Sugar-Free Diets May Have a Hidden Side Effect, Study in Mice Suggests

Cutting down on sugar delivers a host of health benefits, from minimizing tooth decay to improving mental health.

A new study in mice flies in the face of that research, suggesting that a sugar-free diet might have some unintended side effects.

Most studies to date have examined the drawbacks of too much sugar, which includes a long list of chronic diseases, such as diabetes.

Sugar is a source of energy for us and the bacteria that live in our guts, but it's not necessarily a good one.

The sugar added to many foods and drinks is highly processed, so it's absorbed into the bloodstream quickly – much faster than other, more complex carbohydrates – giving you a sugar hit that keeps you eating more.

But what happens without it?

In this latest study, 12 mice were put on low-fat diets – either with or without sucrose, a common form of sugar (which might be in your kitchen cupboard).

"Low-fat diets are widely promoted as health-protective," the researchers from the Dasman Diabetes Institute in Kuwait explain in their study abstract.

"However, the consequences of removing sucrose within a low-fat dietary framework remain unclear."

In their study, the researchers found that the zero-sugar mice experienced numerous negative health effects across the course of 16 weeks, compared to the other group.

A disruption of gut bacteria was one of the changes observed in the zero-sugar mice; these animals had fewer helpful strains and more inflammatory ones at the end of the study.

It's well established that the foods we eat shape the vast communities of microbes that live inside our intestines, but the gut microbiome is exactly that: vast and dynamic.

So we can't really say what these changes mean, especially not for humans and when we don't even know what a healthy gut microbiome looks like, from person to person.

Until the work is published in a peer-reviewed journal, we also don't know much about how the study was conducted, such as what the animals' diets contained.

However, the researchers say their findings highlight the importance of maintaining a healthy gut microbiome through diet, rather than focusing only on sugar restriction.

"The findings suggest that complete removal of sucrose from a low-fat diet may negatively affect gut microbiota and metabolic health," says immunologist Rasheed Ahmad from the Dasman Diabetes Institute.

"The study highlights the importance of maintaining balanced dietary carbohydrates to support gut and immune homeostasis."

Many diets involve cutting out excess sugar. (Rod Long/Unsplash)

Other negative health effects associated with consuming no sugar included impaired glucose control (meaning blood sugar was less well regulated) and signs of insulin resistance (which results in excess sugar in the bloodstream), both of which are linked to type 2 diabetes.

The researchers also spotted fat building up in the livers of the zero-sugar mice, even though their body weights were about the same as the sugar-eating group.

We're still at the early stages of analyzing these findings, but this delicate balance of gut bacteria and blood sugar levels seems to be impacted when sucrose isn't available.

Given that past studies have shown how reducing added sugar can lead to numerous health benefits, the findings are surprising, even to experts – but they should be taken with a grain of salt: It's a small animal study that offers some context to common dietary approaches that should be explored further.

"The study is intriguing because it challenges the oversimplified idea that removing sugar is automatically beneficial," Nneoma Oparaji, a US-based physician, told Medical News Today.

However, "nutrition is more complex and nuanced than removing a single ingredient," she added.

These results still need to be replicated in humans, which may shed more light on how they might relate to treatments for conditions such as diabetes – where blood sugar control is so important.

For now, the study highlights the need to further investigate the effects of cutting out sugar entirely.

We've previously seen with certain restrictive diets that turning the dial too far towards a perceived 'ultra-healthy' level can be detrimental.

While a 2024 Swedish study cautiously concluded that an occasional sweet treat could be good for cardiovascular health, the source (food or drink) and type of the sugar mattered.

Related: Blood Sugar Spikes Linked With 69% Higher Risk of Alzheimer's

Those gut bugs, it seems, can be quite influential.

"These findings suggest that sucrose elimination from a low-fat diet disrupts gut microbiota, impairs metabolic homeostasis, and promotes gut and liver inflammation, revealing an unrecognized dietary trigger of metabolic dysfunction," the researchers conclude.

The research was presented at ENDO 2026, the annual meeting of the Endocrine Society, and has been accepted in Frontiers in Immunology: Nutritional Immunology.