Which fats are linked with diabetes risk?

We've reported in the past on the results of the PREDIMED study (Prevencion con Dieta Mediterranea). To briefly recap, this long-term, large scale study compared three groups of people, all of whom were at least 55 years of age (at the start of the study) and at increased risk of cardiovascular disease. The three groups were: a control group, who followed a low-fat diet; a Extra-Virgin Olive Oil group, who received a daily allotment of 1 1/2 ounces of olive oil along with counseling regarding a Mediterranean Diet; and a Mixed Nuts group, who received a 1-ounce daily allotment of mixed nuts and the same Mediterranean Diet counseling as the EVOO. One previous article, for example, showed that those in the EVOO group were 40% less likely to develop diabetes than those in the low-fat diet group, and those in the Mixed Nuts group were 30% less likely.

In today's article the authors dig deeper into the risk of diabetes (Am J Clin Nutr 2017;105:723-35). For this analysis they excluded any participants who had type 2 diabetes at the start of the study, along with those who lacked initial glucose scores or food frequency questionnaires (both of these, among other tests, were administered yearly throughout the study).

Those food frequency questionnaires allowed the authors to identify the sources and types of fats in the participants' diets, differentiating between animal sources of fat and plant sources of fat along with the types of fats: saturated, polyunsaturated and monounsaturated, omega-3s and omega-6s (and whether they are from animals or plants), and trans-fats.

For their analysis the researchers took into account a host of other factors, including sex; Body Mass Index; physical activity; whether the participant had high blood pressure or took high blood pressure medications; nutrient intake including protein, fiber, and cholesterol; glucose levels; total caloric intake; and other food types.

When the authors limited their analysis to the first food frequency questionnaire, administered at the start of the study, they saw no association between the participants' intake of saturated fat and fat from animal sources and their risk of developing type 2 diabetes, although the amount of total fat (from all sources) was indeed linked to a higher risk. However, after updating the participants' fat intake with information from each yearly dietary questionnaire, the authors began to see a slightly different pattern. Those whose intake of saturated fats was in the top 25% of intake were more than twice as likely to develop type 2 diabetes than those whose saturated fat intake was in the bottom 25%. When the authors looked at fat from animal sources they saw similar results. Butter and cheese intake, specifically, were both associated with higher risk of diabetes, while whole-fat yogurt actually decreased the risk.

Even more interesting are the results when the authors separated the results by which group the participants had been assigned to: Mediterranean Diet (either with nuts or with olive oil) or low fat diet. Those in the Mediterranean Diet groups had only a slight increase in their risk of diabetes when their intake of total fat was in the top 25%. The control (low-fat diet) group increased their risk by 27%. The highest intake of monounsaturated fats meant a 28% reduction in risk of diabetes for those following the Mediterranean Diet, while those on the low-fat diet saw their risk increase by 38%.

What this means for you

When considering these results, we must remember that those following a Mediterranean-style diet will have less animal fats in their diets since one of the tenets of a Mediterreanean Diet is less meat and leaner meats. Further, the Mediterranean Diet groups would consume more monounsaturated fats due to their intake of nuts and olive oil, and the latter especially would likely be replacing saturated fats such as butter with monounsaturated fats (the olive oil). This study shows that it's the source of the fats, especially the saturated fats, that matters most: cutting all fat is not the answer.

First posted: July 12, 2017