- Short bursts of high fructose intake made key immune cells in healthy adults more sensitive to bacterial toxins and more likely to switch on inflammation.
- Fructose, but not glucose, increased Toll like receptor 2 on monocytes and boosted inflammatory messengers such as interleukin 6 and tumour necrosis factor alpha.
- The authors warn that the effect could be more harmful in people with conditions such as type 2 diabetes or fatty liver disease, where inflammation is already a problem.
A team at the University of Vienna wanted to know whether common sugars change the way our immune system responds to bacteria.
They focused on monocytes, a type of white blood cell that circulates in the blood and helps coordinate inflammation.
In two randomised studies, healthy adults drank beverages sweetened either with fructose, the sugar found in fruit, or with glucose.
The scientists then measured how their monocytes responded to lipoteichoic acid, a toxin from certain bacteria.
They also ran cell culture experiments with isolated monocytes to understand exactly what was happening inside the cells.
What they found
After fructose drinks, monocytes had more Toll like receptor 2 on their surface. This receptor recognises lipoteichoic acid and other bacterial components and acts as an on switch for inflammation.
Glucose drinks did not cause the same increase.
When exposed to lipoteichoic acid, monocytes from the fructose group released more inflammatory cytokines, including interleukin 6, interleukin 1 beta and tumour necrosis factor alpha.
The team showed that fructose reprogrammed cell metabolism towards glutaminolysis and oxidative pathways that fuel this heightened inflammatory response.
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In plain terms, fructose seemed to prime immune cells to overreact to bacterial toxins, which may do more harm than good if this response becomes chronic or excessive.
Why it matters for people with metabolic conditions
The volunteers in this study were healthy.
Even so, short term high fructose intake was enough to shift their immune cells into a more inflammatory state.
The authors say this raises concern for people who already live with conditions that involve chronic low grade inflammation, such as type 2 diabetes or metabolic associated fatty liver disease.
For now, the message is not that one glass of fruit juice will wreck your immune system.
Rather, it adds to the growing evidence that regular high intake of free fructose, especially from sugary drinks and sweets, can have subtle effects far beyond blood glucose, including on liver health, cancer risk and now the way immune cells respond to bacteria.
For people with diabetes, who already have higher risks of infection and liver problems, keeping fructose sweetened drinks as an occasional treat rather than a daily habit remains a sensible approach.
