When I refer to "juicing" I'm really referring to juice fasting or cleansing, that is limiting the diet to only the juice extracted from fresh fruit and vegetables for a certain amount of time. I don't remember when juicing became so popular, but it may have happened after the 2010 film Fat, Sick & Nearly Dead hailed 60-day juice fasts as the pathway to health (1). Which, unfortunately, I have not watched.
Cold-pressed juices seem to be all the rage. So what is the cold-pressing process?
Fruits and vegetables are fed into a tube that leads to an auger (which grinds & chews the produce to a paste) this paste is then forced through the remainder of the shaft, allegedly extracting more juice per piece of produce than the traditional centrifugal juicer. Proponents of this movement claim the slower process, lack of oxygen, and lack of heat (which is generated by the motor & spinning blades in a centrifugal unit) leaves more nutrients in the juice. At this time, there is no clinical research to show increased nutrient composition of cold pressed juices vs traditionally juiced juices (2). More than the concern about bioavailablilty of the nutrients, if you're drinking these juices sans pulp, you're missing out on the vital nutrients in the skins (particularly fiber) that you'd find in whole fruits/vegetables.
Unfortunately, despite the popularity of this diet, there is very limited clinical information on juice cleanses, and the information available seems to be from studies with too-small sample sizes, and are not long enough to show any long term consequences of this diet (whether positive or negative). Along with the limited clinical studies, there is also limited information to suggest the efficacy of the process of cold pressing fruit/vegetables to enhance or maintain bioavailability of nutrients (1). Although, for someone who dislikes fruits or vegetables, and therefore isn't getting the recommended 5-a-day fruits/vegetables, juicing is certainly better than not consuming adequate amounts of fruits and vegetables.
But isn't it always better to get more fruits and vegetables in your diet? Are there dangers to this diet?
Up to now, there haven't been any reports of juicing-induced damage, until the reporting of a case of oxalate nepropathy (oxalate induced acute kidney failure) due to 6 weeks juicing fast as reported in the American Journal of Medicine.
Although this case study focuses on a patient with the pre-existing condition of stage 3 chronic kidney disease (almost to the point of needing dialysis to filter his blood), the risk for possible kidney damage is increased by consuming high amounts of oxalate containing fruits and vegetables (such as beets, collard greens, kiwi, parsley, spinach, and soy products). If you are eating from all 5 food groups, consuming adequate dairy will decrease risk of accumulating oxalates in the blood (as calcium binds them and prevents their absorption!) Therefore, high oxalate diet without adequate calcium can increase risk of kidney disorders and other pathophysiological issues (3).
Overall, increasing your fruit and vegetable consumption is always great! I would always recommend whole fruits over juice, but if eating whole fruits/vegetables isn't logical for you, juicing is better than nothing! When it comes to the "juice fasting" concept, in my clinical experience it would likely not cause any significant damage if followed for a few days a couple times per year. You just may not have the energy or brain power to work or exercise, and a juice diet would likely be deficient in required calories for body function, protein for muscle building, and vitamin B12, which keeps your blood cells healthy. I personally drink juice (no matter it being from fruits or vegetables) as a treat or to occasionally be part of my 5-a-day (because I really do like fruits and vegetables) instead of relying on it to lose weight or to "reset" my metabolism or body. All foods/drinks can fit into a healthy diet, its just about moderation....
1. Jessica Cording. Juice: From Weight Loss to Detox, this Trend is Taking Off. Food & Nutrition Magazine. 2012. http://www.foodandnutrition.org/Spring-2012/Juice-From-Weight-Loss-To-Detox-this-Trend-is-Taking-Off/
2. Food and Nutrition. What is cold-pressed juice? Food and Nutrition Magazine. 2013. http://www.foodandnutrition.org/July-August-2013/What-is-cold-pressed-juice/
3. Yeong-Hau Lein. Juicing is Not All Juicy. Dept of Medicine, College of Medicine, University of Arizona, Tuscon Arizona Kidney Disease and Hypertension Center, Tuscon. American Journal of Medicine. 126(9) 755-56. 2013. http://www.amjmed.com/article/S0002-9343%2813%2900390-2/fulltext.