7 Worst Foods For Your Immune System, According To A Dietitian

Like a superhero clad in a cape, your immune system constantly monitors evil threats such as viruses or bacteria and kicks into action when you get sick. After the COVID-19 pandemic, keeping your immune system fit to fight off the next virus could be a priority. While no specific food or supplement can guarantee you’ll never get sick, your overall diet can play an important role in supporting the work your immune system does to ward off unwanted infections.

Eating a diet rich in fiber and healthy fats and providing sufficient amounts of key nutrients, such as vitamins A, E, C, D, zinc and iron can optimally support the immune system. However, a diet lacking in these nutrients and high in added sugars and saturated fats could weaken the immune system.

To give your immune system all the support it needs to keep you from getting sick, here are 7 foods you should limit.

1. Refined grains

Since most of the immune cells are found within the lymphoid tissue that lines the gut, it’s important to limit refined carbohydrates, which are generally higher in sugar and stripped of the fiber that allows a healthy gut to thrive. According to a 2022 research published in Allergydietary fiber supports the immune system in a couple of different ways.

First, a healthy intestinal barrier serves as your primary defense mechanism against the bacteria and viruses found in the food you eat. Second, intestinal bacteria produce short-chain fatty acids (SCFAs) by fermenting the fiber in the food. These SCFAs help regulate the function of your immune cells so they perform optimally when introduced to a viral or bacterial threat.

2. Alcohol

Alcohol is also not the best for your gut which plays a vital role in immunity. A 2021 review in Toxicological reports noted that alcohol could affect the diversity of healthy bacteria in the gut and contribute to a less functional gut barrier, meaning pathogens can get past it. Excessive alcohol intake can also inhibit the adaptive immune system’s ability to create the antibodies needed to ward off foreign invaders such as the flu virus.

Alcohol can also keep you from getting good sleep, which is essential for your immune system to be in tip-top shape. If you like to drink occasionally, do it in moderation: two standard drinks or less per day for men and one or less per day for women, according to the CDC.

3. Sugary drinks

We know that too much added sugar is bad for you. Excessive sugar intake, especially through sugary drinks, can negatively affect the body and contribute to a weakened immune system. According to a review from 2022 in Human immunologyExcess fructose (a type of sugar) intake alters the composition of the gut microbiota so that beneficial strains of bacteria have a harder time thriving. High blood sugar levels can also alter the permeability of the intestines, contributing to chronic inflammation. Although inflammation is a normal step in the body’s innate immune response, chronic inflammation can leave your immune system too overloaded to ward off new infections.

4. Fried foods

Fried foods are richer in advanced glycation end products (AGEs). These compounds occur naturally during cooking, especially at high temperatures such as frying. Research, such as a 2020 article in Nutrientsfound that AGEs may be associated with a less optimal gut microbiome, increased inflammation and a weaker intestinal barrier which can affect the immune system.

5. Red meats and processed meats

While red meat may have a place in a healthy diet, excessive intake of red meat and processed meats like bacon and hot dogs can be bad news for your immune system. When red meat is digested, intestinal bacteria create a substance called trimethylamine (TMA) which is then transformed into trimethylamine N-oxide (TMAO) by the liver.

Some TMAOs are nothing to worry about, but higher TMAO levels are often associated with an unhealthy community of gut bacteria, as noted in this 2019 review in Nutrients. More TMAO-producing intestinal bacteria living in the gut are often related to chronic inflammation, which could lead to an overloaded immune system.

6. Caffeinated drinks

Coffee and tea are rich in antioxidants that can support a healthy immune system by reducing inflammation, but if they contain caffeine, they can interfere with sleep quality. As noted in a 2019 paper from Physiological reviewsNumerous research studies have linked sleep with immune function. So, if you like caffeinated drinks, limit them to just a couple cups a day and aim to consume them at least 6 hours before bedtime.

7. Salty foods

A 2018 review in Hypertension has linked a high sodium intake to increased inflammation, changes in the gut microbiome, and changes in the body’s adaptive immunity. However, initial clinical trials are small, so more research is needed to help us understand the relationship between salt intake and immunity.

However, most people generally eat far more salt than recommended. According to the FDA, Americans consume approximately 3400 mg of sodium per day. However, the 2020-2025 Dietary Guidelines for Americans recommend adults limit their sodium intake to less than 2300 mg per day or about 1 teaspoon of table salt. Consume sodium-rich foods such as fast foods, salty snacks, processed meats, and canned goods less often to reduce your overall salt intake.

Frequent questions

What are the best foods to eat for the immune system?

A 2019 review in Nutrients suggests following nutritious diets like the Mediterranean diet that includes foods high in fiber, omega-3 fatty acids, vitamins A, C, D and E, and zinc can best support a healthy immune system. We also know that staying hydrated and eating enough protein is important. Some foods to incorporate into your diet more often to support your immune system are whole grains, fruits and vegetables, nuts and seeds, legumes, lean meats, and fatty fish.

What foods can activate your immune system?

A diet high in ultra-processed foods, added sugars, sodium and saturated fats can increase chronic inflammation and reduce immune function, increasing your risk for health conditions like type 2 diabetes and heart disease.

What weakens your immune system the most?

Chronic undernutrition, dehydration and excessive alcohol consumption can weaken your immune system making you more susceptible to disease. Lifestyle factors such as stress and lack of sleep also impact the immune system. So when cold and flu season rolls around, make sure you’re not only eating a balanced diet, but also prioritizing sleep and stress-reducing strategies.

The bottom line

Give your immune system a fighting chance by supporting it with healthy meals packed with various nutrient-dense foods. Additionally, drinking plenty of fluids, ensuring adequate sleep, and reducing stress also help ensure proper immune function. And if you’re wondering which foods can weaken it, you can consider limiting the foods on this list but don’t worry too much about the occasional sweet, salty snack, or glass of wine.

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