Water has long been known to be ideal for quenching both thirst and hunger pangs but some people have been taking it a step further. Some dieters have tried giving up all other food and drink for days at a time and living on just the calorie-free liquid.
Many have claimed success on the scales but there have also been other benefits spotted during studies. These have included lower blood pressure and improved cholesterol.
But how much weight can you lose, does it stay off and just how long-lived are the other benefits. A new study has examined just how successful the practice is - and if it is worth doing.
According to the research by the University of Illinois Chicago water fasts might help you lose weight, but it’s unclear how long you’ll keep it off. And the other metabolic benefits of water fasts, such as lower blood pressure and improved cholesterol, seem to disappear soon after the fast ends, the researchers found.
However, there do not appear to be any serious adverse effects for those who do a water fast or a similar kind of fast where people consume a very small number of calories a day, said Krista Varady, professor of kinesiology and nutrition, who led the research, which is published in Nutrition Reviews. “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.
She stressed, however, that no one should undertake one of these fasts for more than five days without medical supervision. Her paper is a review of eight studies on water fasting or Buchinger fasting, a medically supervised fast that is popular in Europe where people consume only a tiny amount of juice and soup a day.
Varady’s team looked at the results from each of those papers to see what story they cumulatively tell about the fasts’ impact on weight loss, as well as a number of other metabolic factors. This is what they found.
Will you lose weight?
Fasting did seem to spur noticeable short-term weight loss, the researchers found. People who fasted for five days lost about 4% to 6% of their weight; those who fasted for seven to 10 days lost about 2% to 10%, and those who fasted for 15 to 20 days lost 7% to 10%.
However Varady noted that the 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.
It makes sense that these extreme fasts would have this result, she said, because “your body needs a constant intake of protein. If it doesn’t have that, then it draws from muscles.”
Will it stay off?
Only a few of the studies in the review tracked whether participants gained back the weight they had lost once the fast ended. In one of those, people gained back all they had lost in a five-day water fast within three months.
In two other studies, only a small amount of the lost weight returned, but those studies encouraged participants to restrict their calorie intake after the fasts ended.
What about other health benefits?
According to the study it was clear that the metabolic benefits of the fasts disappeared soon after the fasts ended. Improvements to blood pressure, cholesterol and blood sugar levels were short-lived, returning to baseline levels quickly after participants started eating again.
Is it safe?
Some of the studies included participants with Type 1 and Type 2 diabetes, who suffered no ill effects from the fasting, though they were monitored closely and had their insulin doses adjusted while fasting.
The most common side effects of these prolonged fasts were similar to those from intermittent fasting, Varady said, such as headaches, insomnia and hunger. There were no serious negative effects in the studies, such as metabolic acidosis or death.
A better alternative
Varady said she would encourage someone hoping to lose weight to try intermittent fasting instead of a water fast, “because there’s a lot more data to show it can help with weight management,” she said.
