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 impairs immune function (1, 2).
This article lists 10 foods that may weaken your immune system.
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1. Added sugar
There’s no doubt that limiting how much added sugar you consume promotes your overall health and immune function.
Foods that significantly raise blood sugar, such as those high in added sugars, increase the production of inflammatory proteins like tumor necrosis alpha (TNF-α), C-reactive protein (CRP), and interleukin-6 (IL-6), all of which negatively affect immune function (3).
This is especially pertinent in people with diabetes, as they can have elevated blood sugar levels for longer than people with well-regulated blood sugar levels.
What’s more, having high blood sugar levels may inhibit the response of neutrophils and phagocytes, two types of immune cells that help protect against infection (4).
Furthermore, it has been shown that high blood sugar levels may harm gut barrier function and drive gut bacteria imbalances, which can alter your immune response and make your body more susceptible to infection (5, 6).
For example, a 2012 study in 562 older adults found that those who had elevated blood sugar levels also had lower immune responses and higher levels of the inflammatory marker CRP (7).
Similarly, many other studies have linked high blood sugar levels to an impaired immune response in people with and without diabetes (8, 9, 10).
Additionally, diets high in added sugar may increase the susceptibility to certain autoimmune diseases, including rheumatoid arthritis, in some populations (11, 12, 13).
Limiting your intake of foods and beverages high in added sugar, including ice cream, cake, candy, and sugary beverages, can improve your overall health and promote healthy immune function.
Studies have associated high blood sugar levels with impaired immune response. Limiting your intake of sugary foods and beverages can promote better blood sugar management and immune response.
2. Salty foods
Salty foods like chips, frozen dinners, and fast food may impair your body’s immune response, as high salt diets may trigger tissue inflammation and increase the risk of autoimmune diseases.
In a 2016 study, 6 healthy men first consumed 12 grams of salt per day for 50 days. This was followed by around 50 days of consuming 9 grams of salt per day and then consuming 6 grams per day for a similar duration. Lastly, they consumed 12 grams daily for another 30 days (14).
On the high salt diet containing 12 grams per day, the men had higher levels of white blood cells called monocytes and inflammatory markers IL-23 and IL-6. They also had lower anti-inflammatory protein IL-10, indicating an excessive immune response (14).
Salt may also inhibit normal immune function, suppress anti-inflammatory response, alter gut bacteria, and promote the generation of immune cells that are implicated in the pathogenesis of autoimmune diseases (15, 16).
In fact, researchers believe that excessive salt intake may be associated with the increase in autoimmune diseases in Western countries (17).
Additionally, eating too much salt has been shown to worsen existing autoimmune diseases like ulcerative colitis, Crohn’s disease, rheumatoid arthritis, and lupus (18).
Therefore, reducing your intake of table salt and high salt foods may benefit your immune function.
Studies show that a high salt intake may impair normal immune function, promote inflammation, and increase your susceptibility to autoimmune diseases.
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 proteins that may weaken the immune response, while diets higher in omega-3 fats reduce the production of those proteins and enhance immune function (19, 20).
What’s more, studies in people with obesity indicate that a high dietary intake of omega-6 fats may lead to immune dysfunction and increase the risk of certain conditions like asthma and allergic rhinitis (19, 21).
However, the relationship between omega-6 fats and the immune response is complicated, and more human research is needed (22).
Regardless, researchers recommend that you maintain 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 (3).
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 canola oil, corn oil, and soybean oil.
Eating more omega-3-rich foods and fewer omega-6-rich foods may promote optimal immune function.
4. Fried foods
Fried foods are high in a group of molecules called advanced glycation end products (AGEs). AEGs are formed when sugars react with proteins or fats during high temperature cooking, such as during frying.
If levels become too high in your body, AGEs can contribute to inflammation and cellular damage (23).
AGEs are thought to weaken the immune system in several ways, including by promoting inflammation, depleting your body’s antioxidant mechanisms, inducing cellular dysfunction, and negatively affecting gut bacteria (24, 25, 26).
As such, researchers believe that a diet high in AGEs may increase susceptibility to diseases like malaria and increase the risk of medical conditions like metabolic syndrome, certain cancers, and heart disease (27, 28, 29).
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 (23).
Fried foods aren’t good for overall health and may cause immune dysfunction. Fried foods are high in AGEs and should be limited in any healthy diet.
5. Processed and charred meats
Like fried foods, processed and charred meats are high in AGEs.
For example, a 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 contents (23).
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 (19).
Plus, diets high in saturated fat may contribute to systemic inflammation and harm immune function (30, 31, 32).
Additionally, a high intake of processed meats and charred meat has been linked to various diseases, including colon cancer (33, 34).
Diets high in processed meat and meats cooked at high temperatures have been linked to increased disease risk and may harm your immune system.
6. Fast food
Fast food has been linked to many negative health outcomes. Eating it too frequently 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 bacteria imbalance in the gut, all of which can negatively affect your immune health (35).
Fast food can also contain the chemicals bis(2-ethylhexyl) phthalate (DEHP) and diisononyl phthalate (DiNP), which are two types of phthalates. Phthalates can leach into fast food, for example, through packaging or plastic gloves worn during food preparation (36).
Phthalates are known to disrupt your body’s endocrine, or hormone-producing, system. They may also increase the production of inflammatory proteins that can weaken your immune response to pathogens and cause immune dysregulation (37, 38, 39).
In addition, phthalates may reduce gut bacteria diversity, which can negatively affect your immune system (38, 40).
Keep your intake of fast food to a minimum. Eating too much of it is associated with health risks and may harm 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 emulsifiers, which are added to processed foods to improve texture and shelf life, can alter gut bacteria, harm your gut lining, and induce inflammation, all of which can cause immune dysfunction (41).
Carboxymethylcellulose (CMC) and polysorbate-80 (P80) are commonly used emulsifiers that have been linked to immune dysfunction in rodent studies (42, 43).
Similarly, human and animal studies have shown that the common additive carrageenan may induce intestinal inflammation and inhibit immune response, although more research is needed to better understand these effects (44, 45, 46, 47, 48, 49).
Lastly, corn syrup, salt, artificial sweeteners, and the natural food additive citrate may also negatively affect your immune system (41).
Ultra-processed foods contain additives like emulsifiers, thickeners, and sweeteners that may affect immune function.
8. Highly refined carbs
Eating highly refined carbs like 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 (3, 4).
Plus, a diet rich in refined carbs may alter gut bacteria, which can negatively affect your immune system (5, 50).
Choosing nutritious, high fiber carb sources like starchy vegetables, oats, fruit, and legumes over refined carbs is smart to support immune health.
A diet high in refined carbs may adversely affect your immune system. Choosing more nutritious carb sources like fruits and starchy vegetables is a better choice for your overall 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, thus inhibiting immune function. High fat diets may also increase your susceptibility to infection by suppressing your immune system and white blood cell function (51, 52).
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 (53, 54).
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.
Eating a diet high in saturated fat may impair immune function. Following a balanced, high fiber diet is likely a good way to support immune health.
10. Artificially sweetened foods and beverages
Certain artificial sweeteners have been linked to altered gut bacteria composition, increased inflammation in the gut, and blunted immune response (55, 56, 57).
Increasing evidence suggests that artificial sweeteners, including sucralose and saccharin, may induce gut bacteria imbalances. Some researchers postulate that overusing artificial sweeteners may be detrimental to immune health (40, 58, 59).
Furthermore, some research in rodents and limited case studies in humans also suggests that a high intake of artificial sweeteners may contribute to the progression of autoimmune diseases. However, more research is needed (60, 61).
That said, not all studies agree, and some have shown that moderate daily intake of those sweeteners does not cause changes in gut bacteria or immune function (62, 63).
Artificial sweeteners have been associated with alterations in gut bacteria that may harm immune function. Additionally, some research suggests that high intake may contribute to the progression of autoimmune diseases.
The bottom line
You can support your immune system by living a healthy lifestyle.
This means limiting foods and beverages that are high in added sugars and salt, processed meats, and fried foods, all of which may have adverse effects on your body’s immune function.
To support your immune system, it’s best to follow a balanced diet rich in whole, nutrient-dense foods and limit your intake of ultra-processed foods as much as possible.