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. 

But sometimes your immune system is triggered to go into overdrive. This is also not good for your health. An overactive immune system can result in autoimmune diseases, chronic inflammation, and allergies. 

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It turns out, what you eat affects your immune system quite a bit. Your gut contains lots of good bacteria that you need to stay healthy. And 70% to 80% of your immune cells are there, too.

So, the quality of what goes into your digestive system affects your immune function. Read on to learn about seven kinds of food to avoid to help your immune system work for you.

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 fiber. Grains may be refined for taste, appearance, or so that a product lasts longer on the shelf. But without the fiber, many of the health benefits are lost. 

Foods with less fiber also make you feel less full. So, you may tend to eat more. Refined grains also cause your blood sugar to rise faster. Both of these things contribute to excess weight. And that’s another risk factor for your immune system.

Common foods made with refined grains include:

• Cakes and pastries

• Many breakfast cereals

• White rice

• Corn grits

• White bread

• Bagels

• Flour tortillas

• Foods made with white or all-purpose flour

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Food packaging can be tricky. It may take a little detective work to know how much whole grain or refined grain there is in a product. Look for “100% whole grain” items. You can also check the ingredient list and food label. The whole grain should be first or second on the ingredient list. For example, the ingredients may contain “whole wheat flour” or “whole oats.” And products made with whole grains will have more fiber.

2. Ultra-processed foods

Ultra-processed foods are changed in a lot of ways during manufacturing. A food might be processed or ultra-processed so that it:

• Looks or tastes different

• Is easier or faster to produce or transport

• Lasts longer on the shelf

• Is more convenient to prepare or eat

Most ultra-processed foods contain a long list of additives and preservatives. Most of these were approved for food safety long ago. And once they’re approved, they’re usually not tested again.

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

Also, most ultra-processed foods are 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 may put your body at risk for infections. Or you may be more prone to chronic inflammation, autoimmune diseases, allergies, or cancer.

Common 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 foods

• 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 heavily processed. 

3. Fried foods

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

First, they tend to be high in calories. And things are often fried to make them taste good, which probably means eating a lot of calories all at once. Doing that on a regular basis can lead to extra weight, which isn’t good for the immune system.

The second reason is that the kind of oil that’s used in frying may be bad for your immune system. Many oils, even if they’re made from plants, are higher in omega-6 fatty acids. We need omega-6 fatty acids in our diet. They help the immune system to fight infections. Many healthy foods contain them. But consuming more omega-6 than omega-3 fatty acids may increase the risk of inflammatory diseases. 

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

The oils with the highest percentage of omega-6 fatty acids are:

• Corn

• Soybean

• Cottonseed

• Sunflower

Butter, palm oil, and coconut oil have lower amounts of omega-6, but they’re high in saturated fat. That can stress the immune system, too. 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 salt in a typical diet comes from packaged or processed foods. The recommended amount of daily sodium for adults is less than 2,300 mg per day. But the average daily intake in the U.S. is 3,400 mg per day. 

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

A high-salt diet has been linked to inflammation. That can make some chronic and autoimmune conditions worse, like eczema and multiple sclerosis. Chronic inflammation is also an important factor in 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. 

Some ways to make sure you’re taking in a healthy amount of sodium or salt include the following:

• Check the percentage for the daily allowance of sodium on the food label. Less than 5% per serving is low. More than 20% per serving is high.

• Opt for fresh fruits and vegetables whenever possible.

• Limit your intake of processed and instant foods.

• Try to add herbs and spices for flavor instead of salt.

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

• Psoriasis

• Multiple sclerosis

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

Most sugar in a typical diet is hidden in the foods we eat. And often, it’s found in foods you might not think of as being sweet. Many beverages also contain a lot of sugar.

So, 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.

Names of some added sugars you might see on a list of ingredients include: 

• 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, may increase inflammation in some people. That may occur more if the meat is processed. 

In fact, any kind of processed or cured meat is more likely to affect the immune system. Processed meats include things like:

• Bacon

• Lunch meat or sandwich meat

• Hot dogs

• Sausages

• Jerky

• Canned meat

Most experts recommend limiting red meat to 2 servings or fewer per week. And 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. Heavy drinking can also 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 often drink a lot of alcohol. But a night of binge drinking can also put your immune system at risk.

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

• For men: 2 drinks or less 

• For women: 1 drink or less 

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 

Why trust our experts?

Written by:

Anne Jacobson, MD, MPH

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

Edited 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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