How Do Ketogenic Diets and Ketosis Cause Weight Loss?

by Dr Sam Girgis on September 7, 2012

Human physiology is designed to use three different types of molecules for our energy requirements.  Carbohydrates, fats, and proteins can be used to sustain the normal metabolic activities required for human life.  Carbohydrates will be used preferentially before both fats and proteins.  The most basic of carbohydrate molecules is glucose, and the body obtains glucose from the diet or through breakdown of glucogen stores in the liver, a process termed gluconeogenesis.

When carbohydrate levels are low (as in low carb diets), the body will then turn to metabolizing or burning fat for its energy requirements.  This fat can come from either our diet or from fat store in our adipose tissue.  Finally, when both carbohydrates and fat are not available, the body will begin to utilize protein from either the diet or its own muscles.  This can occur during a period of starvation in an individual with little fat stores on their body.

When the body uses carbohydrates for energy, the final energy molecule is glucose.  When fats are used for energy, the body burns fatty acid molecules (stored in fat cells) into smaller molecules called ketones.  Low carbohydrate diets, also termed ketogenic diets or low carb diets, work by causing the body to switch from using glucose as the primary energy source to ketones as the primary energy source.  When this occurs, the body switches from burning carbohydrates for energy to burning fat for energy.  At the same time, the body will begin to burn the fat stores and weight will be lost.

When ketones are being used as the energy source by the body, metabolism is in a state of ketosis.  It is important to distinguish ketosis from ketoacidosis.  Ketosis is a normal physiological response to either a low carbohydrate state or a period of fasting when food may be less available.  Ketoacidosis is a pathological state that can be life threatening and occurs during diabetic ketoacidosis.  Type 1 diabetics or insulin dependent type 2 diabetic can go into a state of ketoacidosis.  In addition, alcoholics and individuals going through starvation can go into states of alcoholic ketoacidosis and starvation ketoacidosis, respectively.

The ketosis that ketogenic diets cause is not a pathological condition.  It is more of a metabolic adaptation that normal human physiology uses to utilize different types of energy sources.  A good analogy would be the difference between a campfire and a blazing housefire.  The camp fire (ketosis) is a low grade controlled event, while the house fire is an uncontrolled destructive process.

The key to remember is that ketosis will cause the body to use fat as an energy source and thus burn the fat on your body so you can lose weight and become “cut” like a well trained bodybuilder.

In a future post, we will discuss the safety of ketogenic diets and the state of ketosis that they cause.

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