Q: It makes sense that eating lots of unhealthy fats would lead to heart disease . But why do health experts say that sugar is also bad for your heart?
A: Excess fat and salt are well-known dietary villains, especially when it comes to heart health. But mounting evidence is why excess sugar has joined the list.
It's not that all sugar is bad. We need glucose to power our cells, especially our brain cells. What matters the most is how dietary sugar is packaged.
Sugar occurs naturally in all foods that contain carbohydrates, such as fruits, vegetables, legumes and whole grains. These types of foods have a low glycemic index. That means that our digestive system breaks them down more slowly into glucose and other simple sugars prior to absorption.
On the other hand, refined sugars used to make breakfast cereals, pastries, sodas, fruit drinks, and other sweet foods and beverages primarily contain glucose and fructose. They have a high glycemic index because these simple sugars are rapidly absorbed into our blood stream.
High glycemic index foods cause blood sugar levels to shoot up. In response, cells in the pancreas churn out extra insulin. This hormone helps cells sponge up glucose. But that surge of insulin also signals the body to store extra glucose as fat.
When you eat healthier carbohydrates that are low on the glycemic index, blood sugar and insulin levels climb more slowly and don't crest as high as they do with quickly digested carbohydrates.
Higher blood sugar and insulin levels increase your risk of heart disease. According to a recent study done over 15 years, people who got 17 percent to 21 percent of their calories from added sugar had a 38 percent higher risk of dying from cardiovascular disease compared with those who consumed 8 percent of their calories as added sugar.
Exactly how excess sugar might harm the heart isn't clear. Drinking sugar-sweetened beverages can raise blood pressure. A high-sugar diet also causes the liver to convert glucose and fructose into harmful fats, which then get dumped into the bloodstream. Both factors are known to boost heart disease risk.
What's more, sugar delivers "empty calories" -- calories unaccompanied by fiber, vitamins, minerals, and other nutrients. Too much added sugar often crowds healthier foods from a person's diet.
(Howard LeWine, M.D. is an internist at Brigham and Women's Hospital in Boston and assistant professor at Harvard Medical School.)
For additional consumer health information, please visit www.health.harvard.edu.)
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