Women who eat a high-carbohydrate diet — especially if they eat a lot of bread, pizza, jam, and similar products — are at an increased risk of coronary heart disease, researchers said.The same effect, however, wasn’t seen in men, according to Vittorio Krogh, MD, of the Fondazione IRCCS Istituto Nazionale dei Tumori in Milan, and colleagues.
The finding comes from a large prospective study of nearly 45,000 Italian volunteers who were followed for more than seven years on average, Krogh and colleagues said in the April 12 issue of Archives of Internal Medicine.
The analysis, studying causes of cardiovascular disease, looked at Italians taking part in the long-running European Prospective Investigation into Cancer and Nutrition (EPIC) study, the researchers said.
Participants’ diets were assessed using a questionnaire, from which the researchers calculated the glycemic index, a measure of how much a carbohydrate raises blood glucose levels compared with glucose or white bread. They also calculated the glycemic load, defined as the product of the glycemic index of a food and its carbohydrate content.
Foods with a high glycemic index included bread, sugar or honey and jam, pizza, and rice, while foods with a low glycemic index included pasta, fruit, and cakes.
For each participant, the average glycemic index was the sum of the indices for each food they ate, multiplied by how much they ate and the percentage of carbohydrates, and divided by the total daily carbohydrate intake.
The glycemic load calculation was similar, but without dividing by carbohydrate intake. For the analysis, participants were divided into quartiles based on carbohydrate intake.
Over the follow-up period, the researchers found, there were 463 new cases of coronary heart disease among the 44,132 participants, including 305 among the 13,637 men and 158 among the 30,495 women.
For both men and women, the average daily glycemic load increased by about 50% from the lowest to the highest quartile, Krogh and colleagues reported in the journal.
In a multivariate analysis, they said, women with the highest carbohydrate intake had a significantly greater risk of heart disease than did those in the lowest quartile. The relative risk was 2.0, with a 95% confidence interval from 1.16 to 3.43.
Those in the second and third quartiles were also at significantly elevated risk, compared with the lowest quartile, and the trend was significant at P=0.02, they found.
Increasing carbohydrate intake from foods with a high glycemic index was also associated with increasing heart disease risk. Compared with the lowest quartile, those in the highest group had a relative risk of 1.68, with a 95% confidence interval from 1.02 to 2.75. The trend was significant at P=0.04.
On the other hand, there was no significant increase in risk if the increased carbohydrate intake came from foods with a low glycemic index, the researchers found.
Among men, on the other hand, there were no significant associations linking carbohydrate intake and coronary heart disease, they said.
There is some evidence, they said, that changes in HDL cholesterol and triglycerides are stronger risk factors for cardiovascular disease for women than men. Such a difference might explain the lack of association found among men in the study, they said.
The study’s strengths include its prospective design, the researchers said. As well, the researchers used glycemic index values set for Italian foods, rather than using international tables.
On the other hand, they said, the questionnaires were not designed to estimate dietary glycemic index and load. In addition, they were only administered once, and some participants may have changed their diets over the study period.