0—also were found to be inversely associated with incident type 2 diabetes.

These associations held true for each saturated fatty acid individually and when combined by carbon-chain group (even, odd, or longer).

Hazard Ratio for Type 2 Diabetes by Saturated Fatty-Acid Carbon-Chain Group

Saturated fatty-acid carbon-chain group Fatty acids measured Hazard ratio 95% Confidence Interval
Even chain Myristic, palmitic, and stearic acids 1.43 1.29–1.58
Odd chain Pentadecanoic and heptadecanoic acids 0.70 0.66–0.74
Longer chain Arachidic, behenic, tricosanoic, and lignoceric acids 0.70 0.59–0.84

The presence of odd-chain saturated fatty acids are well-established markers for eating dairy fat, according to the authors. The other saturated fatty acids can be exogenous or endogenous.

The researchers found that the fatty-acid groups correlated with types of self-reported food intake. Specifically, even-chain saturated fatty acids were positively associated with alcohol, soft drinks, margarine, and potatoes and were negatively associated with fruits and vegetables, olive oil, and vegetable oil.

Odd-chain saturated fatty acids demonstrated positive associations with dairy products, nuts and seeds, fruits and vegetables, and cakes and cookies but negative associations with red and processed meat, alcohol, soft drinks, and margarine.

"An improved understanding of differences in sources of individual saturated fatty acids from dietary intake vs endogenous metabolism is needed," they conclude.

Dr. Mozaffarian said he does not believe that clinical practice should change because of the findings from any single study, despite the many strengths of this new research.

Because fatty acids are complicated, he said, "We need to have many more large studies and also trials to assess the effects over time of different saturated-fat–containing foods on diabetes risk."

New Dietary Guidelines Needed?

But based on a large body of existing scientific evidence, Dr. Mozaffarian called for US dietary guidelines to move away from "overly simplistic" groupings, such as total saturated fat, and toward food-based guidelines that consider prospective evidence for effects on clinical end points.

In his commentary, he suggests that the guidelines might consider "the complex nutrients and preparation methods of different dairy foods."

A spokeswoman for the Academy of Nutrition and Dietetics (formerly the American Dietetic Association) disagrees, however.

 
This study gives us permission to be a little indulgent with a full-fat dairy item now and then.
 

Angela Ginn, RDN, LDN, a senior diabetes educator from the University of Maryland Center for Diabetes and Endocrinology, Baltimore, told Medscape Medical News that changing the Dietary Guidelines for Americans in this way would be confusing for consumers, many of whom already are puzzled about nutrition recommendations.

But if future research confirms this study's findings, Ms. Ginn said, "Dieticians and diabetes educators may need to rethink their stance on limiting consumption of saturated fats."

Yet she cautioned that full-fat dairy items, such as whole milk, typically contain more calories than lower-fat options and may have adverse health effects on the heart. She said she would continue to tell her diabetic patients to choose low-fat milk options for every day.

"This study gives us permission to be a little indulgent with a full-fat dairy item now and then," she said.

Although the new study suggests that refined carbohydrates may have an effect on metabolic dysfunction, perhaps in part by increasing circulating amounts of even-chain saturated fatty acids, Ms. Ginn concluded, "The benefits may not be just about the fat but the whole diet. People eat foods in combination. Moderation remains key."

This study was funded by the European Union's Sixth Framework Programme for Research and Technological Development, Medical Research Council's Epidemiology Unit and Human Nutrition Research, and Cambridge Lipidomics Biomarker Research Initiative. Dr. Forouhi has reported no relevant financial relationships. Disclosures for the coauthors are listed in the article. Dr. Mozaffarian has received honoraria from Bunge, Pollock Institute, and Quaker Oats; has done consulting for Foodminds, Nutrition Impact, Amarin, AstraZeneca, and Life Sciences Research Organization; is a member of the Unilever North America scientific advisory board; and has received royalties from UpToDate. He is supported by a grant from the National Heart, Lung, and Blood Institute. Ms. Ginn has disclosed no relevant financial relationships.

Lancet Diabetes Endocrinol 2014. Published onlineAugust 6, 2014. Article, Editorial

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