The answer is a resounding no! Juice fasts and cleanses -- which involve consuming 1,200 calories or less in just liquids each day -- go up and down in popularity, depending on how many celebrities are on them. But they are always an unhealthy way to lose weight -- and often an unpleasant one as well.
Why? Well, first of all, your body doesn't know that you just want to drop a few pounds. Instead, it thinks you're starving it. The result: Just like any crash diet, your metabolism slows and your body holds on to fat in order to preserve itself. Any weight you lose will be mostly water, which you'll quickly regain as soon as you start eating real food again. In addition, your body is perfectly able to cleanse itself without a juice fast. It doesn't need one (or the colonics that are often recommended with them) to detox.
And if you're planning to fast, you'd better stay at home and away from friends, family, coworkers ... basically everyone. An all-liquid diet is far from satisfying. You can expect to be hungry all the time -- and really, really cranky. Some of my clients who tried fasting before they came to me describe feeling so ravenous that they couldn't think of anything but food. As you can guess, that inevitably leads to bingeing, and all you have to show for your suffering is several days of torture.
Finally, real health risks are associated with fasting. With all the fiber removed in the juicing process, your body gets a big shot of sugar from the fruit juice and even the vegetable juice. This can cause dangerous blood sugar spikes and crashes in diabetics (including many who are undiagnosed) or those who are insulin-resistant. And if you fast often enough, you could permanently lower your metabolism.
My advice: Stick to a weight loss plan where you can eat real food and enough of it so you aren't hungry. I recommend that your total daily calories never dip below 10 times your goal weight (e.g., 1,500 calories if your goal weight is 150 pounds). That's the way to lose weight without suffering -- and actually keep it off.