Fruit juice fasting has been popularized by products like the “Hollywood Diet,” which promises weight loss within hours. In general, products like these work in the short term, but are not effective at keeping the weight off in the long term.
When a person stops eating solid food, it causes them empty the contents of their digestive system without replacing them. This process will cause most people to lose 5 pounds within about day, and it often referred to as “cleansing.” Naturally, when a person starts eating solid food again, that weight (which is not body mass, but rather, digestive mass), comes back.
In addition, many people consume thousands of “empty calories” every day in the form of candy, sweets, sodas, and other sugary substances. When they embark upon a fruit juice fast, they give up these foods. The shock of all of those calories being empty causes the body’s metabolism to temporarily leap into high gear. This can cause another rapid, albeit small, weight loss. However, the metabolism will adjust after a brief period of time and compensate, using less energy to power the body as less calories from food come into it. This is why, after about a week, most fad diets leave people feeling listless and without energy. When the diet stops, the effect happens in reverse, with the weight coming back on quickly but the energy and metabolism taking a while to recover.
Many fruit juice fast products promise long term weight loss and an overall increases in bodily health. Both of these goals are unlikely to occur via juice fasting alone. Juice fasting is generally accepted as healthy, but only if done for a limited time, and not if done by those with diabetes. The vitamins in the juice are important, as many adults do not get their vitamins from their normal diets, but it is possible to consume both the juice and the solid food and get the benefits of the vitamins without the fast.
Most fad diets are unable to keep weight off because they trick the body into having a lower metabolism than it normally would. Since the juice fast cannot go on indefinitely, it is likely that the weight will come back. Furthermore, many people are understandably hungry after not eating solid food for so many days and binge – right at the moment when their metabolisms are slow and recovering, which is part of why the weight comes back so fast. This trend of yo-yo dieting is part of why most diets fail. They encourage a temporary change in habits, and the old body fat returns when the old habits return. Juice fasting is no exception. Unless one changes their long term eating and exercising habits at the conclusion of the diet, one should not expect long term weight loss as a result of a juice diet.
Fruit juice fasting for weight loss is very effective in the short term, due to the body’s natural responses to fasting and the effects of rapid calorie reduction. Due to the fact that one cannot get all of their essential nutrients from fruit, the fruit juice fast cannot last forever. When it ends, the weight is likely to come back unless one makes permanent changes to their lifestyle.
Cathy Wong, Juice Fast, About.com
AP, Dieting Most Always Fails, MSNBC.com