You’ve probably long forgotten why you’re supposed to dislike high fructose corn syrup so much.

You know food and drink containing this cheap artificial sweetener is bad for your health. That’s for sure.

But why? Now you’ll know — we’ve done the research for you.

Where It Comes From

High fructose corn syrup starts as corn starch, which is nothing more than a link of glucose molecules. When separated into individual molecules, it becomes corn syrup — or 100 percent glucose. To this simple sugar, HFCS adds enzymes that convert some glucose into fructose, another simple sugar.

The “high” in HFCS refers to the amount of fructose compared to pure-glucose corn syrup. The typical form of HFCS contains either 42 percent or 55 percent fructose, according to the Food and Drug Administration. The rest is glucose and water.

The FDA recommends that people limit consumption of all added sugars, including HFCS.

“Limiting is the key when discussing all added sugars, including high fructose corn syrup,” says Jennifer Feda, Clinical Nutrition Manager at the Hospital of Central Connecticut in New Britain. “The Dietary Guidelines for Americans (issued by the U.S. Department of Agriculture and Department of Health and Human Services) recommends limiting added sugar to less than 10 percent of total calories daily.”

Why HFCS Is Bad For You

More than two-thirds of Americans are either obese or overweight. Added sugars and high fructose corn syrup are considered primary causes of the overweighting of America. Weight gain abetted by high-calorie foods containing HFCS can also contribute to heart disease, diabetes, fatty liver disease and dyslipidemia, an abnormal level of cholesterol and other fats in the blood. Fructose becomes a more universal threat to your body by accumulating as visceral fat around your organs.

HFCS also adds to natural bacteria in our intestines, which can produce bloating and gas.

It’s not just HFCS: Any sweetener, including table sugar, can contribute to these health problems. For food manufacturers, HFCS is a much cheaper sweetener than sugar.

It’s the fructose in both table sugar and HFCS — each is about half glucose, half fructose — that’s most detrimental to our health. Our bodies break down starch-derived carbohydrates, like rice, into glucose that’s a vital exercise energy source and readily distributed  throughout our body. Fructose, however, must be converted by the liver to glucose, glycogen or fat before being available as an energy source.

“Chronic overconsumption of high fructose corn syrup causes an increase in fat production and worsens insulin sensitivity,” says Feda. “Even a small change like not drinking regular soda is beneficial. Limiting processed foods in general will not only help you limit intake of high fructose corn syrup, but also your intake of unhealthy fats, which is a bonus.”

HFCS is everywhere, from processed foods to ice cream and flavored yogurt, breakfast cereals and everyday condiments like ketchup and mustard.

“These foods have sugars added during processing and are not a natural source of sugar,” says Feda. “Natural sugars are found in fruit, milk and vegetables.”

It’s so prevalent that an HFCS-averse consumer must actually check a product label for a “no high fructose corn syrup” alert.

You might already check the labels routinely. Now you know why.