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The Effects of Sugar on The Immune System
April 18, 2020
Image by Myriam Zilles from Pixabay

While a spoonful of sugar may help the medicine go down, the real medicine for our bodies seems to be forgoing that spoonful of sugar (and most other spoonfuls) altogether. We’re going to look at the effects of sugar on the immune system in this article.

In nutritional terms, our food is composed of three things: carbohydrates, proteins and fats. Carbohydrates, including fiber, starches and sugars, provide cellular energy when metabolized and fiber is essential for a healthy digestive system.

However, the Standard American Diet (SAD) contains excessive amounts of sugar, and this excess glucose is stored in the liver, muscles and other cells, or is converted to fat. This, in turn, has been shown to have a number of negative effects on the immune system and our bodies in general.

Let’s take a look at how sugar has the potential to disrupt the immune system. 

The Spoonfuls Add Up

Before we dive into the science, let’s consider sugar consumption on the whole. Fruits and vegetables contain natural sugars, starch and fiber, and when included in a balanced diet, make up all the carbohydrates your body requires, and possibly even more than what is needed for natural metabolic processes. Foods containing added sugars will almost always result in consuming excess sugar to what the body needs. Refined grains, like bread and pasta, soft drinks, candy and even added table sugar makes it easy to consume more sugar than the body requires. 

The Harvard School of Public Health highlights that it’s important to keep in mind that on nutrition labels, 4 grams of sugar is equal to 1 teaspoon of sugar! And, it’s estimated that Americans consume 22 teaspoons of added sugar every day. (1)

Sugar and the Immune System

Even as far back as the early 1970s, a study determined that sugar had negative effects on the immune system. The study wanted to see how sugars impacted the ability of the human immune system to attack and consume pathogens, such as bacteria and viruses. Testing a wide variety of simple sugars, researchers determined that all tested sugars significantly reduced the ability of human neutrophils, a type of white blood cell, to engulf pathogens, and this decreased capacity remained for up to five hours after the sugar was consumed. (2)

As research is expanding with respect to the complexity of the immune system and how nutrition affects it, even more is being uncovered about the harmful effects of sugar.

Systemic Inflammation

According to a 2018 meta-analysis of previous sugar studies, dietary sugar intake (particularly from sugar-sweetened soft drinks and beverages), may stimulate subclinical widespread inflammation in the body. It has been shown that C-reactive protein (CRP), an inflammatory marker, is higher in those who consume higher amounts of dietary sugar and soft drinks. (6)

Read more about Managing Inflammation Through Diet

What is it that causes this increase in inflammation? The immune system is a very complex system of cells, and while the mechanisms behind what causes inflammation are not exactly clear, one theory stems from lipotoxicity. Eating (or drinking) too much dietary sugar promotes the formation of free fatty acids (FFA) in the liver, and the metabolites from FFA, trigger an inflammatory response in the immune system that leads to an attack on healthy cells in various body systems. This systemic inflammation may be responsible for many chronic illness, including autoimmune conditions, cardiovascular disease, diabetes, dementia and neurodegenerative disease, depression and mental health issues. (6)

Image by Tania Dimas from Pixabay

Obesity and Immune Dysfunction

Not all of the effects of sugar on the immune system are direct. While excess sugar seems to cause low-level inflammation even in individuals who are at a healthy weight, changes in eating habits have led to record levels of obesity in both the American and global populations, which has created a number of particular health challenges, including an increase in the incidence of insulin resistance, type 2 diabetes, and cardiovascular diseases. 

To think of the problem in another way, let’s consider that obesity is due to an excess of energy storage caused by eating energy-dense, nutrient-poor foods, including excessive amounts of sugar and other high-sugar processed foods and beverages. 

This excess of sugar, or energy, cannot be used because it is not required by the body. Energy that cannot be expended by the body, must be stored in body cells or stored as fat. This overabundance of glucose contributes to a number of problems seen in obesity-related metabolic disorders, including substantial alterations in immune responsiveness. Obesity leads to an imbalance of the cytokine network which produces a low-grade systemic inflammatory response and an elevation of inflammatory cytokines throughout the body. (4)

In addition to cytokine disruption, obesity has been linked to:

  • Macrophage accumulation in fat tissue, leading to both phagocytic impairment and associated inflammation (5)
  • An increased susceptibility to systemic infections and infectious complications after surgery
  • Higher incidence of skin and respiratory tract infections (6)

In short, inflammation and immune cell impairment seen in obese individuals are significantly due to the overconsumption of sugar and the body’s inability to use that excess energy.

Gut Dysbiosis

Along with systemic inflammation and the unique challenges of obesity, sugar also plays a role in creating gut dysbiosis which has a significant impact on the immune system. Diets high in fat and sugar have been shown to lead to changes in the microbiota of the gut. Changes and imbalances in the microbial community of the gut leads to intestinal permeability, which allows food particles that have not been fully digested to enter the bloodstream. This is turn can cause everything from inflammation, insulin resistance, glucose intolerance and metabolic diseases. Also known as leaky gut syndrome, it has been shown to play a role in increased levels of inflammatory biomarkers and cytokines, including tumor necrosis factor. (7)

Read more about Digestive Dysfunction: The Long-Term Impact

Finding the Sweet Spot of Health

Looking at sugar with respect to the immune system, you may have picked up on just how much everything is interconnected. Consuming sugar in excess to what your body needs is very easy to do, particularly with sugary beverages, and convenience, processed and fast foods. This excessive sugar causes a cascading effect that leads to poor health by upsetting the natural balance of the immune system. Systemic inflammation, obesity and gut dysbiosis are all linked in numerous ways, and dietary sugar plays an important, yet sinister, role in all of it. (8)

While many of us have a complicated relationship with food, whether it’s due to societal or personal pressures, our emotions, or any number of other factors, the most important thing to focus on is that we all have the power to change. Boiling it down to the science of nutrition and looking at how your body actually fuels itself can offer a new perspective on what your body really needs. Instead of thinking about restricting sugar, focus on adding in more healthful options. These additions can help you to slowly phase out those less healthy options, and any steps to reduce sugar in your diet are bound to pay off in the long run!

You may be interested in The Role of Vitamin D in Autoimmune Disease


1. Harvard T.H. Chan School of Public Health. The Nutrition Source: Added Sugar in the Diet [Internet]. [cited 10th January 2020]. Available from:

2. Sanchez A, Reeser J, Lau H, Yahiku P, Willard R, McMillan P, et al. Role of sugars in human neutrophilic phagocytosis. Am J Clin Nutr. 1973;26:1180-4. 

3. Della Corte K, Perrar I, Penczynski K, Schwingshackl L, Herder C, Buyken A. Effect of Dietary Sugar Intake on Biomarkers of Subclinical Inflammation: A Systematic Review and Meta-Analysis of Intervention Studies. Nutrients. 2018;10:606. 

4. Aronson D, Bartha P, Zinder O, Kerner A, Markiewicz W, Avizohar O, et al. Obesity is the major determinant of elevated C-reactive protein in subjects with the metabolic syndrome. Int J Obes. 2004;28:674–9.

5. Neels J, Olefsky J. Inflamed fat: what starts the fire? J Clin Invest. 2006;116:33-5.

6. Wolowczuk I, Verwaerde C, Viltart O, Delanoye A, Delacre M, Pot B, et al. Feeding our immune system: impact on metabolism. Clin Dev Immunol. 2008:639803.

7. Do M, Lee E, Oh M, Kim Y, Park HY. High-Glucose or -Fructose Diet Cause Changes of the Gut Microbiota and Metabolic Disorders in Mice without Body Weight Change. Nutrients. 2018;10:761.

8. Brown K, DeCoffe D, Molcan E, Gibson DL. Diet-induced dysbiosis of the intestinal microbiota and the effects on immunity and disease. Nutrients. 2012;4:1095-119.


About author

Heather Cooan

Heather is a marketing executive turned nutrition consultant and educator. Heather advocates for informed consent, bodily autonomy, and healthcare authorship. She speaks and writes on nutrition and lifestyle design interventions for health recovery. Heather successfully recovered her health from vulvar cancer, Hashimoto's, and lichen sclerosus. She reversed estrogen dominance, insulin resistance, arteriosclerosis, and fatty liver utilizing a food-as-medicine and integrated clinical treatment approach. Heather is a certified Functional Diagnostic Nutrition® Practitioner and Nutrition Therapy Practitioner.

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