You don’t have to look far to find an article, a blog, or a social media post about nutrition. Nutrition is well understood when you consider where and how food is processed in the body.
However, from an athletic performance standpoint, there are two questions to be answered. We need to know what we must consume and when. We will be writing a series of blogs diving deeper into fitness and nutrition. We’ll begin with the different energy sources our body can use and how they get used.
Important Sources of Energy for Exercise
Carbohydrates are the body's preferred source of energy, and they are stored in the muscles and liver as glycogen. When you exercise, your body breaks down glycogen to release glucose, which is then used for energy.
Fats are also a source of energy, but they are not as easily used by the body as carbohydrates. Fats are stored in the body as triglycerides, and they are broken down into fatty acids and glycerol. The fatty acids are then used for energy, and the glycerol is used to make glucose.
Protein is not a primary source of energy for exercise, but it can be used for energy if there are not enough carbohydrates or fats available.
There are two main physiological energy pathways the body uses for exercise:
Aerobic (with oxygen): energy pathways use oxygen to produce energy, and they are used for long-duration, low-intensity exercise.
Anaerobic (without oxygen): energy pathways do not use oxygen to produce energy, and they are used for short-duration, high-intensity exercise.
The type of workout you do will determine which energy pathway your body uses. For example, if you are doing a long run, your body will use aerobic energy pathways. If you are doing a short sprint, your body will use anaerobic energy pathways. With short-duration exercise, the body doesn’t need to replenish energy.
However, in long-duration exercises, the body has to keep making more energy while it’s working, thus requiring oxygen to complete the chemical reaction. Before you take a big lift you take a deep breath and brace, exhale and maybe take one more breath. All the oxygen needed for the lift is present and accounted for, but after a heavy lift, you may huff and puff for a while.
3 Main Forms of Carbohydrates
*All forms have their own characteristics and purpose.
Monosaccharides are single sugar molecules that cannot be broken down any further. Examples of monosaccharides include glucose, fructose, and galactose.
Monosaccharides are primarily utilized in the body's aerobic energy system, which is also known as aerobic metabolism. This energy system requires oxygen to convert glucose into adenosine triphosphate (ATP), the energy currency of the body's cells.
During aerobic metabolism, glucose is broken down through a series of chemical reactions in the presence of oxygen to produce ATP. This process occurs in the mitochondria of cells and is a highly efficient way of producing energy. It is the primary energy system used during endurance exercise or any activity lasting longer than a few minutes.
However, monosaccharides can also be utilized in the body's anaerobic energy system, which is also known as the glycolytic energy system or anaerobic metabolism. This energy system does not require oxygen but is less efficient than aerobic metabolism in producing ATP. During anaerobic metabolism, glucose is broken down into ATP and lactic acid. This is the primary energy system used during high-intensity, short-duration activities like sprinting or weightlifting. This is also why lactic acid buildup (soreness) is so prevalent in high-intensity, short-duration sports.
Monosaccharides are primarily broken down in the small intestine of the body. When we eat foods that contain carbohydrates, enzymes in the saliva, stomach, and small intestine break down the carbohydrates into their individual sugar molecules. Once broken down, they are absorbed into the bloodstream and transported to cells throughout the body to be utilized for energy.
The speed at which monosaccharides can be utilized after ingestion depends on several factors, including the type of monosaccharide, the presence of other nutrients in the meal, and individual differences in digestion and metabolism. Glucose, for example, is rapidly absorbed into the bloodstream and can be utilized by cells for energy within minutes of ingestion. Fructose (usually from fruit), on the other hand, is absorbed more slowly and must first be metabolized by the liver before it can be utilized by other cells in the body.
In general, simple carbohydrates like monosaccharides are quickly broken down and absorbed into the bloodstream, which can cause a rapid increase in blood sugar levels. This is why consuming too much sugar or refined carbohydrates can lead to a "sugar high" followed by a crash.
Complex carbohydrates like starches, on the other hand, take longer to break down and can provide a more sustained source of energy. Complex carbohydrates are not the same as monosaccharides, as they are larger and contain multiple molecules of sugar in a single chain. This is why “carbo-loading” was so popular and still is. It provides long-lasting supplies of carbohydrates.
Taking one step up in chemical complexity, we arrive at . As you might guess from the name, these are two sugar molecules bonded together. Examples of disaccharides include sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose).
Disaccharides are broken down in the small intestine by specific enzymes called disaccharidases. These enzymes break the chemical bond between the two sugar molecules, releasing the individual monosaccharides. For example, lactose (a disaccharide) is broken down by the enzyme lactase into its two component sugars, glucose, and galactose.
The monosaccharides released from disaccharides can then be absorbed into the bloodstream and utilized for energy by cells throughout the body. Like monosaccharides, the speed at which disaccharides are utilized after ingestion depends on several factors, including the type of disaccharide, the presence of other nutrients in the meal, and individual differences in digestion and metabolism.
Disaccharides are primarily utilized in the body's aerobic energy system, which requires oxygen to convert glucose and other sugars into ATP. The breakdown of disaccharides into their component monosaccharides allows for more efficient utilization of the sugars in this energy system.
The speed at which disaccharides are utilized after ingestion can vary depending on the type of disaccharide and other factors. For example, sucrose (table sugar) is rapidly broken down into its component monosaccharides (glucose and fructose) and absorbed into the bloodstream, leading to a quick rise in blood sugar levels.
Lactose, on the other hand, can be more slowly digested by some individuals who are lactose intolerant and do not produce enough lactase enzyme to break down the lactose. Lactose is also broken down more slowly than other sugars because of its size. This can lead to digestive symptoms such as bloating, gas, and diarrhea.
Finally, we have polysaccharides, long chains of sugar molecules such as starch, glycogen, and cellulose. Starch and glycogen are used by plants and animals, respectively, to store energy, while cellulose is a structural component of plant cell walls and cannot be digested by humans. Polysaccharides are broken down in the body, mainly in the small intestine, by enzymes called amylases that break down the chains of glucose molecules, which can then be absorbed into the bloodstream and used by cells for energy.
The speed at which polysaccharides can be utilized after ingestion varies depending on several factors, as stated above. Polysaccharides like starches are broken down more slowly than simple sugars like monosaccharides and disaccharides, providing a slower and more sustained source of energy. The rate of digestion and absorption of polysaccharides can also be influenced by factors such as food processing, cooking methods, and the presence of fiber in the meal.
Fiber can affect the absorption of polysaccharides in several ways. First, fiber reduces the rate at which carbohydrates, including polysaccharides, are broken down and absorbed in the small intestine because it slows down the movement of food through the digestive system. As a result, the absorption of glucose and other sugars from polysaccharides can be slower and more gradual, leading to a slower and more sustained release of energy.
Second, fiber can increase the bulk of the meal and promote a feeling of fullness, which can help regulate appetite and prevent overeating. This can be particularly important for individuals who are trying to manage their blood sugar levels, as consuming too many carbohydrates too quickly can cause a rapid spike in blood sugar levels followed by a crash.
Third, some types of fiber also act as prebiotics, feeding the beneficial bacteria in the gut. These bacteria can then produce short-chain fatty acids (SCFAs), which can be used as an energy source by the body's cells. This process can provide an additional source of energy and help support gut health.
Now that we’re up to speed on how food is broken down and used for energy, in an upcoming blog post, we’ll explore what foods you should eat depending on your training goals. As always, if you have questions, comments, or anything else, please comment below and get the discussion rolling.
And don’t forget to follow us on social media @deepathletics.
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