The 5 Foods Destroying Your Immune System

Chronic ConditionsBrain HealthMetabolic Health

Feb 15

Estimated Read Time: 7 minutes

When most people think about immune health, they think about vitamins, supplements, or the latest superfoods. What they rarely consider is how everyday foods can weaken their defenses long before symptoms appear.

The immune system isn’t just something that switches on when you catch a cold. It’s a constant, living network that depends on stable blood sugar, a healthy gut, balanced inflammation, and clean inputs. When those foundations are compromised, immunity weakens—making the body more vulnerable to infections, chronic inflammation, autoimmunity, and slow recovery.

Scripture reminds us that the body is a temple, not a dumping ground. What we consume either strengthens our defenses or erodes them over time.

Below are five of the most common foods and food groups to avoid. This article explains how they work against the body, where they’re found, and—most importantly—what to eat instead.

5 of the Worst Foods for Your Immune System

Americans now consume about 55% of their daily calories from ultra-processed foods, meaning more than half of what most of us eat each day comes from products high in added sugars, unhealthy fats, sodium, and industrial ingredients rather than whole, nutrient-dense foods. Among children and teens, this number is even higher—nearly 62% of daily calories from ultra-processed items.

Let's take a closer look at…

1. Sugar (Especially Processed Sugar and High-Fructose Corn Syrup)

If there's one substance that has done more damage to immune health than any other in the modern world, it's likely sugar.

While small amounts of natural sugars from whole foods like fruit are not inherently harmful, processed sugars overwhelm the immune system in multiple ways, especially when consumed daily. Even a single high-sugar meal can reduce immune cell effectiveness for several hours afterward.

High sugar intake has been shown to:

Blunt white blood cell activity, which reduces their ability to engulf and destroy pathogens
Increase systemic inflammation by activating inflammatory cytokines
Disrupt blood sugar balance, which stresses the adrenal glands and immune signaling
Feed harmful gut microbes and yeast, weakening gut-based immunity

Why High-Fructose Corn Syrup (HFCS) Is Worse:

HFCS deserves special mention because, unlike glucose, fructose is processed almost entirely in the liver.

The metabolic impact of excess HCS consumption creates an environment where inflammation thrives and immune resilience declines. Recent research shows:

High fructose consumption raises uric acid levels, which is linked to inflammation, elevated blood pressure, and insulin resistance
People consuming high levels of added sugars, which can include HFCS, have an estimated 3-fold greater risk of dying from heart disease, independent of weight or other risk factors

Where It’s Found (Foods to Avoid):

Soda, fruit juices, and sweetened beverages
Candy, pastries, and desserts
Breakfast cereals and granola bars
Condiments like ketchup, BBQ sauce, and salad dressings
Even “healthy” snacks marketed as low-fat or energy-boosting

What to Eat Instead:

In the best-case scenario, you'd only consume sugar from whole fruits, including the skins, which have their fiber intact and plenty of antioxidants.

Raw honey or pure maple syrup in moderation are healthier ways to sweeten recipes. Dates or fruit-based sweeteners used sparingly can also be useful.

To kick sugar cravings and your reliance on sweets, focus on protein, healthy fats, and fiber, which together make you feel more satiated, stabilize blood sugar, and contribute to metabolic health.ndrial function, DNA repair, and cellular longevity.

Here’s where things get interesting.

Nicotine’s molecular name shares a root with niacin (or vitamin B3) and nicotinamide. Both of these are nutrients the body uses to build NAD⁺. It's possible that nicotine might also mildly influence NAD⁺ metabolism or redox signaling.

But this does not mean nicotine is the best, or even a necessary, way to raise NAD⁺.

In fact, the body already has built-in, nutrient-based pathways for restoring NAD⁺ levels after illness or stress. These pathways are supported by real food, key vitamins like B3, adequate sunlight, restorative sleep, and compounds that nourish the mitochondria rather than stimulate the nervous system.

Nicotine may signal energy pathways, but B3-based nutrients help to rebuild them. When these foundations are in place, the body can rebuild cellular energy and resilience without relying on synthetic stimulants.

2. Artificial Sweeteners and Sugar Alcohols

Artificial sweeteners and sugar alcohols are often marketed as “better for you,” but many of them worsen gut health and immune function just as much as sugar itself.

The reason? These sweeteners can alter gut microbial diversity, and the majority of the immune system resides in the gut. When the microbiome is disrupted, immune regulation goes out of balance.

Artificial sweeteners have been shown to:

Reduce beneficial bacteria
Increase gut permeability (“leaky gut”), allowing inflammatory compounds into circulation
Disrupt glucose metabolism and insulin signaling

Sugar alcohols like erythritol, sorbitol, and maltitol are not much better:

Sugar alcohols—especially erythritol, sorbitol, and maltitol—are unfortunately not much better. They’re notorious for causing bloating, gas, and diarrhea in many people due to how they ferment improperly in the gut. They can also promote overgrowth of microbial species linked to inflammation and immune dysregulation.

One study found that despite not contributing calories or sugar to people's diets, artificial sweeteners altered the gut microbiome in ways that induced glucose intolerance or resistance, even in healthy volunteers.

People consuming high levels of artificial sweeteners have been shown to have higher levels of inflammatory markers, independent of calorie intake—not to mention they often cause digestive issues like diarrhea.

Where They’re Found:

Diet sodas and “zero-calorie” drinks
Sugar-free gum and candy
Keto and low-carb snacks
Protein bars and shakes
Many “diabetic-friendly” foods

Better Sweetening Options:

Raw honey, which is naturally antimicrobial and enzyme-rich
Pure maple syrup (in small amounts), which contains minerals and antioxidants
Monk fruit, a zero-calorie option that does not disrupt gut bacteria. Just avoid erythritol and heavily processed blends whenever possible.

3. Dairy Containing A1 Beta-Casein

For many people, A1 dairy can potentially be even more inflammatory than gluten due to its impact on gut health. The main reason is that A1 beta-casein breaks down into a peptide called beta-casomorphin-7 (BCM-7) during digestion, which can bind to opioid receptors in the gut and nervous system.

BCM-7 in conventional dairy has been linked to:

Increased gut permeability, a precursor to immune activation and systemic inflammation
Activation of immune pathways associated with autoimmune responses
Symptoms, including GI distress, breakouts, and brain fog, in sensitive individuals

When the gut barrier is compromised, the immune system is constantly triggered. That’s why dairy consumption is often linked to GI distress, immune activation, and symptoms like breakouts and brain fog.

On the other hand, many people who think they “can’t tolerate dairy” actually can tolerate A2 dairy just fine—only they may have never had the chance to test this. That’s because their symptoms are not always caused by lactose intolerance or fat in dairy, but by the inflammatory peptide BCM-7.

For example, research shows populations consuming mostly A2 dairy (such as from goats or sheep) tend to have lower rates of inflammatory bowel symptoms compared to typical Western dairy consumers.

Where A1 Dairy Is Found:

Most conventional cow’s milk
Standard cheeses, yogurts, and ice cream
Dairy from Holstein cows (the most common breed in the U.S.)

Better Dairy Options:

A2 dairy from A2 cows, goats, or sheep
Raw dairy (where safely sourced), which you can find at farmers' markets and online
Grass-fed, organic dairy products
Ghee or butter, which have minimal casein and lactose

4. Shellfish (Biblically “Unclean” Foods)

Shellfish—including shrimp, crab, lobster, oysters, and clams—are encouraged by many dieticians and mainstream health, yet both Scripture and science give us reasons to be cautious about eating seafood "without fins and scales." In Leviticus, shellfish are considered unclean—and while this classification is spiritual, it also aligns with recent observations about contamination and disease risk.

Shellfish are bottom feeders and filter feeders, which means they:

Accumulate heavy metals like mercury, cadmium, and arsenic
Harbor bacteria and parasites more easily
Spoil quickly and are a common source of food poisoning

In many cases, digestive distress and immune activation can follow shellfish consumption, and the more often you eat it, the more likely you are to run into problems.

Studies show that a single serving of contaminated shellfish can trigger immune activation and oxidative stress. Mercury and arsenic, sometimes found in shellfish, are known to suppress immune cell activity and promote chronic inflammation.

Shellfish I Recommend Avoiding:

Shrimp, crab, lobster
Oysters, clams, mussels
Shellfish-based broths and sauces

Cleaner Protein Alternatives:

Wild-caught fish with fins and scales (like wild-caught salmon or sardines)
Pasture-raised poultry
Grass-fed beef and lamb
Organ meats (liver, heart) for immune-supportive nutrients

5. Seed Oils (Unstable Polyunsaturated Fats)

Seed oils are one of the most destructive modern additions to the food supply, including for immune health.

Soybean, safflower, sunflower, and other refined seed oils are high in omega-6 polyunsaturated fats, which:

Are chemically unstable and can become oxidized easily
Promote chronic inflammation when consumed in excess, which many Americans do
Damage cell membranes and mitochondria
Disrupt immune signaling and weaken immune resilience.

Some studies have linked high seed oil intake to metabolic dysfunction, cardiovascular issues, and immune imbalance, and many studies show more favorable effects when people consume fats like olive oil instead of more processed vegetable oils.

Types of Seed Oils to Avoid Include:

Soybean oil
Corn oil
Canola oil
Sunflower and safflower oil
Grapeseed oil

Where They’re Found:

Fast food
Processed snacks, like chips, cookies, popcorn, etc.
Salad dressings and condiments like mayonnaise
Restaurant cooking oils

What to Use Instead:

Extra-virgin olive oil, which is anti-inflammatory and rich in polyphenols (if it has a bitter taste, this is a good indication it's high in protective nutrients)
Avocado oil, which is stable at higher heat and great for cooking
Coconut oil, which supports immune and metabolic health
Grass-fed butter or ghee
Beef tallow and animal fats that were used traditionally

Key Takeaways on the Worst & Best Foods for Your Immune System

Sugar suppresses immune defenses and fuels inflammation
Artificial sweeteners affect the gut microbiome, where most of your immune system lives
A1 dairy can trigger immune and digestive reactions
Shellfish often carry contaminants (like metals and bacteria) that stress the immune system
Seed oils drive chronic inflammation and immune dysfunction
Focus instead on natural, whole foods like grass-fed meat, virgin olive oil, whole fruit with skins, leafy greens, avocado, wild fish, eggs, and raw A2 milk.

References:

https://www.cdc.gov/nchs/products/databriefs/db536.htm

https://pubmed.ncbi.nlm.nih.gov/32395846/

https://pubmed.ncbi.nlm.nih.gov/36198287/

https://pmc.ncbi.nlm.nih.gov/articles/PMC9471313/

https://pmc.ncbi.nlm.nih.gov/articles/PMC9960726/

https://pubmed.ncbi.nlm.nih.gov/26586275/

https://pmc.ncbi.nlm.nih.gov/articles/PMC10144565/

https://pmc.ncbi.nlm.nih.gov/articles/PMC11501561/

https://www.mdpi.com/2072-6643/13/6/2029

https://pmc.ncbi.nlm.nih.gov/articles/PMC7014832/

https://pmc.ncbi.nlm.nih.gov/articles/PMC10486734/