Milo contains 1,680 kJ (402 calories) in every 100 g of the powder, mostly from carbohydrates, mainly sugar. Carbohydrates can be used for energy by the body, which is the basis of Milo being marketed as an energy drink.
Milo dissolved in water has a Glycemic Index (GI) of 55, the same as Coca-Cola.
However, milk has a much lower GI of 30 - 33, so mixing a very small amount of Milo into a mug of milk yields an overall GI closer to 33, and mixing a large amount of Milo into a mug of milk will give a GI closer to 55.
The Milo website states that the drink is high in calcium, iron and the vitamins B1, B2, B6, B12. Milo is advertised as containing "Actigen-E", but this is just Nestlé's trademarked name for the vitamins in the Milo recipe.
Milo contains some theobromine, a xanthine alkaloid similar to caffeine which is present in the cocoa used in the product.