You might think that since fruit juices come directly from the fruit, then they should be equivalent to the fruits themselves in terms of nutritional values.
However, fruit juice is generally no healthier than the fruit itself. Even if the juice is freshly squeezed, drinking the juice is less healthy than eating the fruit itself. There are two main reasons for this discrepancy.
First, the husk and skin of the fruit left behind are rich in dietary fiber. Dietary fiber plays a more important role than simply regulating the digestive system. When you eat a whole fruit, the dietary fiber in the pulp binds to the natural sugar in the fruit and ‘circulates’ through your gastrointestinal tract.
This binding action makes it harder and requires more time for your body to absorb the sugar. As a result, fruit sugar accumulates in your bloodstream at a slower and slower rate if you eat whole fruits than if you drink fruit juice directly.
This process allows your body to use more sugar as a direct source of energy. In contrast, drinking fruit juices leads to an increase in blood sugar. Feeling you have more sugar than you need, your body quickly releases insulin, causing a large amount of sugar in your blood to be converted to fat and glycogen.
This way, the rise in blood sugar leads to a drop in blood sugar (unless more food is eaten), leaving you hungry again. And being hungry makes you eat more. In this way, drinking pure fruit juice leads to poorer blood sugar regulation and increased calorie intake, compared to fruit consumption.
People who are particularly sensitive to blood sugar levels may also experience headaches, lethargy and irritability after drinking fruit juice, while these symptoms do not appear when eating whole fruits.