People with diabetes have a two- to fourfold increased risk of coronary heart disease, and an increased risk of mortality due to the low HDL with high triglyceride syndrome that is seen in Type 2 diabetes, even when well treated. Epidemiological evidence suggests that populations of people with diabetes who consume a low-fat diet have a lower mortality rate, see “Nutritional Management of Cardiac Risk Factors in Type 2 Diabetes” & “Effect of Variations in Amount and Kind of Dietary Fat and Carbohydrate in the Dietary Management of Type 2 Diabetes” sections.
Reducing intake of saturated fat can lower levels of total and LDL cholesterol, risk factors for coronary heart disease. The recommended level is less than 10% energy from saturated fat. Although there are no large studies of diabetic populations it is considered appropriate to base the prevention and management of heart disease on the same principles as in non-diabetic populations.
Individual fatty acids have different effects, with lauric, myristic and palmitic having a hypercholesterolaemic effect and stearic being neutral.
Trans Fatty Acids
Most trans fatty acids are formed during partial hydrogenation of vegetable oils to produce margarine and certain baked foods including biscuits and pastries. Trans fatty acids have a similar impact on lipid levels as saturated fat, decreasing HDL and increasing LDL. Specific information relating to people with diabetes is lacking but there are some large studies that show the evidence is not conclusive regarding coronary risk and trans fatty acid intake.
The Nurses Health Study shows that high intakes of foods that are a significant source of trans fat may be associated with a risk of coronary heart disease. The EURAMIC study however found no significant effect.
Polyunsaturated Fats (n-6)
The WHO recommendation for the general population is a maximum intake of 3 – 7% dietary energy. This is because polyunsaturated fats are more susceptible to oxidation and therefore more atherogenic. In addition, a reduction in HDL may occur when larger amounts are consumed.
Fish Oils (n-3)
The general recommendation with regard to fish oils for the population as a whole is not to take therapeutic doses but to consume one helping of oily fish per week.
Increasing fish intake in the non-diabetic population is associated with reduced mortality from coronary heart disease. However, despite available evidence showing that fish oils can reduce plasma triglycerides and VLDL concentrations in the diabetic population, as well as reducing blood pressure, there are also potential deleterious effects of fish oils on LDL cholesterol and glycaemic control in people with diabetes.
In the Mediterranean, where the prevalence of coronary heart disease is lower, the typical diet is high in monounsaturated fatty acids.
The beneficial effects of monounsaturated fats include the fact that they are more resistant to lipid peroxidation and increased MUFA intakes have also been associated with lower daytime blood pressures. There have been studies in both diabetic and non-diabetic populations which show falls in total cholesterol with no changes in HDL levels or triglyceride levels. The choice of MUFA as the prime source of dietary fat is therefore recommended.
Restriction of saturated fat will also limit intake of cholesterol. The EASD recommendations refer to a maximum intake of 300 mg/day.