Too Much Added Sugar May Affect Your Immune System, Study Suggests

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Key Takeaways

  • Many studies have linked fructose, a form of sugar found naturally in fruit and also in a wide range of processed foods and sugary drinks, with adverse health outcomes.
  • New research suggests that a diet high in fructose might interfere with healthy immune system function.
  • Experts say it's important to eat fruits as part of a healthy diet, but limit foods containing all added sugars—not just fructose.

Fructose has gotten a pretty bad rap in recent years, as research has shown repeatedly that high levels of this sugar can lead to various adverse health outcomes.

It’s been associated with obesity, Type 2 diabetes, and non-alcoholic fatty liver disease. And now a new study published in Nature Communication has suggested that a diet high in fructose could have some adverse effects on the immune system. 

That being said, it's important to keep in mind that fructose comes from multiple sources, some healthier than others. The fructose you get from fruits and some vegetables is a key part of a balanced diet, whereas high fructose corn syrup, a common added sugar, is not.

Sugar, Inflammation, and Your Immune System

In this particular study, Scientists from Swansea University, Wales, in collaboration with researchers from the University of Bristol and the Francis Crick Institute in London, focused on how human and mouse cells responded to fructose exposure. They discovered that the sugar causes the immune system to become inflamed, which in turn produces more reactive molecules associated with inflammation.

Inflammation of this kind can damage cells and tissues, and stop organs and body systems from working as they should. The study, published in the journal Nature Communications, warns that this could lead to disease.

As the authors write in their paper, “fructose reprograms cellular metabolic pathways to favor glutaminolysis and oxidative metabolism, which are required to support increased inflammatory cytokine production.”

What is Fructose? 

“Fructose is a monosaccharide (a single sugar) found in fruit,” says Vanessa Rissetto, MS, RD, CDN, co-founder of Culina Health. “Like other sugars, such as glucose, the body uses it for fuel.” 

But fruit isn’t the only source of fructose. It's also found in honey and in certain vegetables, like asparagus and squash. And as high fructose corn syrup (HFCS), a manufactured sweetener made from cornstarch, it’s widely used in food production, commonly in sugary drinks, sweets, and processed foods, as well as more unexpected places, like salad dressing and frozen pizza.

Vanessa Rissetto, MS, RD, CDN

Too much sugar of any kind can result in glucose control issues or impairment in the uptake of glucose into the body’s cells, which could possibly eventually lead to Type 2 diabetes.

— Vanessa Rissetto, MS, RD, CDN

It’s these manufactured forms of fructose that pose a potential health risk, experts warn. But the jury is still out on whether HFCS is more dangerous to your health than regular table sugar.

“Getting high amounts of fructose from whole fruits is difficult,” explains Tejal Pathak, RD, a clinical dietitian, diabetes educator, and practitioner based in Houston, Texas.

Pathak continues, “Moreover, whole fruits are rich in fiber, vitamins, minerals, and antioxidants, which are all essential for good health. Eating fruit every day helps you meet your daily requirement of nutrients like folate, fiber, vitamin C, and many more.”  

On the other hand, it’s easy to consume high quantities of HFCS and other types of added sugar in processed snacks and beverages. 

“When fructose is taken in small quantities, it is metabolized by the small intestine,” Pathak says. “However, when it’s consumed in higher quantities it’s not completely cleared by the small intestine and it reaches the liver and colonic microbiota for further metabolism, where it is then converted to fatty acids.” 

How to Reduce Your Added Sugar Intake 

According to the Dietary Guidelines for Americans, 2020-2025, sugar-sweetened beverages such as soda, sports drinks, energy drinks, fruit drinks, tea, and coffee, contribute over 40% of the daily intake of added sugars in adults. However, the guidelines don't single out high fructose corn syrup, instead recommending that people limit their consumption of all added sugars.

“Attempts should be made to limit calories from added sugars to less than 10% of your daily intake,” Pathak says. “This can be achieved by reading nutrition labels, avoiding packaged food products with added sugars, replacing sugary beverages with water or unsweetened beverages, choosing whole fruits, and consuming home-cooked meals.” 

Tejal Pathak, RD

Attempts should be made to limit calories from added sugars to less than 10% of your daily intake.

— Tejal Pathak, RD

When it comes to fruits, the health benefits are well-known, but it’s important to have a varied diet. 

“If you're only taking in fruits, then likely you're missing out on other nutrients and also important things for bodily function, such as protein and fat,” Rissetto says. “Too much sugar of any kind can result in glucose control issues or impairment in the uptake of glucose into the body’s cells, which could possibly eventually lead to Type 2 diabetes.” 

Because fruit contains sugar, Rissetto suggests pairing it with fat to slow down digestion. And if you have issues with blood sugar, make sure you adhere to recommended serving sizes. “For example, the serving size of grapes is 18, whereas the serving size of raspberries is 1 cup since it has more fiber (8g per cup),” Rissetto explains. 

What This Means For You

If you're concerned about the amount of added sugar in your diet, a good first step is cut back on the amount of sugar (of any kind) you add to things you eat or drink regularly, such as coffee, tea, cereal, and pancakes. Switch soda for water, and compare food labels and choose the product with the lowest amount of added sugar.

More tips are available on the American Heart Association website, or you could ask a registered dietitian to help you get on the right path. It can be daunting to overhaul your diet in a major way, so take it one step at a time—they all count.

3 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. DiNicolantonio J, Subramonian A, O’Keefe J. Added fructose as a principal driver of non-alcoholic fatty liver disease: a public health crisis. Open Heart. 2017 Oct. doi:10.1136/openhrt-2017-000631

  2. Jones N et al. Fructose reprogrammes glutamine-dependent oxidative metabolism to support LPS-induced inflammation. Nature Communications. 2021 Feb. doi:10.1038/s41467-021-21461-4

  3. US Department of Agriculture. Dietary Guidelines for Americans, 2020-2025. December 2020.

By Claire Gillespie
Claire Gillespie is a freelance writer specializing in mental health. She’s written for The Washington Post, Vice, Health, Women’s Health, SELF, The Huffington Post, and many more.