A new study reveals that water-only fasting may come with serious side effects that include inflammation and/or muscle loss.
It sounds simple. Stop eating, drink only water and the weight will melt away.
For a growing number of people scrolling through social media or wellness blogs, water-only fasting has become the latest 'quick fix' for losing weight and boosting health.
But a recent study by the University of Sydney is challenging the hype and raising important questions about the real risks behind this extreme wellness trend.
The research, published in Molecular Metabolism, was a collaborative effort by scientists from Australia, Italy and the US. It followed 20 healthy adults (11 women and nine men) through a 10-day water-only fast and a five-day refeeding period. Participants were closely monitored before, during, and after the trial.
While the weight loss results were striking -- an average 7.7 per cent reduction in body weight and a six per cent drop in waist circumference -- the researchers discovered something far more concerning in the participants' bloodwork.
Participants also reported short-term side effects like headaches, low blood pressure and insomnia -- common complaints during extended fasting.
Researchers also noticed alarming side effects.
'Our hypothesis was that prolonged water-fasting would reduce inflammation in the body,' said Professor Luigi Fontana, the lead researcher from the University of Sydney's Charles Perkins Centre. 'However, we found the opposite was true -- that prolonged fasting put stress on the body and increased the number of pro-inflammatory proteins in the blood, potentially increasing the risk of health issues for people with existing heart and vascular conditions.'
Blood tests showed rising levels of inflammation, including proteins like C-reactive protein (CRP) and interleukin-8 (IL-8), markers linked to systemic inflammation -- a known contributor to heart disease, autoimmune disorders and other chronic illnesses.
Muscle and bone-supporting proteins also dropped -- meaning the body wasn't just burning fat. It was breaking down lean tissue.
While the body was shedding pounds, it may also have been sacrificing its structural health -- a trade-off that raises serious concerns for long-term well-being.
The study also noted a decrease in amyloid beta proteins, which are associated with the development of Alzheimer's disease. This suggests that water-only fasting might have some neuroprotective effects.
However, researchers emphasised that while certain metabolic markers may improve during a fast, the full picture is far more complex -- and in many cases, potentially harmful.
With wellness influencers glamorising multi-day water fasts as detoxifying, anti-aging or spiritually enlightening, many are tempted to dive in without fully understanding the risks.
That's why the team at the University of Sydney is issuing a clear warning, especially for those with existing health concerns.
People with health conditions, particularly those related to the heart or circulation, should definitely talk to their doctor before attempting any kind of fasting diet, experts advise.
So is water-only fasting worth it?
The answer, according to the experts, is complicated.
While short-term weight loss is nearly guaranteed, the physiological stress, potential muscle and bone degradation and immune system agitation make it a high-risk method -- particularly without medical supervision.
The study's authors also pointed out that current data is limited and drawn from small sample sizes, making it difficult to predict long-term outcomes or generalise findings.
Water fasting can lead to fast weight loss. But it also comes with real risks: inflammation, nutrient deficiencies, muscle loss and more.
The latest science suggests that the risks could outweigh the rewards, especially for those dealing with cardiovascular issues or other chronic conditions.
Until larger, longer-term studies provide clearer answers, experts urge caution and consultation with healthcare professionals before attempting extended fasts.
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