When the U.S. Department of Agriculture cracked down on Americans' sugar intake earlier this year, the agency blamed the average 15 teaspoons we eat daily for a host of health problems and advised that we limit it to less than 10 percent of our total calories. (That's about 12 teaspoons a day for a woman who eats a 2,000-calorie diet). And while it's pretty easy to understand how sugar leads to tooth decay or obesity, it's less obvious how it hurts other parts of the body, such as your heart.
But sugar's effect on your cardiovascular system is no minor side effect: A landmark 2014 study published in JAMA Internal Medicine found that people who consumed about a fifth of their calories from added sugar over 15 years had twice the chance of dying from heart disease as those who took in less than 10 percent. The effect held true for men and women of all ages, regardless of how frequently they exercised or their BMI.
"The risk goes up slowly, then accelerates after a certain point. We've found that threshold," says lead study author Quanhe Yang, PhD, a heart disease researcher at the U.S. Centers for Disease Control and Prevention. He points out that it doesn't take much to cross into the danger zone. "For many Americans, all they have to do is drink one can of soda [with more than 9 teaspoons of sugar] to put them over the 20 percent mark," he says.
So what's going on inside the body to cause such damage to the heart? Although researchers don't have a clear understanding of the exact mechanisms, they agree that sugar's ill effects are working on several different levels to increase heart disease risk factors, such as high blood pressure, bad cholesterol, and triglycerides. Of course, being obese or developing type 2 diabetes also increases your risk of heart disease - two conditions linked with a surge of sugar intake, especially sugar-sweetened beverages.
Here are some other ways sugar is wreaking havoc on your heart:
Are you carrying extra pounds around the waist? Doctors call it "sugar belly." That's a sign you might have underlying metabolic syndrome, a cluster of symptoms - large waist size, high triglycerides, total cholesterol or HDL levels, blood pressure, and blood sugar - that boost your risk for chronic heart trouble, which affects one in five people in the United States, according to the American Heart Association.
If you're consuming heavy doses of fructose, you can develop fatty liver disease like an alcoholic.
"There's a reason fat goes around your belly. Sugar is toxic to your liver the same way as alcohol," explains Laura Schmidt, PhD, professor of health policy at the University of California at San Francisco and founder of the educational website Sugar Science.
The kind of sugar called fructose (as in high-fructose corn syrup) is almost exclusively metabolized in the liver. "If you're guzzling a 64-ounce soda, you're blasting your liver," Dr. Schmidt says. "What it can't mobilize as energy will get selectively deposited around the gut. If you're consuming heavy doses of fructose, you can develop fatty liver disease like an alcoholic."
Luckily, there's one sweet substance that can reverse the damage and protect you from heart disease: Fruit is processed differently by the body and has phyto-nutrients that reduce inflammation, she says.
Consuming too much fructose (which, along with glucose, makes up cane sugar) also causes your pancreas to go into overdrive, producing insulin in an attempt to regulate your blood sugar. "The fat in the liver is hindering the ability of insulin to do its job. That leads to insulin resistance," explains Kimber Stanhope, PhD, a nutritional biologist at the University of California at Davis.
That means the receptors on cells that take in blood sugar stop working the way they should. Not only is insulin resistance linked to heart disease, the train wreck of events can even mess with the hunger hormone leptin, which tells the brain it's time to stop eating and interrupts your ability to know when you're full.
Yes, eating too much sugar is bad news all around for your heart. The effect was so dramatic that Dr. Stanhope published a study in 2015 with nearly 200 healthy adults and found that those who drank beverages containing 25 percent high-fructose corn syrup before each meal had abnormal levels of lipids (fat globules floating around in your bloodstream) and uric acid - both risk factors for heart disease - in as little as two weeks. Even the group that drank beverages with 10 percent high-fructose corn syrup saw dangerous changes in their bodies.
"That's the same as adding a half-can of cola at breakfast, lunch, and dinner," says Stanhope. "There's never going to be a definitive study showing excess sugar causes heart disease, but all this evidence put together should be enough to convince the average person to eat less of it."