Whole-Fat Milk and Cheese Can Lower Diabetes Risk

The incidence of Type 2 diabetes declined significantly as levels of a fatty acid found in whole-fat dairy products increased....

Adults with the highest levels of trans-palmitoleic acid had a 60% lower diabetes incidence compared with individuals who had the lowest levels. Higher levels of the fatty acid also were associated with a more favorable metabolic profile.

Multivariate analyses of demographic, clinical, and lifestyle factors showed that whole-fat dairy consumption had the strongest association with levels of trans-palmitoleate. However, the authors remained circumspect about the association.

Dariush Mozaffarian, MD, DrPH, of the Harvard School of Public Health, and coauthors wrote in conclusion that, "Our results demonstrate an inverse relationship between levels of trans-palmitoleate and metabolic risk factors and diabetes incidence."

"The small differences in trans-palmitoleate levels raise questions about whether this is the active compound or a marker for some other, unknown protective constituent of dairy or other ruminant foods."

The findings support previous evidence of favorable associations between whole-fat dairy consumption and metabolic factors. The authors speculated that trans-palmitoleate could exert effects on pathways related to insulin resistance, dyslipidemia, and hepatic fat synthesis.

A product of endogenous fat synthesis, circulating palmitoleic acid has been associated with protection against insulin resistance and metabolic dysregulation in experimental models. Studies in humans, however, have yielded mixed results, the authors wrote in the introduction to their findings.

Efforts to study circulating palmitoleic acid have been confounded by the effects of endogenous synthesis and metabolism. The trans isomer of palmitoleate represents an endogenous source of the fatty acid and avoids confounding endogenous effects. Derived primarily from naturally occurring dairy and other ruminant trans fats, trans-palmitoleate is not associated with increased cardiovascular risk, in contrast to trans fats derived from partially hydrogenated oils.

"In fact, several studies have demonstrated inverse associations between dairy consumption and risk for insulin resistance, the metabolic syndrome, or diabetes," the authors continued. "To our knowledge, no previous studies have evaluated a potential role of trans-palmitoleate in metabolic risk."

The patient cohort of the Cardiovascular Health Study provided an opportunity to examine associations between trans-palmitoleate, metabolic risk factors, and risk of Type 2 diabetes. Mozaffarian and coauthors analyzed data on 3,736 study participants, all of whom were 65 or older and were identified from Medicare eligibility lists.

Baseline assessments included physical examination, diagnostic testing, questionnaires about health status, and laboratory evaluation that included measurement of 45 different fatty acids. Study participants were followed for 10 years, including annual clinic visits and interim telephone calls.

Laboratory results showed that trans-palmitoleate accounted for an average of 0.18% of total fatty acid. Levels had a strong correlation with known biomarkers of dairy-fat consumption but a weak correlation with biomarkers of partially hydrogenated oils.

Whole-fat dairy consumption had the strongest association with trans-palmitoleate levels. Separate analyses of different types of dairy foods further refined the association by showing that levels of the fatty acid were most closely associated with whole-milk consumption. Levels of trans-palmitoleate were not significantly related to consumption of carbohydrates, protein, red meat, or low-fat dairy foods.

In multivariate analyses, higher trans-palmitoleate levels were significantly associated with:

Lower body mass index (-1.8%, P=0.058)
Smaller waist circumference (-1.8%, P=0.009)
Higher levels of HDL cholesterol (1.9%, P=0.043)
Lower triglyceride levels (-19.0%, P<0.001)
Lower total cholesterol:HDL ratio (-4.7%, P<0.001)
Lower levels of C-reactive protein (-13.8%, P=0.050)
Lower fasting insulin levels (-13.3%, P=0.001)
Less insulin resistance by homeostasis model (-16.7%, P<0.001)
During follow-up, 304 study participants developed new-onset diabetes. In adjusted analyses, comparison of trans-palmitoleate quintiles showed that participants in quintiles 4 and 5 had diabetes hazard ratios of 0.44 and 0.36, respectively, compared with quintile 1 (P<0.001 for trend).

"Each higher standard deviation of trans-palmitoleate was associated with a 28% lower risk of diabetes," the authors wrote.

Acknowledging limitations of the study, Mozaffarian and colleagues noted that trans-palmitoleate levels were measured at a single point in time and that food intake was based on self-reports. They also pointed out that causality cannot be determined due to the possibility of residual confounding and that "the small differences in trans palmitoleate levels raise questions about whether this is the active compound or a marker for some other, unknown protective constituent of dairy or other ruminant foods."