Fatty foods are harder to stomach as you age. Put down that greasy slice of pizza and read this.

Pizza, burgers and other greasy, fatty dishes might be considered their own food group when you’re younger. But throwing back high-fat meals can be tough on your gastrointestinal tract as you age.

If you feel a bit queasy or even straight-up uncomfortable after a fat-heavy dinner, you’re not alone. Fatty food intolerance, aka fat malabsorption, is common as you get older. “Things change as you age — your body’s ability to break down fats is one of them,” Dr. Mir Ali, medical director of MemorialCare Surgical Weight Loss Center in Fountain Valley, Calif., tells Yahoo Life.

Of course, it can be hard to connect the dots with any food intolerance, let alone one that’s related to fat. But if you’ve been struggling with digestion recently and you’re not sure what’s happening, a fatty food intolerance is worth looking into. Here’s what it is and why it happens.

What is fatty food intolerance?

Fatty food intolerance occurs when your gastrointestinal tract has trouble breaking down fat, Auriel Willette, associate professor at Rutgers Robert Wood Johnson Medical School, tells Yahoo Life. “As we age, the digestive system undergoes subtle but meaningful changes that can make fatty foods more difficult to tolerate,” he says.

This causes the stomach to empty more slowly because it takes more time to absorb fatty foods, Willette says. “By extension, you can have these fatty foods staying in the stomach and small intestine longer. Basically, what was once an easy, unconscious process becomes far more difficult for an older digestive system.”

Your intestines rely on a series of muscle contractions to push food through, Ashley Baumohl, a dietitian at Northwell Lenox Hill Hospital, tells Yahoo Life. “This mechanism, known as peristalsis, can weaken with age,” she says. “Think of a conveyer belt that has slowed down, and the luggage keeps piling up.” As a result, “that fried food you handled fine at 25 might hit differently in your 60s,” she says.

What causes it?

There are a few different things happening here beyond slower gut muscles.

• Your liver produces less bile. Bile is a digestive fluid produced by the liver that’s used to help break down fats. “The acidity [in bile] helps to emulsify and digest unsaturated and particularly saturated fats,” Willette says. So less bile can impact digestion.

• Your gut microbiome changes. As you get older, your gut microbiome (made up of tons of microorganisms that live in your digestive tract and play an important role in your health) becomes less diverse, favoring bacteria that promotes inflammation, Willette says. Some of these microbes can also slow down how long it takes for food to move through your gut, raising the risk of fat intolerance, he says.

• Your intestinal lining isn’t the same as it used to be. As you get older, your body may produce less insulin, which is a hormone that helps regulate your blood sugar, aka glucose. That can cause an increase of glucose in your body, which can damage your intestinal lining, Willette says. “That further impacts [fat] absorption,” he adds.

What are its symptoms?

It can be tricky to pinpoint any food intolerance, let alone one most people have never heard of. But according to Willette, there are a few signs that fatty foods may not be sitting well with you after a meal:

• You have nausea

• You’re dealing with indigestion or reflux

• You feel generally uncomfortable

The toilet bowl may offer some clues too. Your stool may look greasy, foamy, be light-colored or especially smelly if you’re having trouble digesting fat, according to Cleveland Clinic.

Are some fatty foods worse than others?

All fats aren’t created equal, Bethany Doerfler, a gastrointestinal research specialist at the Northwestern Medicine Digestive Health Institute, tells Yahoo Life. “The amount of fat in our diet may not be as important as the type of fat we eat,” she says. “Plant-based fats rich in unsaturated fats, such as avocado, olive oil, nuts and seeds are less likely to cause negative gastrointestinal effects.”

But Willette says that ultra-processed, high-fat foods like potato chips, fries, pastries and sausages are some of the biggest offenders. “These tend to be the most difficult to digest because they contain saturated or trans fats, which not only take more energy to break down, but are more inflammatory by nature,” he says.

The way fat-rich foods are prepared matters too, according to Willette. “Deep frying or smoking, while tasty, will compound all of the problems associated with ultra-processed foods,” he says.

Your fat intolerance may be a sign of something more serious

Fat intolerance is a normal part of aging, but it tends to be situational, Ali says. That means you might feel uncomfortable after having a heavy steak dinner or fried chicken, but that discomfort is temporary.

“Persistent or severe symptoms could point to more serious conditions,” Willette says, citing gallbladder dysfunction, pancreatic insufficiency or bile acid malabsorption as possible issues. But it can also be a sign of a metabolic condition like prediabetes or even irritable bowel syndrome, he says.

Does this mean you can’t have fatty foods anymore?

Not necessarily. If you suspect you’re dealing with a fatty food intolerance, Ali recommends paying close attention to how you feel after you eat. “Try different foods and see what works for you,” he says. “If you feel uncomfortable after having fried, greasy foods, decreasing them would help.”

Willette agrees that moderation — and some careful planning — is the way to go. “Eating smaller portions of fatty foods as a sort of ‘accent’ alongside fiber-rich food, leafy greens or the like can reduce digestive load and make it easier to absorb the whole meal,” he says.

The quality of your food matters too, he says. “High-quality fat sources from whole foods, or foods that are minimally processed, are much better because your body does not have to process preservatives and other non-essential agents alongside the food item itself,” Willette says. That’s why Doerfler recommends avocado or hummus as a sandwich topper rather than cheese or bacon, for example, or cooking with olive oil. “If you want higher-fat meat or french fries, choose them occasionally and the smallest portion possible,” she says.

Of course, you don’t have to have greasy, fatty foods in your diet, and Ali points out that scaling back on them isn’t a bad idea for people of any age. “This is good for your overall health as well,” he says.

If you seem to be struggling to digest fatty foods or are concerned that something else may be going on with your health, Willette recommends talking to your doctor or a dietitian. “They can offer guidance on what is likely normal and what may reflect an underlying disease process,” he says.