Additional reporting by Evan Yandrisovitz.

If you have high cholesterol, your doctor may have told you that one way to get your levels under control is to change your diet and lose weight. In fact, losing just 5% of your total weight can be enough to improve your cholesterol levels, according to one study where participants who hit this target significantly reduced their levels of low-density lipoprotein (LDL) cholesterol, total cholesterol, and triglycerides.

Losing body fat can help reduce LDL, the so-called “bad cholesterol,” and triglycerides in your bloodstream that contribute to clogged arteries and heart disease. But there are some good ways and bad ways to lose weight when you have high cholesterol, and it’s important to know the difference.

Two popular weight-loss diets—the low-carb, high fat keto diet and intermittent fasting (extending the time between meals to burn more calories and consume fewer)—are both diets you may want to reconsider if you have high cholesterol, and that’s because both recommend drinking a high-fat beverage called “butter coffee” as a breakfast replacement.

Typically made by adding one or two tablespoons of unsalted butter and a tablespoon of coconut oil, butter coffee is the worst possible beverage for people concerned about high cholesterol due to its high levels of fat, says registered dietitian Susan Bowerman, MS, RD, senior director of worldwide nutrition education and training for Herbalife Nutrition.

What is butter coffee and why is it bad for cholesterol?

“If you look at a typical butter coffee recipe, which calls for a cup of coffee with a tablespoon of butter and a tablespoon of coconut oil in it, you’re getting 19 grams of saturated fat and 25 grams total fat, which is a lot more than what would be recommended,” Bowerman says.

The American Heart Association recommends that only 5% to 6% of your daily calories come from saturated fat; that’s roughly 13 grams of saturated fat if you’re consuming about 2,000 calories a day.

“When we counsel people on reducing their total cholesterol in their bloodstream, the thing we focus on most is saturated fat,” says Bowerman, who recommends people get their fats from healthier sources like olive oil, avocado, fish, and nuts. “I know (coconut oil) is really popular because it’s plant-based, but it’s still a highly saturated fat and those tend to drive up blood cholesterol.”

Related: Popular Snacks for Lowering Cholesterol.

Buttered coffee was made popular among fans of the keto and intermittent fasting diets after entrepreneur and biohacker Dave Asprey wrote a best-selling book called The Bulletproof Diet and coined the term “bulletproof coffee,” to describe the buttery coffee concoction. Asprey claims he lost 80 pounds after he started drinking buttered coffee as his only breakfast even though it contained more than 400 calories per cup.

What is cholesterol?

Cholesterol is a “lipid,” a waxy fat in the bloodstream that’s made by your body and also comes from food. It’s made up of high-density lipoprotein (HDL), the so-called “good cholesterol” because it lowers bad LDL or low-density lipoprotein. Another lipid in the is very-low-density (VLDL), very-low-density lipoprotein, which carries triglycerides through the bloodstream.

Low-density lipoproteins are dangerous because they can leave fatty deposits, or plaque (atherosclerosis), on the walls of your arteries, potentially causing blockages.

But I don’t drink butter coffee…

You don’t have to add butter and coconut oil to your coffee to do your heart a disservice. The worst drink for your cholesterol could also be coffee lightened with whole milk, heavy cream, or half-and-half, because those contain saturated fat, too, although in not nearly as high levels as butter or coconut oil. And if you’re a fan of those flavored, blended “coffee drinks,” like lattes and frappuccinos that are popular at cafes, you may be consuming as much, if not more, saturated fat than you find in butter coffee.

For example, those frozen chai lattes from Dunkin Donuts or The Grande White Chocolate Mocha with whipped cream from Starbucks may put you over your recommended saturated fat limit for the day, says Bowerman.

Dunkin’s large frozen chai latte has 12 grams of fat and seven saturated while The Grande White Chocolate Mocha has 18 grams of total fat and 12 grams of saturated.

Bowerman notes that most people tend to worry about the calories and sugar in flavored coffee drinks and overlook the total amount of fat these morning beverages contain. “When you start getting into (additives) like some of the syrups and flavorings, like these chocolates and mochas, those themselves are additional sources of saturated fat, too,” she says.

For beverages that should never pass your lips, read The Worst Drinks on the Planet.