7 Foods to Avoid for a Healthy Immune System

Your immune system is your body’s built-in protection. When it’s working well, it keeps out most of the unwelcome visitors without you even knowing it. But it runs on a complex network of cells, proteins, and chemicals. This means there are many ways your immune system can be stressed.

Sometimes, your immune system has a hard time keeping up. When it’s not performing well, you may get more infections. This may even contribute to some forms of cancer. 

Other times, your immune system is triggered to go into overdrive. This isn’t healthy either. An overactive immune system can result in autoimmune diseases, chronic inflammation, and allergies. 

What you eat affects your immune system quite a bit. Your gut is home to lots of good bacteria that you need to stay healthy. And 70% to 80% of your immune cells live there, too.

So, the quality of the foods that go into your digestive system affect your immune function. Read on to learn about seven kinds of food that can weaken your immune system.

1. Refined grains

Fiber plays an important role in keeping your digestive system healthy. It keeps food and waste products moving along, which prevents constipation. But fiber also helps your immune system. The healthy bacteria in your gut use fiber to stimulate your immune cells to work better. 

Refined grains go through a process that removes their fiber. Grains may be refined for taste, appearance, or a longer shelf life. But without the fiber, many of their health benefits are lost. 

Foods with less fiber also make you feel less full, so you may end up eating more. Refined grains can also cause your blood sugar to rise faster. Both of these things contribute to excess weight — another risk factor for your immune system.

Common foods made with refined grains include:

• Cakes and pastries

• Many breakfast cereals

• White rice

• White pasta

• Corn grits

• White bread

• Bagels

• Flour tortillas

• Foods made with white or all-purpose flour

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Food labels can be tricky. It may take a little detective work to know how much whole grain a product really has. Look for items labeled “100% whole grain.” You can also check the ingredient list and food label. Whole grain should appear first or second on the ingredient list. For example, you might see “whole wheat flour” or “whole oats.” Products made with whole grains will have more fiber.

2. Ultra-processed foods

Ultra-processed foods are foods that have been changed a lot from their original form during manufacturing. A food might be processed or ultra-processed to:

• Look or taste different

• Be easier or faster to produce or transport

• Last longer on the shelf

• Be more convenient to prepare or eat

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Most ultra-processed foods have a long list of additives and preservatives. Most of these were approved for food safety long ago. Once they’re approved, they usually aren’t tested again.

The immune system is an active area of study. Newer evidence suggests that some chemicals in processed foods may not be good for your immune system.

Ultra-processed foods are often made with refined grains and have a lot of added fat, salt, and sugar. They’re also low in the vitamins and minerals your immune system needs. Eating too many ultra-processed foods can raise your risk for infections. Or you may be more prone to chronic inflammation, autoimmune diseases, allergies, or cancer.

Common examples of ultra-processed foods include:

• Packaged cakes, cookies, and sweets

• Chips and snack foods

• Packaged breakfast bars, rolls, and buns

• Ready-to-eat, microwavable, and instant meals

• Most fast foods and many restaurant foods

If a food’s list of ingredients has a lot of chemical names that are hard to pronounce, it’s probably highly processed. 

3. Fried foods

Fried foods can stress your immune system in a couple of ways. 

First, they’re often high in calories. Because fried foods taste good, people tend to consume them in large amounts, so they get a lot of calories all at once. Eating this way regularly can lead to extra weight, which isn’t good for your immune system.

Second, the type of oil used for frying may also be bad for your immune system. Many frying oils, even plant-based ones, are high in omega-6 fatty acids. We need omega-6 fatty acids in our diet. They help our immune system to fight infections and are found in many healthy foods. But it’s possible that consuming more omega-6 than omega-3 fatty acids may increase your risk of inflammatory diseases. (Research on this is still very controversial.)

Fried foods absorb a lot of oil. So, most fried foods contain high amounts of omega-6 fatty acids. This can make it harder to eat enough omega-3 fatty acids for your immune system to be in a healthy balance. 

Seed oils sometimes have a reputation of being potentially harmful, though recent research suggests this may not be deserved. Still, it’s important to consume oils with the highest percentage of omega-6 fatty acids in moderation. These are:

• Corn oil

• Soybean oil

• Cottonseed oil

• Sunflower oil

Butter, palm oil, and coconut oil have less omega-6 but are high in saturated fat. That can also stress your immune system. And it’s always best to avoid trans fats.

If you fry foods at home, olive oil and avocado oil are healthier options. But those oils aren’t used in most prepared foods or restaurant foods.

4. Salty foods

Most of the salt in a typical diet comes from restaurant and processed foods. The recommended daily sodium limit for adults is less than 2,300 mg — and ideally, it should be closer to 1,500 mg. But in the U.S., the average daily intake is about 3,400 mg per day. 

Too much sodium stresses your cardiovascular system and kidneys. But it can also affect your immune system. 

A high-salt diet has been linked to inflammation. That can worsen some chronic and autoimmune conditions, like eczema and multiple sclerosis. Chronic inflammation is also a risk factor for cardiovascular disease, kidney disease, and liver disease.

Too much sodium can also have a direct effect on the cells that fight infection. A high-sodium diet has been found to make a certain type of immune cell — called neutrophils — less effective. These are blood cells that fight bacterial infections. 

To make sure you’re taking in a healthy amount of sodium or salt, try:

• Checking the “% Daily Value” for sodium on the food labels — less than 5% per serving is low and more than 20% per serving is high

• Opting for fresh fruits and vegetables whenever possible

• Limiting your intake of processed and instant foods

• Using flavorful substitutes for salt, like herbs, spices, or lemon juice

5. Foods and drinks with added sugar

Eating too much sugar also leads to inflammation. Studies have found a link between excess sugar intake and autoimmune diseases such as: 

• Rheumatoid arthritis

• Inflammatory bowel disease (IBD)

• Psoriasis

• Multiple sclerosis

Eating a lot of sugar can also lead to excess weight gain. And that can lead to even more inflammation.

It helps to know how to look for added sugars on a nutrition label. The goal is for less than 10% of your daily calories to come from added sugars. But many packaged and processed foods contain more than that in just one serving.

Keep in mind that sugar can be “hidden” in foods. There’s often sugar in foods you might not think of as being sweet. Added sugars go by many different names on ingredients lists, including: 

• Corn syrup

• High-fructose corn syrup

• Dextrose, fructose, sucrose, glucose, lactose, or maltose

• Brown sugar or raw sugar

• Fruit nectars

• Honey, maple syrup, or molasses

• Cane juice or malt syrup

6. Red meat and processed meat

Eating red meat, like beef, pork, and lamb, can increase inflammation in some people. This is more likely when the meat is processed. 

In fact, any kind of processed or cured meat is more likely to affect your immune system. These include:

• Bacon

• Lunch meat or sandwich meat

• Hot dogs

• Sausages

• Jerky

• Canned meat

Most experts recommend limiting red meat to two servings or fewer per week. Processed meats should be eaten only occasionally.

7. Alcohol

Drinking alcohol — especially heavy drinking — can affect your immune system in some important ways. It can decrease the healthy gut bacteria that your immune system needs to function. And heavy drinking can affect the number of immune cells your body produces.

This can lead to inflammatory conditions. But it also leaves you more vulnerable to infections. This can happen for people who regularly drink a lot of alcohol. But even one night of binge drinking can put your immune system at risk.

If you choose to drink alcohol, it’s best to limit your daily intake to:

• 2 drinks or less for men

• 1 drink or less for women 

Binge drinking is defined as having the following amounts on a single occasion:

• For men: 5 drinks or more 

• For women: 4 drinks or more

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Written by:

Anne Jacobson, MD, MPH

Anne Jacobson, MD, MPH has been a board-certified physician since 1999. She was a full-scope family physician (inpatient, outpatient, obstetrics, and office procedures) in the Cook County Ambulatory Health Network for 15 years.

Edited by:

Meredith Hoffa

Meredith Hoffa is a senior health editor at GoodRx, where she leads journalists and clinicians covering various well-being topics, particularly in diet and nutrition.

Reviewed by:

Katie E. Golden, MD

Katie E. Golden, MD, is a board-certified emergency medicine physician and a medical editor at GoodRx.

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