Just as you would not begin a long road trip without gassing up your car, exercising with the needle on empty will not get you very far in terms of reaching your fitness goals. Understanding how your body uses food for fuel both during and after exercise will help you make optimal nutrition choices to power through your daily routine.
Fuel for Exercise
Physical performance requires calories from food for energy. But calories alone will not satisfy the demands placed on your body during exercise. The type and quality of nutrition you ingest each day determines how your body performs and functions throughout the day. While you can push a poorly nourished body through an exercise routine, inadequate stores of glycogen will diminish exercise quality and intensity, and inadequate dietary vitamins and minerals will interfere with energy production. If your goal is to lose weight, you will burn more calories during exercise when you eat a balanced diet of nutritious whole foods.
Carbohydrate and Energy
During resistance and high-intensity training and in the early phases of cardiovascular endurance training, your muscles rely heavily on carbohydrate for repeated contraction. Carbohydrates are plant-based foods that are broken down to glucose in the body and stored in the muscles and liver in the form of glycogen. Once you have reached your storage capacity, excess carbs are converted to fat and stored in the adipose tissue. Consistent exercise enhances your capacity to store glycogen while reducing your fat stores. To maintain high energy levels and help the muscles recover from exercise, glycogen stores should be replenished shortly after exercise. A 2007 study presented at the American College of Sports Medicine Annual Meeting showed whole-grain cereal with milk to be highly effective for replenishing post-workout glycogen.
Fat and Energy
Fat is an important storage fuel for daily and long-duration activities. While energy from carbohydrates is released quickly during exercise, fat is a slow-burn aerobic fuel that requires the presence of oxygen in the cells. During prolonged rhythmic exercise, your body taps into fat stores only after glycogen stores become depleted, about 20 minutes or so after you start working out. The good news is that regular endurance training enhances your ability to use fat during exercise. According to exercise physiologist Pete Fitzinger, endurance training increases the capillaries that carry oxygen to the cells, increases the myoglobin that carries the oxygen to the mitochondria in the muscle cell, and stimulates the growth of more and bigger mitochondria in the cells that produce aerobic energy from fat.
The Role of Protein
In the absence of adequate glycogen stores, protein is a potential source of fuel during prolonged activity, but it must first be broken down into amino acids and then converted to glucose. While not a prime source of fuel, protein is necessary for muscle growth and repair and oxygen transport. Muscle tissue is metabolically active, meaning it contributes to your total daily energy expenditure. Muscular bodies burn more calories all day long, making them less likely to store food as fat and making weight loss easier. Resistance training coupled with aerobic endurance training enhances the use of food for fuel by boosting muscle mass and increasing the use of fat for fuel.
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