Water-Only Fasting Diets May Increase Inflammation, Study Warns

Recommendations to try water-only fasting diets may be increasingly common on social media, but researchers are urging people to get medical advice before embarking on them because of their possible harmful effects.

Water-only fasting diets and the study findings

An international group of researchers has released a study examining the impact of water-only fasting diets in 20 people over 10 days. This meant consuming only water, with no food or other beverages. Participants lost an average of 7.7 percent of their body weight, but they also reported side effects such as headaches, insomnia and low blood pressure.

On balance, fasting appeared to raise inflammation and place the body under greater stress. This could in turn result in a range of health complications, particularly in people who already have heart or vascular conditions.

"Our hypothesis was that prolonged water-fasting would reduce inflammation in the body," says physician scientist Luigi Fontana, from the University of Sydney.

"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."

The researchers primarily assessed fasting's effects on the body by measuring protein levels. Several proteins associated with inflammation, including C-reactive protein (CRP) and interleukin 8 (IL-8), were far more plentiful in participants' blood plasma.

Inflammation, protein changes and health concerns

The study also identified other changes. Proteins connected with the breakdown of muscle and bone declined, as did amyloid beta proteins, which are strongly linked to the development of Alzheimer's disease.

The findings remain comparatively uncertain, however. They represent early results from a small group of people, all medically classified as overweight. Outcomes could differ in larger groups or among people with other body types.

There also appear to be substantial disadvantages to depriving the body of food for a prolonged period. Medical guidance should therefore always be obtained before beginning a diet of this kind.

"While the acute inflammatory response during prolonged fasting may serve as a transient adaptive mechanism, it raises concerns regarding potential cardiometabolic effects that could persist after refeeding," write the researchers in their published paper.

"Further investigation is warranted to elucidate the long-term molecular and clinical implications of prolonged fasting across diverse populations."

The team highlights earlier research indicating that intermittent fasting could help slow cellular ageing, reduce inflammation - unlike the effect observed in this study - and lower disease risk, making the overall picture a complicated one.

Intermittent fasting versus prolonged fasting

In recent years, intermittent fasting has received more attention than prolonged fasting. It appears that intermittent fasting needs to be paired with calorie control to deliver weight-loss benefits, and there are still disadvantages to weigh up.

What does appear evident is that fasting is not a one-size-fits-all approach. Any effort to lose weight by cutting off the body's food and energy supply requires careful management.

"People are looking for effective ways to manage their weight and while the effects of water-only fasting can be dramatic, more work needs to be done to understand the impact of these diets on the body over a longer period of time," says Fontana.

The research has been published in Molecular Metabolism.