Types of Fat

In the San Luis Valley Diabetes Study a high intake of fat was associated with an increased risk of IGT and type 2 diabetes. In the 1 to 3 year follow-up of this study, fat consumption predicted the progression to type 2 diabetes in persons with IGT (25).

A positive association has also been found between saturated fat and hyperglycemia or glucose intolerance in cross-sectional studies (5,25). However, large cohort studies with diagnosed type 2 diabetes as an end point did not show an appreciable association with saturated fat intake (26).

Conversely, a high intake of vegetable fat was inversely associated with the risk of type 2 diabetes during 6 years of follow-up among participants in the Nurses’ Health Study who were not obese (26).  With the exception of the San Luis Valley Diabetes Study,  other epidemiological   studies   did   not   find   a   significant   association   between   intakes   of monounsaturated fat and risk of type 2 diabetes (25). However, fats of a different nature are often highly correlated in the diets, and therefore confounding by one type of fat may have hindered the analysis for another type of fat. 

The relationship between nature of dietary fat and type 2 diabetes has been studied in persons with IGT and undiagnosed type 2 diabetes patients who were reported to have higher proportions of saturated fatty acids in serum cholesterol esters than persons with normal glucose tolerance (27).

Perhaps the best evidence for the potentially deleterious effect of saturated fatty acids comes from the KANWU Study. In this study, replacing an appreciable proportion of dietary saturated fatty acids with monounsaturated fatty acids was associated with an increase in insulin sensitivity (28).

It is also of interest to note that both in the Finnish Diabetes Prevention Study and in the US Diabetes Prevention Project, which showed a reduced risk of progression from IGT to type 2 diabetes, the dietary recommendations included advice to appreciably reduce saturated fatty acids. No studies are yet available to suggest conclusive associations between trans-fatty acids and the risk of type 2 diabetes.

The suggestion that n   -  3 polyunsaturated fatty acids may also play a role in the development of type 2 diabetes came from a prospective study of 175 elderly men and women who were habitual fish eaters. They were shown to have a 50% lower risk of developing glucose intolerance over a follow-up period of 4 years compared with persons who were not regular fish eaters (29).

It now appears that the effects of various fatty acids on the risk of type 2 diabetes are similar to their effects on lipoprotein-mediated risk of coronary heart disease (30 - 32).

According to the available data, modifying intake of dietary fats towards consuming less saturated fat and more unsaturated fats may reduce the risk of developing type 2 diabetes - in addition to reducing cardiovascular risk.