In this study there was no consistent relation between consumption of various carbohydrate foods and risk of acute myocardial infarction. Carbohydrate intake in the Italian population is peculiar, as Italy shows the highest consumption of carbohydrates from refined cereals among affluent countries31
—that is, up to more than 300 g/day in the highest quintile of consumption. The main sources of carbohydrates in the Italian population are white bread and its substitutes (such as crackers, grissini, and melba toasts) and various types of pasta or rice dishes, accounting altogether for almost 40% of the total carbohydrate intake.32
Consumption of sugar and cakes is relatively low in Italy32
and was not associated with risk for acute myocardial infarction in this study. We found no significant association of myocardial infarction risk with whole grain food consumption, although a tendency for a decreased odds ratio emerged. An inverse association between whole grain intake and risk of ischaemic heart disease has been reported in the Iowa Women’s Health Study cohort, which was attributed to the phytochemicals, fibre, and antioxidants contained in such foods.5
However, in this Italian population only 6.2% of cases and 8.5% of controls consumed whole grains and in relatively low amounts, potentially explaining the lack of a significant protection in this study.
Diets with a high consumption of refined carbohydrates (high glycaemic index foods) tend to raise blood glucose and insulin concentrations to a greater extent than slowly absorbed carbohydrates (low glycaemic index foods), such as legumes and whole grains,33,34
and have been directly associated with risk of coronary heart disease,4,9
type 2 diabetes,9,16,17
Our data do not support the hypothesis of a strong effect of glycaemic index and glycaemic load on the risk of acute myocardial infarction, although a moderately increased odds ratio associated with high glycaemic index foods was found in selected categories of subjects, such as people over 60 years of age and in people with a body mass index > 25 kg/m2
. This latter result can be related to impaired insulin resistance in elderly overweight subjects and is in agreement with the results of the Nurses’ Health Study, which found a doubled risk of coronary heart disease with a high glycaemic load in women with a body mass index of
, but not in those with lower body mass index.4
No differences by sex were found in our study for the relation of glycaemic index and glycaemic load to risk of acute myocardial infarction. In this analysis we excluded subjects with diabetes. However, if the glycaemic load is related to type 2 diabetes, as several investigators have suggested,16,17
then there may still be a link between glycaemic load and coronary heart disease, albeit indirect.
With regard to potential sources of bias, in this study cases and controls were interviewed in the same hospitals and came from the same geographical area; participation was almost complete; and patients admitted for chronic conditions or diseases related to known or potential risk factors for acute myocardial infarction or modification of diet were excluded from the comparison group. The potential confounding of covariates associated with acute myocardial infarction risk in this study,36,37
including energy intake, was allowed for in the analysis. The food frequency questionnaire was satisfactorily valid and reproducible21–23
and there is no reason to assume different recall of intake of bread, pasta, and other carbohydrates on the basis of the disease status, because the possibility of a relation between these foods and acute myocardial infarction was unknown to most subjects.
Glycaemic index estimates have some limitations, as some of them derive from small samples and their variability is unclear.25,26,38
Statistics on the average glycaemic index and glycaemic load in the Italian population are not available; however, intake of bread and pasta were similar in our controls and in the general population.32,39
Another limitation of this study is its relatively small sample size, which is inadequate to investigate moderate associations in subgroups or interactions. However, these data are of considerable interest given the paucity of available information on glycaemic index, glycaemic load, and coronary heart disease risk, and the originality of the population studied in terms of carbohydrate amount and carbohydrate composition of diet.32
Although no overall relation with glycaemic index or glycaemic load and acute myocardial infarction risk was found in this Italian population, there was a positive association between glycaemic index and acute myocardial infarction in subgroups most likely to have insulin resistance—the older and more overweight subjects. More studies in these high risk subgroups are needed to confirm these observations and to identify foods or classes of foods with specific effects.