There is a lot of discussion these days about carbohydrates, the good and the bad.  In reality, they are all related.  Carbohydrates contain carbon, hydrogen and oxygen in varied chemical relationships. 

• Sugars are the simplest of the carbohydrates and can be simple sugars such as glucose or more complex sugars. 
• Starches are strings of sugars linked together in such a way that most starches can be broken down into glucose by the action of enzymes, primarily amylase. 
• Fibers (lignin, cellulose, hemicelluloses etc.) are also chains of sugars that cannot be broken down easily by enzymes and must be fermented by the animal to release the energy. 

Starches and sugars are produced by plants as a means to store energy, so they contain energy that is more readily available than the energy in fiber.

Because horses produce less amylase, the enzyme used to break down starch, than some other animals, say perhaps pigs, they are more limited in their ability to digest large quantities of starch. However, they digest smaller quantities very efficiently and very effectively! 

Starches and sugars are a fairly concentrated source of Calories to be used as a source of energy when extra energy is required to maintain body condition and do more work.  In the wild, horses would consume seed heads (grain) when available in the fall to help them gain weight (added Calories) to be ready for winter, so starches and sugars are a part of the diet in horses in the wild.  Today’s working horse requires Calories, and a combination of fiber, starch, sugar and fat can be the best way to support the horse to maintain the balance of optimal health and optimal performance.