your diet can affect how you feel and how your body functions.
while a nutrient-dense, well-rounded diet can support your immune system, a diet low in nutrients and high in ultra-processed foods can impair immune function (1, 2).
this article lists 10 foods that may weaken the immune system.
1. add sugar
no doubt limiting the amount of added sugars you consume can boost your overall health and immune function.
Foods that significantly raise blood sugar, such as foods high in added sugar, increase the production of inflammatory proteins such as tumor necrosis α (TNF-α), C-reactive protein (CRP), and interleukin-6 (IL-6), all of which hurt immune function (3).
this is especially important for people with diabetes because their blood sugar levels rise for longer periods compared to people whose blood sugar levels are well regulated.
what's more, high blood sugar levels may inhibit the response of neutrophils and phagocytes, two immune cells that help prevent infection (4).
in addition, it has been shown that high blood sugar levels can impair gut barrier function and lead to an imbalance of gut bacteria, which can alter your immune response and make your body more susceptible to infection. （5, 6）。
For example, a 2012 study of 562 older adults found that people with elevated blood sugar levels had lower immune responses and higher levels of CRP, a marker of inflammation. （7）。
similarly, many other studies have linked high blood sugar levels to impaired immune responses in both diabetic and non-diabetic patients. （8, 9, 10）。
in addition, a high-sugar diet may increase the susceptibility of certain populations to certain autoimmune diseases, including rheumatoid arthritis. （11, 12, 13）。
limiting your intake of high-sugar foods and beverages, including ice cream, cakes, sweets, and sugary drinks, can improve your overall health and promote healthy immune function.
summary: studies have shown that high blood sugar levels are associated with an impaired immune response. limiting the intake of sugary foods and beverages can promote better blood sugar management and immune response.
2. savory food
salty foods such as potato chips, frozen dinners, and fast food can damage your body's immune response, as a high-salt diet can trigger tissue inflammation and increase the risk of autoimmune diseases.
in a 2016 study, six healthy men first consumed 12 grams of salt per day for 50 days. this is followed by about 50 days of consuming 9 grams of salt per day, and then 6 grams of salt per day at similar times. finally, they consumed 12 grams (14) per day for the next 30 days.
Men have higher levels of white blood cells in a high-salt diet of 12 grams per day, called monocytes and inflammatory markers IL-23 and IL-6. They also have a lower anti-inflammatory protein, IL-10, indicating an excessive immune response. （14）。
salts can also inhibit normal immune function, inhibit anti-inflammatory responses, alter gut bacteria, and promote the production of immune cells associated with the pathogenesis of autoimmune diseases. （15, 16）。
in fact, the researchers believe that excessive salt intake may be related to an increase in autoimmune diseases in western countries. （17）。
in addition, excessive salt intake has been shown to aggravate existing autoimmune diseases such as 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.
summary: research shows that high salt intake may impair normal immune function, promote inflammation, and increase your susceptibility to autoimmune diseases.
3. foods high in omega-6 fat
your body needs omega-6 and omega-3 fats to function properly.
western diets tend to be rich in omega-6 fats, while omega-3 fats are low. this imbalance is associated with an increased risk of disease and possibly immune dysfunction.
diets rich in omega-6 fats appear to promote the expression of pro-inflammatory proteins, which may weaken the immune response, while diets rich in omega-3 fats reduce the production of these proteins and boost immune function. （19, 20）
in addition, studies of obese people have shown that a high intake of omega-6 fats may contribute to immune dysfunction and increase the risk of certain diseases, such as asthma and allergic rhinitis. （19, 21）
however, the relationship between omega-6 fats and the immune response is complex and requires more human studies. （22）
regardless, researchers recommend that you maintain a healthy balance of omega-6 to omega-3 fats, which is thought to be approximately 1:1 to 4:1 to promote overall health (3).
this means eating more omega-3-rich foods — such as salmon, mackerel, sardines, walnuts, and chia seeds — and eating less omega-6-rich foods such as sunflower oil, corn oil, and soybean oil.
summary: eating more omega-3-rich foods and eating fewer omega-6-rich foods may promote optimal immune function.
4. Fried food
Fried foods are rich in a group of molecules called late glycosylation end products (AGEs). During high-temperature cooking, such as frying, AEG is formed when sugar reacts with protein or fat.
If levels of AGEs in your body become too high, AGEs can cause inflammation and cell damage (23).
AGEs are thought to weaken the immune system in several ways, including promoting inflammation, depleting the body's antioxidant mechanisms, inducing cellular dysfunction, and negatively affecting gut bacteria. （24, 25, 26）。
Therefore, the researchers believe that a diet high in AGEs may increase susceptibility to diseases such as malaria and increase the risk of developing diseases such as metabolic syndrome, certain cancers, and heart disease. （27, 28, 29）。
Reducing fried foods such as french fries, chips, fried chicken, fried steak, fried bacon, and fried fish will reduce your intake of AGEs (23).
Summary: Fried foods are bad for overall health and may cause immune dysfunction. The AGEs in fried foods are high and should be restricted to any healthy diet.
5. processed and charred meat
As with fried foods, processed and charred meats are also high in AGEs.
For example, a study analyzing AGE levels in 549 foods found that fried bacon, roasted hot dogs, roasted chicken thigh skin, and grilled steaks had the highest AGE content (23).
processed meats are also high in saturated fat. some studies have shown that diets high in saturated and low in unsaturated fats may contribute to immune system dysfunction. （19）。
in addition, a diet high in saturated fat may cause systemic inflammation and impair immune function (30, 31, 32).
in addition, a large intake of processed and charred meat has been linked to various diseases, including colon cancer. （33, 34）。
summary: diets with highly processed and high-temperature cooked meats are associated with an increased risk of disease and can damage your immune system.
6. Fast food
fast food has been linked to many negative health outcomes. eating too often can also damage your immune system.
a diet rich in fast food and highly processed foods can trigger inflammation, increase intestinal permeability, and lead to an imbalance of gut bacteria, all of which can negatively impact your immune health. （35）。
Fast food may also contain the chemicals bis(2-Ethylhexyl) phthalate (DEHP) and diisononyl phthalate (DiNP), which are two phthalates. Phthalates can seep into fast food, for example through packaging or plastic gloves worn when preparing food (36).
phthalates are known to disrupt your body's endocrine or hormone-producing systems. they may also increase the production of inflammatory proteins, which weaken your immune response to pathogens and lead to immune dysregulation. （37, 38, 39）。
in addition, phthalates may reduce the diversity of gut bacteria, which can negatively affect your immune system (38, 40).
summary: try to eat as little fast food as possible. eating too much carries health risks and can damage your immune system.
7. foods that contain certain additives
many foods, especially ultra-processed foods, contain additives to extend shelf life, texture, and taste. some of these may hurt your immune response.
for example, some emulsifiers added to processed foods to improve texture and shelf life can alter gut bacteria, damage the lining of the gut, and induce inflammation, all of which can lead to immune dysfunction. （41）
Carboxymethyl cellulose (CMC) and polysorbate 80 (P80) are commonly used emulsifiers associated with immune dysfunction in rodent studies. （42, 43）
similarly, human and animal studies have shown that the common additive carrageenan may induce intestinal inflammation and suppress the immune response, although more research is needed to better understand these effects. （44, 45, 46, 47, 48, 49）。
finally, corn syrup, salt, artificial sweeteners, and natural food additive citrates may also negatively affect your immune system (41).
summary: ultra-processed foods contain additives that may affect immune function, such as emulsifiers, thickeners, and sweeteners.
8. highly refined carbohydrates
regularly eating highly refined carbohydrates, such as white bread and sugary baked goods, can damage your immune system.
These are types of foods that are highly glycemic and cause your blood sugar and insulin levels to spike, which can lead to increased production of free radicals and inflammatory proteins such as CRP. （3, 4）
in addition, a diet rich in refined carbohydrates may alter gut bacteria, which can negatively affect your immune system (5, 50).
choosing nutrient-rich sources of high-fiber carbohydrates, such as starchy vegetables, oats, fruits, and legumes, rather than refined carbohydrates, can help support immune health.
summary: a diet rich in refined carbohydrates may adversely affect your immune system. choosing more nutritious carbohydrate sources, such as fruits and starchy vegetables, is a better choice for your overall health.
9. Certain high-fat foods
diets high in saturated fat and low in unsaturated fat are associated with immune dysfunction.
high saturated fat intake can activate certain signaling pathways that induce inflammation, thereby inhibiting immune function. a high-fat diet may also increase your susceptibility to infections by suppressing your immune system and white blood cell function (51, 52).
in addition, rodent studies have shown that a high-fat diet can cause changes in gut bacteria and damage the lining of the intestine, potentially increasing the risk of infection and disease. （53, 54）
researchers are still studying how different fatty acids affect the immune system, and more human research is needed.
that said, eating a balanced diet rich in fiber and a source of healthy fats may be a great way to support immune health.
summary: eating a diet high in saturated fat may impair immune function. following a balanced, high-fiber diet may be a great way to support immune health.
10. Artificially sweetened food and beverages
some artificial sweeteners have been linked to altered intestinal bacterial composition, increased inflammation in the intestine, and sluggish immune response. （55, 56, 57）。
there is growing evidence that artificial sweeteners, including sucralose and saccharin, may cause imbalances in gut bacteria. some researchers hypothesized that excessive use of artificial sweeteners may be harmful to immune health (40, 58, 59).
in addition, some studies of rodents and limited human case studies have also shown that heavy intake of artificial sweeteners may contribute to the progression of autoimmune diseases. however, more research is needed (60, 61).
that said, not all studies are consistent, and some have shown that moderate daily intake of sweeteners does not cause changes in gut bacteria or immune function (62, 63).
summary: artificial sweeteners have been linked to alterations in gut bacteria, which can impair immune function. in addition, some studies have shown that high intake may contribute to the progression of autoimmune diseases.
long story short
you can support your immune system with a healthy lifestyle.
this means limiting foods and beverages, processed meats, and fried foods that are high in added sugar and salt, all of which can adversely affect your body's immune function.
to support your immune system, it's best to follow a balanced diet rich in whole, nutrient-rich foods and limit your intake of ultra-processed foods as much as possible.