People who cut out saturated fatty acids while upping their intake of white bread, pasta and other refined carbohydrates that can cause blood sugar to spike aren't doing their heart any favours, new research from Denmark shows.
But reducing saturated fatty acid intake while eating more whole grain bread, vegetables (aside from potatoes), and other carbohydrates with a less dramatic effect on blood sugar may improve heart health, Dr Marianne U. Jakobsen of Aarhus University Hospital and her colleagues found.
"The type of carbohydrate matters," Jakobsen said.
How the study was done
A recent analysis of 21 studies including 350 000 people found "no significant evidence" that saturated fat in and of itself increased heart disease risk, but the authors of that analysis suggested that what people replaced those saturated fat kilojoules with might be more important.
A subsequent study found that this was indeed the case; people who upped their polyunsaturated fatty acid intake while cutting saturated fat showed improved heart health.
In the current study, Jakobsen and her team looked at the carbohydrate side of the equation. Specifically, they accounted for the "glycemic index" of different types of carbohydrates. Glycemic index is a measure of how quickly blood sugar jumps after eating a particular type of carbohydrate.
Low glycemic index foods tend to be high in fibre and less refined, such as foods made from whole grains; high glycemic foods are often lower in fibre and more highly refined, and include white bread, pasta made from white flour, and bananas.
To investigate how increasing carb intake while reducing saturated fatty acid intake affected the heart, the researchers looked at 53 644 men and women who had never suffered heart attacks.
During follow-up, which averaged about 12 years, nearly 2 000 heart attacks were documented.
Jakobsen and her team divided the study participants into three groups based on the average glycemic index of the carbohydrates in their diet, and then calculated heart attack risk based on the composition of their diet.
What the study showed
They found that heart attack risk fell by 12% for every additional 5% of a person's total kilojoule intake that came from carbohydrates -- if a person's average dietary glycemic index was low.
However, this reduction wasn't statistically significant, meaning it could have been due to chance. But among the people with the highest average dietary glycemic index, every 5% increase in carbohydrate kilojoules upped heart attack risk by 33%.
For people whose average glycemic index fell in the middle, an increase in carb intake along with a reduction in saturated fatty acid intake had no effect on heart risk.
"We cannot say that saturated fatty acids are not associated with increased risk of coronary heart disease because it depends on what you compare," Jakobsen said.
Unfortunately, she added, figuring out the glycemic index of a particular food is not straightforward. "It's a scientific way of classifying foods, so it's not really public-health-friendly," she said. Nevertheless, the researcher added, people can likely decrease their glycemic index by eating "less refined foods." - (Reuters Health, April 2010)