Why fruit juice can raise blood sugar quickly
The beverage is fruit juice, such as orange juice. Juice contains sugars naturally present in fruit, but pressing fruit removes most of its fiber—the part that slows digestion and helps keep sugars enclosed in the fruit’s structure. With little chewing and little fiber to slow it down, juice can leave the stomach and deliver sugar to the bloodstream relatively quickly.
That speed matters: blood glucose can rise sharply, prompting the body to release insulin to move glucose out of the blood and into cells. A glass can also contain the juice of several pieces of fruit, making it easy to take in more sugar than you might eat as whole fruit.
Why the donut comparison isn’t universal
A donut is not a low-sugar food. But its fat, and sometimes protein, can slow stomach emptying, so its glucose rise may be less rapid than juice’s in some comparisons. That does not make the donut healthier, or mean juice always produces a bigger spike. Portion size, the type of juice, what else is eaten, and individual differences all affect the response.
The practical distinction is whole fruit versus fruit juice: whole fruit keeps its fiber and takes longer to eat. Juice can still fit into a diet, but treating it as interchangeable with an intact piece of fruit overlooks how quickly its sugars are consumed.
