Thoughts on Carbohydrates as a Fuel Source

Why Eat Carbohydrates Anyway?

Carbohydrates are the primary source of fuel used by the body to think, to perform activities of daily life, and to exercise. They are stored in the liver and muscle as chains of glucose in large polymers called glycogen. The amount of energy stored as glycogen is about 2 % of the body’s total energy stores. Because the body does not store large amounts of carbohydrates, we have to have a handy source of them from foods and beverages to fuel our bodies. Maybe we should just strap a backpack of carbohydrates on every morning!

In a healthy person, fat stores make up 70% of the body’s energy stores, and protein stores in muscle make up approximately 25% of energy stores. The remaining energy is primarily found in blood glucose and triglycerides stored in the muscle.

Fat stores are less efficient at producing energy during exercise than carbohydrate stores. In order for fat stores to be oxidized for energy, carbohydrates must be available in the metabolic pathway that produces ATP (adenosine triphosphate) or energy. Fat stores are primarily used for fuel during light exercise like walking. During moderate exercise like jogging, stored fat provides 50-60% of the fuel for the activity. The remainder of the fuel comes from the body’s stored carbohydrates or glycogen stores.

A well-nourished person stores the equivalent of 1500-2000 calories in the form of glycogen (stored carbohydrates). Glycogen is the preferred fuel during intense exercise such as running, biking, and swimming. Since the amount of glycogen is limited in the body’s ability to store carbohydrates, this affects how long you will be able to exercise at an intense level. Even athletes in training or competition lasting more than 90 minutes load up on carbohydrates ahead of time because if they don’t, they will “bonk” or run out of energy to complete the event. These athletes also consume more than half of their calories as carbohydrates on a daily basis to maintain glycogen stores.

In the absence of glycogen, the body will burn protein from muscle stores to produce glucose in order to provide fuel to the brain and to the red blood cells which carry oxygen to all parts of the body. Muscle stores include the heart muscle and the skeletal muscles.

In a person who trains heavily for their sport or exercises compulsively due to an eating disorder, the inadequate intake of energy or the depletion of fuel sources long term may cause the loss of heart muscle and may result in heart abnormalities and a possible heart attack. This will also result in feeling fatigue and weak.

The loss of skeletal muscle will also result in the body having a lower resting metabolic rate. This is because muscle burns calories even when at rest, thus contributing to an increased metabolic rate. Fat stores do not burn calories at rest. Ultimately the more muscle mass that one has, the more calories that he/she will require to maintain his/her weight.

The right meal plan is designed to provide the optimal amount of carbohydrates needed to spare the stores of muscle in your body. Additional carbohydrates may be needed for fuel during exercise. If you do not consume enough carbohydrates before and during long periods of exercise, you may feel like bingeing on high carbohydrate foods later to restore glycogen losses to acceptable levels. Choose high carbohydrate foods wisely during the day, and you may prevent bingeing later.


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