The major advantage of juicing is that it can help increase intake of fruits and vegetables that you otherwise may not have been eating. Preparing your own juice is good for you in that it will give you a drink that is tastier and more nutritious than prepared, bottled juices. One reason for the taste difference is that commercial juice is treated with heat to kill germs, which makes it safe for storage but alters taste and lowers nutritional value. Home squeezed citrus juice will retain more of the fruits’ inherent health benefits, which can include lowering levels of inflammation and decreasing risks of heart disease. And, since juice prepared at home contains pulp, you also get some healthful dietary fiber.
As for the drawbacks: a big one is the fact that home-squeezed juices tend to break down quickly if they remain exposed to air - pathogens can grow in them between extraction and consumption, just as they can in commercial juices. For that reason, it's important to drink juice soon after you prepare it rather than making several days' supply at once and storing it.
If you modify your diet to consist mostly of fruit juices, you’ll be getting much more sugar and less fiber than you need. There’s a big difference between fruit and fruit juice. Fruit juice is a concentrated sugar source that can promote insulin resistance and obesity when consumed in quantity. Vegetable based juices are much less of a problem in this regard.
But there’s no doubt that juicing is becoming more and more popular. The Wall Street Journal has reported that annual sales of juice extractors for home use hit $215 million in November 2012 – up 71% over the previous year – at prices ranging from $150 to nearly $700.
Enthusiasts (and some manufacturers) make all sorts of health claims for juicing – that it can reduce the risk of cancer, boost your immune system, help remove toxins from your body, aid digestion, help you lose weight, improve your skin and increase your energy, but I’ve seen no scientific evidence demonstrating that juices are as good as the whole fruits or vegetables they came from.
Andrew Weil, M.D.