The Atkins diet and similar low-carb weight loss plans rely on a body condition called ketosis to stimulate rapid weight loss. This physiological state is delicate to maintain, and eating even a small amount of carbohydrates -- including sugar -- can put it at risk.
Your body enters into ketosis when it is taking in too few carbohydrates. In response to this perceived starvation, it shifts your metabolism to take the bulk of its energy from fat -- especially stored fat. This is the reason low-carbohydrate diets produce such rapid fat loss. Ketosis is not all positive. Side effects include weakness, dehydration, dizziness, nausea and irritability.
Sugar is a simple carbohydrate that breaks down quickly when eaten. This fast-acting energy is the reason it tastes good. Quick energy was important for our evolutionary forebears, and our bodies still react in that way. There are many different kinds of sugar, found in fruits, breads, sweets and many processed foods.
Weight Loss Effects
If you eat too many carbohydrates on a low-carb diet, you can potentially leave a ketosis state and stop your weight loss progress. The exact maximum allowable carbs varies from diet to diet, and between different stages within the diet. However, since sugar is a carbohydrate, eating sugar is a good way to sabotage your weight loss efforts.
Sugar digests quickly and is consumed quickly for energy, creating the familiar pattern of sugar rush and sugar crash. If you haven't eaten carbohydrates for a while, these extremes may be more pronounced than usual -- leaving you feeling poorly as the sugar rush wears off. That crash can also cause sugar cravings, leading you to eat even more carbohydrates and doing worse damage to your low-carb diet.