Water-Only Fasting Diets May Increase Inflammation, Study Finds

Water-only fasting diets and the study findings

Suggestions that you try water-only fasting diets may be appearing more often in your social media feeds. However, researchers are advising people to obtain medical guidance before beginning such diets because of their possible harmful effects.

A new study by an international research team examined the impact of water-only fasting diets in 20 people across 10 days. Participants consumed nothing apart from water, with no other beverages allowed. They lost an average of 7.7 percent of their body weight, but reported side effects such as headaches, insomnia and low blood pressure.

On balance, fasting appeared to heighten inflammation and place the body under greater stress. This could subsequently 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."

Inflammation markers during prolonged fasting

The researchers primarily assessed fasting’s effects by measuring protein levels in the body. Several proteins associated with inflammation, including C-reactive protein (CRP) and interleukin 8 (IL-8), were found in substantially higher amounts in participants’ blood plasma.

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

Why medical advice is important

The evidence remains fairly inconclusive. These are early results from a small group of individuals, all medically classified as overweight. Outcomes could differ in larger samples or among people with other body types.

Going without food for a prolonged period also appears to have potentially serious disadvantages. Medical advice should therefore always be obtained before starting 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 notes earlier studies that have identified possible benefits of intermittent fasting, including slower cellular ageing, lower inflammation-the reverse of the effect observed in this study-and a reduced risk of disease. The overall picture is therefore complex.

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 it too has disadvantages that need consideration.

What does appear clear is that fasting does not offer a one-size-fits-all approach. Any effort to lose weight by cutting off the body’s food and energy supply must be managed carefully.

"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 was published in Molecular Metabolism.