Sometimes, a juicy cheeseburger and an order of hot, crispy fries simply call your name. (Greasy foods are so beloved that they have an entire day devoted to them; National Greasy Foods Day is October 25.) While it’s fine to give in to your cravings now and then, it’s important to know how your nutrition choices, and those greasy foods in particular, affect your health.
Does greasy food cause acne? Why does it make your stomach feel weird? And why is greasy food bad for you, anyway? We consulted Ayla Barmmer, a Boston-based registered dietitian, to find out. Here’s what eating greasy foods does to your body.
1. It strains your digestive system
“When we eat greasy foods like fried food, the sheer volume of fat puts a lot of pressure on our digestive system,” Barmmer said in an email to TIME. Of fat, carbs and protein, fat is the most slowly digested, and it requires enzymes and digestive juices, like bile and stomach acid, to break it down, she says. Everything from stress to medication can lower levels of these digestive juices, so many people are deficient to begin with, Barmmer says. Add in fat, and your digestive system will be working overtime, often leading to bloating, nausea and discomfort.
2. It makes you run to the bathroom
The most common symptom of digestive strain is an unpleasant one. “Not only will food just sit in your stomach, but it may enter the intestines inadequately digested,” Barmmer says. “Sometimes you wind up seeing greasy or oily stools in these cases.” Many people also experience diarrhea and stomach pain after eating greasy food.
3. It throws your gut bacteria out of whack
More and more evidence suggests that what you eat affects your gut bacteria, also known as your microbiome. Downing a cheeseburger and fries, Barmmer says, isn’t doing those microorganisms any favors. “Greasy foods do not contain the nourishing, healthy fats that we find in things like avocados, fish, extra virgin olive oil and even butter,” she says. Eating more refined vegetable oils than nourishing fats, she says, tips the body’s balance of fatty acids, which in turn may throw off everything from hormone levels to immune health.
4. Greasy food may cause acne
You may not see zits directly after a big meal, but Barmmer says that greasy food likely does play a role in acne. “The effect is indirect, occurring over time and as a result of a dietary pattern of eating,” she says. “Acne is largely caused by hormonal imbalances and/or bacterial imbalances, so greasy foods cause acne by way of harming gut health.”
5. It raises your risk for heart disease and diabetes
If your diet consistently includes greasy foods, Barmmer says, you’ll likely see your risk for chronic conditions—particularly heart disease—go up. A 2014 study from researchers at the Harvard T.H. Chan School of Public Health found that people who ate fried foods between four and six times per week saw their risk for Type 2 diabetes climb 39%, and their risk for coronary heart disease increase by 23%. For people who ate it every day, those percentages only got higher.