What is a low carbohydrate diet?

Low carbohydrate diets (or low carb diets) are dietary programs that limit the amount of carbohydrates consumed to between 50 to 75 grams per day (or less) depending on the type of low carb diet and health requirements of the individual.

All low carb diets restrict the intake of both simple carbohydrates (i.e., carbs that are made of simple sugars that are absorbed quickly such as refined sugar products) and complex carbohydrate containing foods that are usually high in starch such as grains, cereals, certain ‘starchy’ vegetables, legumes and others that have a high glycemic index (GI) and can cause a rapid rise in blood glucose levels.

To obtain sufficient macronutrient and caloric intake from food, low carbohydrate diets tend to contain higher relative proportions of protein and fats. For this reason they are often referred to as ketogenic, paleo or low carbohydrate-high fat (LCHF) diets due to their ability to cause ketosis (or ketogenesis) in the body, a process that occurs in the liver and produces ketone bodies which can be used as an alternate energy source to glucose.

Typically, glucose is derived from digested carbohydrates and is regulated by the hormone insulin that is produced in the pancreatic beta cells and secreted in response to glucose in the blood stream. Insulin is an important regulator of carbohydrate, fat and protein metabolism. It is responsible for the cellular uptake of glucose from the bloodstream into skeletal muscles, the liver and fat tissue. The primary actions of insulin are to activate pathways in the body that store energy derived from carbohydrates, i.e., to:
• Promote glycogen synthesis in the liver and muscle cells), whilst simultaneously
decreasing gluconeogenesis (the production of glucose from non sugar substrates);
• Increase fat synthesis (lipogenesis) in adipocytes (fat cells) to form triglycerides and to decrease lipolysis which reduces the conversion of fats stored in adipocytes into fatty acids.

When there is a scarcity or absence of dietary carbohydrates, less glucose enters the bloodstream, thus less insulin is secreted which leads to reduction in lipid synthesis and fat accumulation. The body is then forced to find alternate energy sources in the form of ketone bodies.

Physiological ketosis which occurs during very low carbohydrate diets or prolonged fasting is different to diabetic ketoacidosis which occurs primarily in patients with type 1 diabetes from a lack of insulin and the metabolic consequences associated with this shortage.