First, lets review some key words so all of this science makes sense. Bioenergetics is the study of energy in the human body. Since we need energy to sustain life, exercise, and recover from it, this is kind of important! Metabolism refers to all of the chemical reactions that occur in the body to maintain itself. It is the process in which nutrients are acquired, transported, used, and disposed of by the body. Exercise metabolism is the relation of bioenergetics to the physiologic changes and demands placed on the body during exercise. Energy. The main energy sources are carbohydrates, fats, and proteins (AKA Macros). Phew, onto the Macros…
Fuel for Energy Metabolism
When we eat food, it has to be further broken down into substrates before it can be used for energy. Carbs, fats, and proteins are the main substrates used to transfer energy to the cells.
Macronutrient #1 Carbohydrates. Carbohydrates are not just bread, bagels, or pasta. Carbohydrates are not the devil either. Carbohydrates are organic compounds of carbon, hydrogen, and oxygen, which include starches, cellulose, and sugars. Carbohydrates are a good source of fuel for the body during daily activities and exercising. Lack of carbs in the diet can cause fatigue, poor mental function, lack of endurance, and lack of stamina. Hang out with someone on a low carb diet and tell me how friendly they are after the third day. Once carbs are digested they produce glucose (a simple sugar). Glucose is then absorbed and transported in the blood where it circulates until it enters the cell, from there it is either used or stored as energy. Once it is stored it is known as glycogen. Glycogen is a string of glucose molecules that can be broken down and used for energy, especially during long intense exercises. Glycogen is stored in the liver and in the muscles.
Macronutrient #2 Fats. Eating fat will not make you fat… promise. Fat helps the body use vitamins and keeps skin healthy. They are also a great energy source. Triglycerides are the chemical or substrate form in which most fat exists in food as well as in the body. When excess calories are consumed they are converted in the body as triglycerides and transported to fat cells. Most people have a decent supply of fat, which can be broken down into triglycerides and used for energy (enter the Keto Diet hype).
Macronutrient #3 Protein. The beloved protein. Brotein. The bodybuilders BFF. Protein doesn’t actually supply much energy during exercise and isn’t a significant fuel for energy metabolism. Protein only becomes a significant source of fuel when the body is in starvation. If calories are restricted too much amino acids are used to form glucose, this is known as gluconeogenesis.
Energy During Exercise
Intensity and duration of exercise are inversely related. Immediate energy systems are for a very short-duration exercise, here, the main fuel source is stored ATP (adenosine triphosphate) and phosphocreatine. When the duration increases (longer than 2 minutes) the main fuel source becomes glucose. When the duration increases even longer, the main fuel source becomes glucose AND fat. After 90 minutes of exercise glycogen stores are basically depleted. When glycogen is used up, the fuel source switches over to fat. Long story short, energy from ATP is limited, energy from carbs (glycogen) is limited, but energy from fat is almost unlimited. Your body needs energy for exercise. Your body needs the correct ratio of carbs, fats, and proteins to function optimally. If you’re overwhelmed by all this crazy science, you’re not alone. There are many personal trainers and dietitians that are able to provide you the correct Macro Ratios to match your goals.