This may seem like a strange thing to argue about, because the popular consensus still seems to be that juice is healthy. Jamba Juice markets itself as "the category-defining leader in healthy blended beverages, juices, and good-for-you snacks." They even use Jamba as an adjective to mean the opposite of high fructose corn syrup and trans-fats (adding those things to juice ""just wouldn’t be Jamba"), which again, constructs the brand as healthy vs. the demon poisons that make people fat. Even if it’s foolish to go looking for truths in advertising, I don’t think Jamba Juice’s branding generally occurs to people as a massive irony or lie. Advocates of banning or restricting soda vending machines in schools often claim that the soda should be replaced with 100% fruit juice with no added sugars, and for many people, a glass of orange juice still represents "part of a nutritious breakfast" strongly with desirable nutrients like Vitamin C.
The Case Against Juice
But a number of health trends have begun cast suspicion on juice, especially the (impartial and incomplete) shift from primarily low-fat to primarily low-calorie and low-carb dieting in mainstream weight-loss culture, and the growing concern about the role sugars (especially fructose) play in personal and national obesity.
On the low-calorie front, people who believe that losing weight or maintaining a healthy weight is all about the basic algebra of calories-in vs. calories-out often end up axing all caloric beverages from their diets because they have a bad satiety-to-calorie ratio—I mean, obviously, right? Fruit juice is just fruit with some or all of the filling fiber removed. If the goal is maximum satiety on minimum calories, you’re better off eating whole fruit and drinking water or artificially sweetened beverages.
On the low-carb front, people who believe that what’s important is not how many calories you eat but what kind are also going to see juice (and sometimes most fruits and vegetables as well) as "unhealthy." It does seem to be true that diets high in carbohydrates drive up insulin levels, slowing metabolism and encouraging the body to store fat. And the overwhelming majority of the calories in most fruit juices are in the form of carbohydrates. Some green vegetable juices have protein content approaching 50% of the carbohydrate content, but that just makes it 75% bad rather than 100% bad, at least as true carbophobes are concerned.
And finally, there are some non-carbophobes who might avoid juice because they’re wary of sugar qua sugar, rather than sugar qua carbohydrate. The carbohydrates in fruit juice primarily take the form of fructose—wikipedia has a handy chart of the kinds of sugars in common plant foods. It doesn’t seem like there’s a true consensus yet about whether or not fructose is especially bad—despite recent studies linking fructose to obesity, even within the medical community, some people still advocate fructose as a "low glycemic" sugar that’s better for diabetics. It basically all comes down to whether you think the fact that fructose is digested in the liver and doesn’t trigger insulin production is a good thing or a bad thing. To link it to other sugar purveyors: pro-agave nectar people should also think that fruit juice is healthy and people who think hfcs is bad because they think it’s "high fructose" compared to other sugars are, well, a) wrong, but b) should also be advocating hfcs-sweetened sodas over fruit juices, which are even richer in sugar.
Personally, I think the evidence that fructose in large amounts causes equivalent blood sugar spikes to other sugar, increased "bad" cholesterol and triglycerides and signs of insulin resistance compared to glucose, and can cause non-alcoholic fatty liver disease consumed in vast quantities suggests that it is certainly no better and possibly much worse for human health than glucose or sucrose. But "worse for human health" is relative, not absolute, and depends a lot on amount, kind, and context.
What is health?
I’m generally convinced by the argument made by people like Gary Taubes that a diet composed of almost-exclusively proteins and fats might better represent the pre-agricultural, hunter-gatherer diet (as would cyclical feast and famine) and prevent carbohydrate-induced insulin resistance and fat storage. Jared Diamond makes some of the same points in Guns, Germs, and Steel. But the benefits of agriculture ultimately outweighed the costs—both for the species as a whole and measured by individual health metrics. In the immediate aftermath of the transition to agriculture, lifespans and average height decreased, but after a few thousand years, people depending on rice, corn, and wheat began to get healthier again.
Does that mean carbohydrates are a healthier basis for a diet than proteins and fats? No. But it does mean that people can (and do) live very long lives uninterrupted by diet-based disease during which they are strong and energetic enough to physically do anything they want to do while eating a diet consisting substantially of carbohydrates. And I think that’s not a bad working definition of "healthy."
It seems to me that the debate comes down to a difference between ideas about nutritional "health" based on what might be theoretically optimal (for a very limited set of criteria), ideas about health based on potential pathology, and ideas about health based on actual health outcomes.
Fear of juice is based on the first two—the idea that either people should eat as few carbohydrates as possible in pursuit of some sort of optimal diet, or that the fructose in juice will cause fatness (an aesthetic problem, not a medical problem) or disease and eventually death. Based on actual health outcomes, I think it would be almost impossible to make a case for the claim that drinking fruit juice—occasionally or regularly—is categorically unhealthy or the direct cause of disease or death.
In fact, things like fruit juice and hamburgers and Doritos, which can each be constructed as "unhealthy" are hard to entirely rule out of a "healthy diet." Even proponents of a soda tax generally agree that the only reason soda is a reasonable target is because it has no identified nutrients (what would happen if they fortified them, I wonder?).
The nutrient-density of juice is the primary reason for the long tradition of juice being regarded as a health food. If your concern is about essential vitamins and minerals (like many older models of nutrition, which people like Marion Nestle stand by) or consuming carbohydrates for fuel, which many physically active people still do, it’s hard to argue with the healthfulness of juice. I agree with Michael Pollan’s claim that popular beliefs about health often fall prey to "nutritionism," or the attempt to reduce food and nutrition to scientifically-identified nutrients and vitamins. At the same time, I don’t think you have to be brainwashed by the continued prevalence of nutritionism to believe there’s good evidence that many of the nutrients that scientists have identified are actually valuable or promote health and well-being (even if they’re not the only valuable aspects of food).
All juices are not created equal
The person who requested this entry was concerned specifically about fresh juices being portrayed as unhealthy, because they seem to have been smeared by concerns about packaged juices being just other source of dietary sugar.
While not all fruits lend themselves as readily to the production of refined sugars as sugar beets, some like apples, pears, and grapes can be turned into a nutrient-poor sweetener without most of the fruits’ color, flavor, or minerals and many fruit juices marketed as 100% natural fruit juices, like Juicy Juice, are sweetened with fruit juice that’s basically been turned into a sugar syrup. The nutritional distinction between those drinks and hfcs-sweetened soda is probably negligible regardless of whether your primary concern is calories, carbohydrates, sugar, or vitamins.
But the reason packaged juices often combined with fruit-based sugar is that many fruit juices aren’t actually that sweet on their own, or their sweetness is offset by the intensity of the flavor, as anyone who’s ever tried 100% cranberry or concord grape or cherry or blueberry juice knows. The fresh juices you can get at juice bars or make at home are calorie-dense, but they’re also extraordinarily nutrient dense and not likely to be consumed in quantity or alongside meals. They’re more often enjoyed on their own, like a snack, particularly after a workout—basically just like fruit. When you leave in some of the pulp, it becomes even less nutritionally distinct from fruit, and when you include vegetable juices or the juices of things like wheatgrass and ginger which are difficult or unpleasant to eat raw, you may be enjoying something that could, by some criteria, be healthier than a piece of fresh fruit.
Some juices even have pretty well-established medicinal uses. Cranberry juice, for example, can help prevent and cure urinary tract infections (that study notes the existence of "diet" cranberry juice, which I’d never heard of, but now that I have I wonder why there aren’t more "diet" juices sweetened with artificial sweeteners rather than pear or grape juice-sugar. Not that those would necessarily be "healthy" by everyone’s standards, especially given the links between saccharin and cancer and suspicions about the healthfulness of aspartame and sucralose…)
Ultimately, while I don’t think even the occasional hfcs-sweetened Capri Sun is incompatible with a "healthy" diet and life, I think it’s unreasonable to conflate fresh juice without added sweeteners with juices sweetened with refined juice-sugar. I guess people trying to eat an "optimal" diet a la Gary Taubes should avoid all juices, fresh or no, but I don’t envy them their carbohydrate-less life, nor am I convinced that the total deprivation of many foods that have aesthetic, gustatory, social and/or cultural value is necessarily "healthy" or "optimal" either. For the vast majority of people who think fruit and vegetables are part of a healthy diet, fruit juice and especially fresh fruit juice should also pass muster as a "healthy" choice especially when consumed in moderation, which I suspect fresh fruit juices usually are.