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Are water fasts worth it? Probably not, suggests a new study

Water fasts, which involve ingesting only water for several days at a time, were traditionally observed for their potential spiritual or therapeutic benefits. Recently, water fasts have been gaining traction in the world of weight loss and wellness. 

However, a new study from the University of Illinois Chicago suggests that the rapid weight loss from these extreme fasts might be as quickly regained. Also, additional metabolic advantages such as lowered blood pressure and improved cholesterol levels, may prove fleeting.

The research was led by Krista Varady. She is a professor of Kinesiology and Nutrition and an expert on intermittent fasting.

The study was recently published in the journal Nutrition Reviews. It did not unearth any serious negative repercussions for those who undergo water fasts. Nor did it identify major problems for a similar fasting method where caloric intake is minimally maintained.

“My overall conclusion is that I guess you could try it, but it just seems like a lot of work, and all those metabolic benefits disappear,” said Professor Varady.

The study does not outright discourage water fasts. However, Varady emphasizes that any such fast extending beyond five days should be undertaken only with medical supervision.

How the research team studied water fasts

The decision to probe into water fasts emerged after a surge of journalistic interest in the practice. Professor Varady set out to scrutinize existing research with a literature review before making an informed comment.

Varady analyzed eight studies on water fasting and Buchinger fasting. Buchinger is a popular European fasting variant that involves consumption of minimal amounts of juice and soup daily.

Each of these studies was closely studied to gauge the collective narrative they presented on the impact of these fasts on weight loss and other metabolic factors.

Rapid weight loss and water fasts

Clear evidence of short-term weight loss surfaced from these fasting practices. Five-day fasts typically resulted in a 4% to 6% loss of body weight.

Water fasts lasting between seven to 10 days led to a weight loss of about 2% to 10%. For water fasts that extended between 15 to 20 days, participants lost between 7% and 10% of their body weight.

However, few studies monitored the participants’ weight after the completion of the fast. In one such study, participants regained all their lost weight within three months.

While a small amount of the lost weight was regained in two other studies, these studies advocated caloric restriction following the fasting period.

Metabolic effects of water fasts

A marked transient effect was observed in the metabolic benefits associated with fasting. This included improvements in blood pressure, cholesterol and blood sugar levels swiftly returning to baseline after the fasting period.

Interestingly, some studies included participants with Type 1 and Type 2 diabetes. While closely monitored and with adjusted insulin doses, these participants reported no ill effects from the fasting.

Common side effects of prolonged fasting mirrored those of intermittent fasting, with headaches, insomnia, and hunger being the primary complaints. However, Varady noted that no serious negative effects, such as metabolic acidosis or death, were reported in the reviewed studies.

A peculiar finding was the disproportionate loss of lean mass compared to fat mass in these prolonged fasting regimens. Typically, weight loss is characterized by more fat loss than muscle loss. However, the extreme nature of these fasts reversed this trend. Varady explained: “your body needs a constant intake of protein. If it doesn’t have that, then it draws from muscles.”

Noting the scarcity of supportive data for water fasting, Varady, whose research into intermittent fasting has revealed no impact on fertility, would recommend someone seeking weight loss to try intermittent fasting. She pointed out that there is “a lot more data to show it can help with weight management.”

History of water fasting

Fasting, in its various forms, has been practiced by cultures across the globe for millennia. Water fasting, specifically, involves consuming nothing but water for a period of time, and its history is rooted in both spiritual and physical healing practices.

Religious practices

Historically, water fasts were often undertaken for religious or spiritual purposes. Many major religions, including Christianity, Islam, Judaism, and Buddhism, have traditions of fasting, which sometimes include periods of consuming only water. These fasts were used as a form of purification, repentance, or spiritual enlightenment.

Physical health

In the realm of physical health, water fasts have been used in various traditional medicine practices. Ancient Greek philosophers and physicians, including Hippocrates, Plato, and Galen, often recommended fasting to improve health. Hippocrates, known as the Father of Medicine, is believed to have said, “Instead of using medicine, better fast today.”

Natural hygiene and self-healing 

Fast forwarding to more modern times, the 19th and early 20th centuries saw a surge in the popularity of “natural hygiene,” a health movement that often advocated fasting as a means of allowing the body to heal itself. For example, Dr. Herbert Shelton, an influential figure in the natural hygiene movement, supervised the fasts of more than 40,000 patients during his career.

In the late 20th and early 21st centuries, interest in water fasting has resurged, often as a method for quick weight loss. Despite its current popularity, it is still considered an extreme method and should only be undertaken with appropriate medical supervision.

It’s important to note that while water fasting may have a long history, this does not automatically equate to safety or effectiveness, especially for long-term health. As shown by the recent study from the University of Illinois Chicago, the weight loss benefits of water fasting can be short-lived and could potentially result in rapid weight regain, while any additional metabolic advantages appear to be fleeting.


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