What you eat on a daily basis can have a dramatic effect on your immune system’s ability to do its job and keep you healthy. Making just a few dietary changes can significantly improve your health and strengthen your immune system.

Research has long shown that nutrition plays an important role in our immune health. Certain foods have consistently been shown to weaken a person’s immune response, making them more susceptible to infection and slowing down the healing process. Conversely, other foods have been shown to strengthen our immune response, making it less likely we become sick.

Foods that Weaken the Immune System

“Everything in moderation” is a common refrain you often hear when someone wants to justify eating something that they know is not healthy, but they want to eat it anyway. And many times, eating something on occasion – let’s say at a birthday party or other yearly celebration – that isn’t healthy but provides a great sense of pleasure or satisfaction – like a piece of cheesecake or bowl of ice cream – probably doesn’t do any long-term harm. However, there are certain foods (or food ingredients), that have consistently been shown to depress immune function. This effect may last for a few hours to a few days after consumption, no matter how often you eat them. Naturally, the more often you eat them, the greater the effect on the immune system, which can significantly decrease your body’s ability to fight off infection over time.

Here are the foods to avoid in order to optimize immune health:

Foods High in Sugar

Research has consistently shown that foods high in sugar – whether that is sucrose, glucose, high fructose corn syrup, organic cane sugar or beet sugar or any other source – consistently and reproducibly depresses immune function, and this effect can last from hours to days after consumption. Eat foods that are high in sugar (or simple carbohydrates) too often, and you will significantly increase your risk of infection.

Foods high in sugar or simple carbohydrates include:

  • Soda, fruit juices and energy drinks
  • Candy, chocolate and sweets
  • Cakes and cookies
  • Baked goods, including muffins, breads and pastries
  • Sugary breakfast cereals and bars
  • Sweetened and flavored dairy products, including ice cream, sweetened yogurt and chocolate milk

Alcoholic Beverages

Many alcoholic beverages present a particularly nasty combination of immune-suppressing ingredients because they are often loaded with sugar, increase consumption of unhealthy foods and displace healthier foods and drinks from the diet. Not only that, alcohol contains more calories (7 kcal/gram) than either carbohydrates or protein (4 kcal/gram), and almost no beneficial vitamins and minerals to help properly use those calories. This robs the body of these vital nutrients, putting further strain on proper immune function.

Be honest – when was the last time you reached for a salad or steamed vegetables after having a few drinks? It’s much more likely that you reach for some rich and savory foods – commonly referred to as comfort foods – and that you eat more than you would normally, as alcohol stimulates the appetite and depresses your ability to recognize when you’ve eaten enough. This is all to say: go go easy on the alcohol to improve your immunity.

Processed Foods

Processed foods often contain unhealthy fats, sugars and additives designed to improve taste, texture (mouth feel) and shelf life; unfortunately, this combination of anti-nutrients has the undesirable effect of weakening the immune system.

Processed foods include almost anything in a bag, box or package that can sit on the shelf for an extended period of time without spoiling.

Typical offends include:

  • Fast food – anything that can be served to you through a window or a drive through
  • Microwave meals
  • Cookies, cakes, crackers and breads
  • Soda and sweetened beverages
  • Chips, crisps and salty/sweet snacks
  • Processed meats, including bacon, hot dogs, salami, deli meats, sausage and ham

Foods that Strengthen the Immune System

The good news is that there are loads of healthy foods that have been shown to improve and strengthen immune function. Basically, any deep-colored vegetable or fruit will contain vitamins, minerals and/or phytonutrients that can help the body and immune system perform at it’s best.

In particular several foods can super-charge the immune system:

Cruciferous Vegetables

Cruciferous vegetables – including broccoli, Brussel sprouts, cauliflower, cabbage and kale – are packed with compounds that are good for just about every aspect of your health. In particular, broccoli and broccoli sprouts are good sources of a sulfur compound called sulforaphane that may help boost the immune system.

Studies have also found that sulforaphane can have anti-inflammatory, antioxidant and anti-cancer properties, so be sure and eat a serving or two or broccoli several times weekly.

Foods that Contain Zinc

Research has clearly shown that zinc is essential to the proper functioning of the immune system and most people don’t get enough of it, leading to sub-optimal immune function.

Good sources of zinc include:

  • oysters
  • pumpkin seeds
  • beef
  • baked beans
  • chicken breast
  • peas

Citrus Fruits

Citrus fruits contain ample amounts of vitamin C and bioflavonoids that have been consistently shown to improve many facets of the system.

Vitamin C contributes to immune defenses by supporting various cellular functions of both the innate and adaptive immune system. Vitamin C supports epithelial barrier function (in the skin, GI tract, respiratory tract and urinary tract) against pathogens and promotes the free-radical scavenging activity of the skin, thereby potentially protecting against environmental oxidative stress.

Vitamin C also accumulates in specific immune cells, such as neutrophils and lymphocytes, and can enhance  their ability to fight and kill bacteria and viruses.

Conversely, Vitamin C deficiency results in impaired immunity and higher susceptibility to infections. In turn, infections significantly lower vitamin C levels in the body and supplementation with vitamin C appears to be able to both prevent and treat respiratory and systemic infections.

Prophylactic prevention of infection requires dietary vitamin C intakes that provide at least adequate, if not saturating plasma levels (i.e., 100–200 mg/day), which optimize cell and tissue levels; this can certainly be accomplished with a healthy diet. In contrast, treatment of established infections requires significantly higher (1-6 gram) doses of the vitamin to compensate for the increased inflammatory response and metabolic demand.

Eating citrus fruits, deep colored berries and cruciferous vegetables daily is a great way to meet the average daily requirements, while supplemental vitamin C can be used to meet acute and/or chronic needs.


The benefits of garlic on human health have been proclaimed for centuries; however, only recently have Allium sativum and its derivatives been proposed as promising candidates for maintaining and enhancing the immune system.

Garlic appears to enhance the functioning of the immune system by stimulating certain cell types – such as macrophages, lymphocytes, natural killer (NK) cells, dendritic cells, and eosinophils – making it easier for them to identify, target and eliminate foreign invaders.

Garlic has also shown a remarkable ability to reduce inflammation, prevent cancer and protect us from a variety of disorders ranging from cardiovascular disease to diabetes and obesity.

Eat garlic any way that you can – raw, baked, sautéed or as an infused oil – it’s likely to be the single best thing you can do for your health.


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