Prune juice is one of the highest-sugar fruit juices you can buy. A single 8-ounce cup contains about 42 grams of sugar, which is more than you’d get from the same amount of cola. That sugar is naturally occurring, not added, but your body still processes it as sugar.
How Much Sugar Is in a Cup
One cup of canned prune juice delivers roughly 42 grams of total sugar and about 2.5 grams of fiber. For context, the American Heart Association recommends no more than 25 grams of added sugar per day for women and 36 grams for men. While prune juice sugar is naturally occurring fructose and glucose rather than added sugar, a single glass still pushes past those thresholds in terms of sheer volume hitting your bloodstream.
Most major brands, including Sunsweet, contain no added sugar at all. The ingredient list is simply prune concentrate and water. That “no added sugar” label is accurate but can be misleading if you assume it means the juice is low in sugar. Prunes are extremely sugar-dense dried fruit, and juicing them concentrates that sweetness further.
How It Compares to Other Juices
Prune juice is notably more sugar-dense than most common fruit juices. One way to see this clearly: carbohydrate-counting guides used by diabetes educators list how much juice equals 15 grams of carbohydrate. For orange juice, apple juice, and grapefruit juice, that portion is half a cup. For grape juice, it’s a third of a cup. For prune juice, it’s also just a third of a cup, putting it in the same high-sugar tier as grape juice and well above citrus juices.
Spread across a full 8-ounce glass, prune juice lands around 42 grams of sugar compared to roughly 24 grams in orange juice and 28 grams in apple juice. Grape juice comes closest at about 36 grams per cup, but prune juice still tops it.
The Sorbitol Factor
Part of what makes prune juice unique is that not all of its sweetness comes from regular sugar. A cup contains about 10.5 grams of sorbitol, a sugar alcohol that your body absorbs much more slowly than glucose. Sorbitol draws water into the intestines, which is the main reason prune juice works so well as a natural laxative.
Sorbitol is lower on the glycemic index than regular sugar, so it doesn’t spike blood sugar as sharply. But it still contains calories, and in large amounts it can cause bloating, gas, and cramping. If you drink prune juice for constipation relief and find yourself with stomach discomfort, sorbitol is likely the reason.
What About the Fiber
Whole prunes are a genuinely good source of fiber, with about 3 grams in a serving of five or six prunes. Prune juice retains some of that fiber (around 2.5 to 3 grams per cup), which is unusual for fruit juice since most juicing processes strip fiber out entirely. That small amount of fiber does slow sugar absorption slightly compared to a completely fiber-free juice like apple or grape.
But 2.5 grams of fiber against 42 grams of sugar is not a meaningful offset. You’d need to eat whole prunes to get a better fiber-to-sugar ratio. Six whole prunes deliver comparable digestive benefits with less sugar and more fiber per serving.
Practical Serving Sizes
If you’re drinking prune juice for constipation, doctors typically recommend starting with 4 to 8 ounces per day. A 4-ounce serving (half a cup) cuts the sugar to about 21 grams, which is much more manageable and still delivers enough sorbitol to help with regularity.
If you’re drinking it because you enjoy the taste, treating it like a small glass rather than a full beverage makes a significant difference. Pouring 4 ounces instead of 8 is the single most effective way to get the benefits without the sugar load. You can also dilute it with water, which stretches the serving while reducing sugar concentration per sip.
Blood Sugar Considerations
For anyone monitoring blood sugar, prune juice requires careful portioning. At 42 grams of sugar per cup, it can cause a rapid glucose spike, particularly because liquid sugar absorbs faster than sugar from solid food. The sorbitol content slows this slightly, but not enough to make a full glass a low-impact choice.
Carbohydrate counting guides classify just one-third of a cup of prune juice as a full carbohydrate serving (15 grams). That means a standard 8-ounce glass counts as roughly three carbohydrate servings, which is significant for anyone tracking intake. If you need the digestive benefits, starting with the smallest effective dose and monitoring your response is the practical approach.