Juicing is the process of extracting liquid from fresh fruits and vegetables while separating out most of the solid fiber and pulp. The result is a concentrated, nutrient-dense drink that delivers vitamins, minerals, and plant compounds in a form your body can absorb quickly. It’s distinct from blending (which retains all the fiber) and from store-bought pasteurized juice (which has been heat-treated for shelf stability). Whether people juice for convenience, taste, or health goals, understanding what actually happens to the produce during juicing helps you get the most out of it.
How Juicing Works
A juicer mechanically crushes, grinds, or spins fruits and vegetables to force liquid out of the plant cells, then passes that liquid through a strainer or filter. What comes out is water, natural sugars, and a concentrated mix of micronutrients. What stays behind in the pulp is most of the insoluble fiber, the rough, structural material that gives produce its texture.
This fiber removal is the key distinction between juicing and blending. When you blend a smoothie, the entire fruit or vegetable goes in and stays in. Research comparing the two methods found that blended fruit drinks contain higher levels of polyphenols and flavonoids (protective plant compounds tied to the fiber and pulp), while juiced versions retained more vitamin C. Each method has trade-offs, and the “better” choice depends on what you’re after.
Types of Juicers
The two main categories of home juicers work very differently, and the difference matters for juice quality.
- Centrifugal juicers use a rapidly spinning blade to shred produce, then fling the liquid outward through a mesh filter using centrifugal force. They’re fast, usually more affordable, and handle most fruits and hard vegetables well. The downside is that the high-speed blade generates some heat and exposes the juice to more air, which can accelerate oxidation and slightly reduce heat-sensitive nutrients.
- Masticating juicers (also called cold press or slow juicers) use a slowly rotating auger to crush and squeeze produce. Because there’s minimal heat buildup, they tend to preserve more vitamins, enzymes, and color. They also extract juice more thoroughly from leafy greens, which centrifugal models struggle with. The trade-off is speed and price: they take longer and typically cost more.
For casual juicers making a glass or two a few times a week, either type works fine. If you’re juicing daily or prioritizing leafy greens, a masticating juicer is the more practical choice.
Nutrient Absorption From Juice
One of the main selling points of juicing is that nutrients in liquid form may be easier for your body to absorb, and there’s real evidence behind this. A randomized crossover study comparing vitamin C absorption from whole raw fruits and vegetables versus their juice found that the juice group had the highest plasma vitamin C levels, peaking about two hours after consumption. The total vitamin C absorbed over 12 hours was roughly double in the juice group compared to one of the whole-food groups. In short, removing the fiber lets your gut access certain vitamins faster and more completely.
That said, this doesn’t mean juice is nutritionally superior to whole produce. The fiber you lose during juicing feeds beneficial gut bacteria, slows digestion, and helps regulate blood sugar. Juice delivers micronutrients efficiently, but it’s not a complete replacement for eating whole fruits and vegetables.
Sugar and Blood Sugar Effects
A common concern about juicing is that it concentrates fruit sugar into a form that spikes blood sugar. This is partly true, but the picture is more nuanced than it first appears. One study measuring glycemic index found that blended fruit mixtures (which retain all the fiber and pulp) actually produced a lower blood sugar response than eating the same fruit whole, with GI values dropping from roughly 45 to 25 in participants with obesity. The fiber and other plant compounds in the liquid slowed glucose absorption.
Pure juice with the fiber removed is a different story. Fruit-heavy juices, especially those made from high-sugar fruits like grapes, mangoes, or pineapples, can deliver a significant sugar load with little to slow its absorption. A practical rule: the more vegetables and the fewer sweet fruits in your juice, the lower the sugar impact. Greens like kale, cucumber, and celery contribute minimal sugar, while a small amount of apple or lemon keeps the flavor palatable.
How Quickly Juice Loses Nutrients
Fresh juice starts losing vitamin C the moment it’s made, but the rate depends heavily on how you store it. Research tracking vitamin C stability found that juice kept refrigerated at about 40°F in a glass container lost only 0.4% to 2.2% of its vitamin C in the first 24 hours. That’s negligible. By 48 hours, losses climbed to between 2% and 14%, and by three days, up to 18%.
Leave that same juice at room temperature, and degradation accelerates dramatically: up to 22% loss in just 24 hours, and as much as 37% gone by day three. The takeaway is straightforward. Drink your juice within a day or two, keep it cold, and store it in a sealed glass container with as little airspace as possible. The less air and heat, the more nutrients survive.
Oxalate Risk From Green Juices
Green juices built around spinach, chard, or beet greens carry a specific risk worth knowing about: oxalates. These naturally occurring compounds bind to calcium and, in high enough concentrations, can contribute to kidney stone formation in susceptible people. Juicing actually makes this problem worse, not better. When researchers compared green juices with and without the pulp, they found that removing the pulp (as juicing does) resulted in significantly higher oxalate levels in the remaining liquid.
This doesn’t mean you need to avoid green juice entirely. Cutting the spinach content in half dramatically reduced oxalate levels in the same study. Rotating your greens is the simplest fix: use kale, romaine, or cucumber as your base instead of relying on spinach every time. If you have a history of kidney stones, this is especially worth paying attention to.
Food Safety at Home
Raw, unpasteurized juice can harbor bacteria like E. coli and Salmonella. The FDA has documented outbreaks of foodborne illness traced to untreated juice and cider. Commercially sold unpasteurized juice is required to carry a warning label, but juice sold by the glass at juice bars, farmers’ markets, and restaurants has no such requirement.
When juicing at home, the FDA recommends washing your hands thoroughly before and after handling produce, scrubbing firm-skinned items like apples and cucumbers with a clean brush, and cutting away any bruised or damaged areas before juicing. Wash all produce under running water even if you plan to peel it, since bacteria on the surface can transfer inward when you cut. Skip soap or commercial produce washes, which aren’t recommended. Dry everything with a clean towel before juicing to further reduce surface bacteria.
Juicing and Overall Diet Quality
Only about 12% of U.S. adults meet the recommended daily fruit intake, and just 9% eat enough vegetables. Juicing can make it easier to consume a wider variety of produce, especially vegetables you might not enjoy eating whole. A large analysis of national dietary data found that adults who consumed 100% fruit juice had better overall diet quality scores, though their vegetable intake wasn’t significantly different from non-juice drinkers.
This highlights an important point: juicing works best as a supplement to a diet that already includes whole fruits and vegetables, not as a substitute for them. The fiber, chewing satisfaction, and slower digestion you get from whole produce serve functions that juice simply can’t replicate. But if the alternative is skipping fruits and vegetables altogether, a daily juice puts you meaningfully closer to your nutrition goals.