One prune will typically contain between 20 and 25kcal, with the vast majority of the energy from sugars.
It contains very little protein, and even less fat. These sugars are easily available for your body, but are released progressively. These qualities are highly prized by sportsmen and women who participate in high and medium intensity sports, thanks to the ideal balance of glucose, fructose and sorbitol; in other words, they offer the right balance of quickly and slowly assimilated sugars.
This balance gives prunes a moderate glycaemic index of 52.

Glucose is a monosaccharide which is assimilated extremely quickly, and is burned up by your metabolism. This is the standard “fuel” for your body’s cells.

Fructose is a monosaccharide which is characteristically found in fruit, and which affects your body’s glycaemic regulation. Once metabolised by the liver, it is transformed into glucose and can then be used to power your muscle contractions.

Sorbitol is not a sugar that is often found in plants (it takes its name from the French word for rowan). Agen prunes, with an average sorbitol content of 10g per 100g (sometimes ranging from 3g to 20g), are one of the fruits which contain the most. A polyol with a slightly different chemical structure to other sugars, sorbitol is not as sweet as glucose or fructose. It is only partially digested by your small intestine, and then only partially metabolised in your colon. It has only a minor effect on your blood sugar and insulin levels. Lastly, sorbitol acts as a stimulant for your gallbladder and your intestines.
The sorbitol content of fruit (per 100g net of fruit)