10 Foods That May Weaken Your Immune System

Your diet affects how you feel and how well your body functions.

While a nutrient-dense, well-rounded diet supports your immune system, a diet that’s low in nutrients and high in ultra-processed foods can impair immune function.

This article lists 10 foods that may weaken your immune system.

1. Added sugar

There’s no doubt that limiting your consumption of added sugar promotes overall health and immune function.

Foods that significantly raise your blood sugar, such as those high in added sugars, increase the production of inflammatory proteins such as tumor necrosis factor alpha, C-reactive protein (CRP), and interleukin-6 (IL-6), all of which negatively affect immune function.

This is especially relevant for people with diabetes because the condition interferes with blood sugar regulation. In those with diabetes, foods high in added sugar may cause blood sugar levels to stay high for longer after eating than they would in people without that condition.

High blood sugar levels can affect the response of white blood cells in your immune system, requiring them to work harder to protect against infections.

Furthermore, high blood sugar levels may harm gut barrier function and drive gut bacteria imbalances. This can change your immune response and make your body more vulnerable to infection.

Many other studies have also linked high blood sugar levels to an impaired immune response in people with and without diabetes.

Additionally, diets high in added sugar may increase susceptibility to certain autoimmune diseases, including rheumatoid arthritis, in some populations.

Limiting your intake of foods and beverages that are high in added sugar, such as ice cream, cake, candy, and sugary drinks, can improve your overall health and promote healthy immune function.

2. Salty foods

High salt diets may trigger tissue inflammation and increase the risk of autoimmune diseases. Therefore, salty foods such as chips, frozen dinners, and fast food may impair your body’s immune response.

In a small 2014 study, 6 healthy men first consumed 12 grams (g) of salt per day for 50 days. They then consumed 9 g of salt per day for 50 days, followed by 6 g per day for a similar duration. Lastly, they consumed 12 g daily for another 30 days.

On the high salt diet containing 12 g per day, the men had higher levels of white blood cells called monocytes and higher levels of the inflammatory markers IL-23 and IL-6. They also had lower levels of the anti-inflammatory protein IL-10, which indicates excessive immune response.

Salt may also inhibit immune function, suppress anti-inflammatory response, alter gut bacteria, and promote the production of immune cells involved in autoimmune diseases.

In fact, researchers believe that excessive salt intake may be associated with the increase in autoimmune diseases in Western countries.

Additionally, eating excess salt has been shown to promote inflammation in existing autoimmune diseases such as ulcerative colitis, Crohn’s disease, rheumatoid arthritis, and lupus.

Therefore, reducing your intake of table salt and high salt foods may benefit your immune function.

3. Foods high in omega-6 fats

Your body needs both omega-6 and omega-3 fats to function.

Western diets tend to be high in omega-6 fats and low in omega-3s. This imbalance has been associated with increased disease risk and possibly immune dysfunction.

Diets high in omega-6 fats seem to promote the expression of pro-inflammatory lipids (fats) that may weaken the immune response. In contrast, diets higher in omega-3 fats reduce the production of those lipids and enhance immune function.

What’s more, studies in people with obesity indicate that a high dietary intake of omega-6 fats may lead to immune dysfunction and an increased risk of certain conditions, such as asthma and allergic rhinitis.

However, the relationship between omega-6 fats and the immune response is complicated, and more research in humans is needed.

Regardless, researchers recommend maintaining a healthy balance of omega-6 to omega-3 fats, which is considered to be around 1:1 to 4:1, to promote overall health.

This means eating more foods that are high in omega-3s — like salmon, mackerel, sardines, walnuts, and chia seeds — and fewer foods that are high in omega-6s, such as sunflower oil, canola oil, corn oil, and soybean oil.

4. Fried foods

Fried foods are high in a group of molecules called advanced glycation end products (AGEs). AGEs form when sugars react with proteins or fats during high-temperature cooking, such as frying.

If AGE levels become too high in your body, they can contribute to inflammation and cellular damage.

AGEs are thought to weaken the immune system in several ways, such as by promoting inflammation, depleting the body’s antioxidant mechanisms, inducing cellular dysfunction, and negatively affecting gut bacteria.

For this reason, researchers believe that a diet high in AGEs may increase susceptibility to some diseases, such as malaria. It may also increase the risk of medical conditions like metabolic syndrome, certain cancers, and heart disease.

Cutting back on fried foods like French fries, potato chips, fried chicken, pan-fried steak, fried bacon, and fried fish will reduce your intake of AGEs.

5. Processed and charred meats 

Like fried foods, processed and charred meats are high in AGEs.

For example, a 2013 study that analyzed the AGE content of 549 foods found that fried bacon, broiled hot dogs, roasted skin-on chicken thighs, and grilled steak had the highest AGE content.

Processed meats are also high in saturated fat. Some research suggests that diets high in saturated fats and low in unsaturated fats may contribute to immune system dysfunction.

Additionally, diets high in saturated fat may contribute to systemic inflammation and harm immune function.

Researchers have also found that a high intake of processed meats and charred meat is linked to various diseases, including colon cancer.

6. Fast food 

Fast food has been linked to many negative health outcomes. Eating it too often may also take a toll on your immune system.

Diets high in fast food and highly processed foods may drive inflammation, increase gut permeability, and cause a bacterial imbalance in your gut, all of which can negatively affect your immune health.

Also, fast food might contain the chemicals bis(2-ethylhexyl) phthalate (DEHP) and diisononyl phthalate (DiNP), which are two types of phthalates. Phthalates can leach into fast food from packaging or from plastic gloves worn during food preparation.

Phthalates are known to disrupt your body’s endocrine (hormone-producing) system. They may also increase the production of inflammatory proteins that can weaken your immune response to pathogens and cause immune dysregulation.

In addition, phthalates may reduce gut bacteria diversity, which can negatively affect your immune system.

7. Foods that contain certain additives

Many food items, especially ultra-processed foods, contain additives to improve shelf life, texture, and taste. Some of these may negatively affect your immune response.

For example, some food manufacturers add emulsifiers to processed foods to improve texture and shelf life. These can alter your gut bacteria, harm your gut lining, and induce inflammation, all of which can cause immune dysfunction.

Carboxymethylcellulose (CMC) and polysorbate 80 (P80) are commonly used emulsifiers that have been linked to immune dysfunction in rodent studies.

Similarly, human and animal studies have shown that the common additive carrageenan may promote intestinal inflammation and change the composition of the gut bacteria.

However, in some cases, carrageenan might have an antioxidant effect and other possible benefits.

More research is needed to better understand how carrageenan affects human health and immunity.

Salt, artificial sweeteners, and the natural food additive citrate may also negatively affect your immune system.

8. Highly refined carbs

Eating highly refined carbs such as white bread and sugary baked goods too often may harm your immune system.

These are types of high-glycemic foods that cause a spike in your blood sugar and insulin levels, potentially leading to the increased production of free radicals and inflammatory proteins like CRP.

Plus, a diet rich in refined carbs may alter your gut bacteria, which can negatively affect your immune system.

Choosing nutritious, high fiber carb sources like starchy vegetables, oats, fruit, and legumes over refined carbs is a good way to support your immune health.

9. Certain high fat foods

A diet high in saturated fats and low in unsaturated fats has been associated with immune dysfunction.

High saturated fat intake can activate certain signaling pathways that induce inflammation, which can reduce immune function. High fat diets may also increase your susceptibility to infection by suppressing your immune system and white blood cell function.

Additionally, rodent studies have suggested that high fat diets can cause gut bacteria changes and damage the intestinal lining, potentially increasing infection and disease risk.

Researchers are still investigating how different fatty acids affect the immune system, and more human studies are needed.

That said, eating a well-balanced diet high in fiber and healthy fat sources is likely a good way to support immune health. Foods such as olive oil, avocado, salmon, nuts, and seeds contain healthy fats.

10. Artificially sweetened foods and beverages

Certain artificial sweeteners have been linked to changes in gut bacteria composition, increased inflammation, and blunted immune response.

Increasing evidence suggests that artificial sweeteners, including sucralose and saccharin, may induce gut bacteria imbalances. Some researchers suggest that overuse of artificial sweeteners may harm immune health.

Some older research in rodents and limited case studies in humans also suggest that a high intake of artificial sweeteners may contribute to the progression of autoimmune diseases. However, more research is needed.

That said, not all studies agree, and some have found that moderate daily intake of those sweeteners does not change the gut bacteria or immune function.

The Food and Drug Administration (FDA) has set acceptable daily levels of consumption for artificial sweeteners and states that these sweeteners are safe when consumed at those levels.

The bottom line

You can support your immune system by limiting your consumption of processed meats, fried foods, and foods and drinks that are high in added sugars and salt. All of these foods may negatively affect your body’s immune function.

To promote overall health and immune function, it’s best to eat a balanced, varied diet; consume whole, nutrient-dense foods whenever possible; and limit your intake of ultra-processed foods.