Your body’s primary source of energy should come from the burning of fat.  Sugar, or carbohydrates, should only be used for energy when blood sugar levels are high, during intense exercise, or when the body cannot access fat stores.  In order to lose fat, your body needs to burn fat rather than sugar as your body’s primary source of fuel.  

On an average day, the body burns a mixture of fat and carbohydrates with a small amount of protein.  Ideally, a person should only burn fat while at rest because the activities where the body burns sugar (high blood sugar levels, intense workout, and inability to access fat stores) should not be activated.  Unfortunately, many people burn carbohydrates at rest because of elevated levels of blood sugar and insulin in their body.  As a person consumes food or activity increases, the percentage of fat burned and the percent of carbohydrates increase. 

An individual can measure how their body metabolizes carbohydrates and burns fats during exercise and rest through metabolic testing.  If a person’s lifestyle leads the body to metabolize more glucose than fat, it will not be able to burn a sufficient amount of stored fat to help them lose weight even if they are on a low-calorie diet.  For example, a 1200 low-fat, high-carbohydrate diet is recommended for women who believe weight loss is about calorie counting.  In theory, a woman who burns 2200 calories will have to make up a 1000 calorie deficit and it will all come from stored fat.  In practice, the body will make up the energy deficiency by doing the following:

• Burning the available glucose and stored glycogen
• Breaking down muscle tissue and converting it to glucose
• Increasing appetite to the point where it’s difficult to not eat more than 1,200 calories
• Reduce the metabolic rate to reduce energy expenditure

The body’s supply of glucose is limited and as glucose levels fall, protein from muscle must be converted into energy.  Diets that rely on glucose over fat lead a person to irritable of fatigued just a few hours after eating.  The rising and falling of blood sugar levels is an obvious sign of excessive carbohydrate consumption, and these feelings are amplified by restricting calorie consumption.  In the end, people do lose weight from counting calories from carbohydrate heavy calorie counting, but the weight loss comes from muscle and the fat remains.