The state of Ketosis is achieved through the use of either a low carbohydrate diet or in a state of starvation. Essentially your body has been restricted in glucose containing carbohydrates; glucose is your bodies primary fuel source for long enough to need to resort to alternative sources of fuel. In this case Ketone bodies, a byproduct of the breakdown of fatty acids, are used as an alternative to carbohydrates. Accordingly id your body is relying on ketone bodies for its energy needs it is in a state of ketosis. Low Carbohydrate diets rely on your bodies ability to use ketone bodies for energy by burning burn excess body fat for fuel.
Sugar and Ketosis
Table sugar, or sucrose, is a six carbon disaccharide containing one molecule of glucose and one molecule of glucose. Ingesting sugar in sufficient quantities, the amount varies depending on your body type and activity levels will stop ketosis as your body now has a supply of glucose to fuel it.