After intermittent fasting, which involves alternating periods of eating and fasting at given times, water fasting has become the latest craze on social media for its supposed health benefits.
This involves consuming only water and other liquids – coffee, tea, infusions, broths – for a day or more. According to its followers, this fast can help you lose weight and revitalise your digestive system.
There are many ways to practise water fasting, but experts agree that the ideal duration is five days, once a year. For those new to the concept, an initial period of 24-48 hours is recommended. But is it really an effective solution for weight loss?
According to a 2023 study from the University of Illinois Chicago, published in the journal Nutrition Reviews, water fasting may not be effective for long-term weight loss. This review of eight studies on water fasting reported that participants experienced significant weight loss, but just in the short term.
Those who fasted for five days lost 4-6% of their initial weight, while those fasting for 7-10 days lost 2-10%, and those fasting for 15-20 days lost 7-10% of their original weight.
In one of the studies reviewed, which tracked participants’ weight after the fast ended, people were found to have gained back all they had lost within three months.
“My overall conclusion is that you could try it, but it just seems like a lot of work, and all those metabolic benefits disappear,” lead researcher Krista Varady said.
Water fasting can have side effects, including mood swings, migraines and vomiting. It can exhaust you physically and mentally, preventing you from engaging in strenuous physical activity.
Varady also noted that “participants in these prolonged fasts lost about two-thirds of their weight in lean mass and one-third in fat mass. This is the opposite of what happens most of the time during weight loss, where more fat is lost than muscle”.
Water fasting is not recommended for certain categories of people, including children and adolescents, people with medical conditions such as diabetes, pregnant and breastfeeding women, and adults over 75.
“When done long-term, water fasting can be dangerous and even fatal without medical supervision because of nutrient and electrolyte imbalances,” Kaytee Hadley, a US-based functional medicine dietitian, told Forbes.
It’s crucial to consult a doctor before attempting prolonged fasting, as going 24 hours or more without food can be dangerous. Finally, it’s worth remembering that water fasting is not a miracle solution for weight loss or detoxification.