There is no longer any debate about whether dietary fat plays a role in the etiology of type-2 diabetes (T2D). Research has clearly shown that elevated blood fatty acid concentrations, regardless of type, promote insulin resistance and glucose intolerance, and that even a single high-fat meal can elevate concentrations of liver fat by three- to five-fold. Nonetheless, when it comes to dietary fat there is a distinct difference among not only the various fatty acids but also the foods that supply them. This raises some interesting questions regarding recommendations to replace saturated fat with polyunsaturated fats based on epidemiological evidence because depending on how fat intake was measured, results have been inconsistent.
To fill this gap, researchers from Sweden conducted an analysis of 26,930 middle-aged men and women from the MDC cohort of South Sweden. What made this study unique was that the main objective of the MDC cohort was to examine fat intake specifically, which ultimately led to very detailed information regarding the fat content and fatty acid composition of numerous foods. Over the 14-year follow-up period of the cohort, just over 10% were diagnosed with T2D. Not surprisingly, these individuals were older with a higher body fat percentage and waist circumference, worse glucose and lipid panels, and more sedentary time.
Moving on to the point of interest, total dietary fat intake among those with and without T2D was not statistically different and averaged between 38-39% of total caloric intake. In line with this was the fact that total intake of saturated, monounsaturated, and polyunsaturated fatty acids had no association with T2D. The only exception was fatty acids shorter than 14 carbons in length, which showed a protective effect against the chances of developing T2D. This includes myristic acid, lauric acid, and all the short- and medium-chained fatty acids below them. Notably, long-chained saturated fatty acids such as palmitic and stearic acid, as well as the omega-3 fatty acids and the omega-3 to omega-6 ratio had no association.
Regarding actual foods, high-fat dairy (both fermented and non-fermented) was incredibly protective; this included whole-fat milk, cheese, cream, and butter. Conversely, margarine and oils had no association, and eggs and red meat were detrimental. For completeness, pastry and biscuit intake was also protective.
It is no coincidence that dairy fat is rich in short- and medium-chained fatty acids, as well as potentially beneficial trans-fatty acids such as conjugated linoleic acid. This is not the first study to document associations between high-fat dairy intake and health either. Observational evidence from cohorts in Europe and the USA have suggested dairy fat to be protective against T2D, and clinical trials have supported these findings. Dairy is the most important source of total and saturated fat in the Swedish diet, contributing 30% of total fat intake and 35% of saturated fat intake, and this appears to be a good dietary habit. However, the limitations of observational research present themselves in the other findings and consequently warrant skepticism with all conclusions from this study. Namely, interventional trials have shown consumption of both eggs and red meat to not be detrimental to glucose tolerance or other metabolic risk factors of type-2 diabetes.