Aristotle said it best: “The energy of the mind is the essence of life.” Although he may not be talking about the energy that we, as gym-goers, are burning in the gym, it is safe to say that the words of the Greek philosopher are a good base for my entire discussion today. Allow me to explain.
Within the body, there are countless chemical reactions taking place every single second, most of which requiring a source of energy. As you move your eyes along your screen, as you inhale and exhale and as I move my fingers along this keyboard, energy is being used in the form of adenosine triphosphate, or ATP. ATP is the body’s fuel, and without it… well, let’s just say you would not be reading this article. Now, if energy is being burned as you read what is on your screen, you better believe that in the gym, the body uses and requires a very large amount of it.
What does this have to do with carbohydrate?
When we generate energy, we are taking nutrients and converting them into ATP. This process, otherwise known as energy metabolism, differs from macronutrient to macronutrient, as does the amount of energy from each. Dietary fat contains 9 kcal/g, making it the highest energy-yielding macronutrient, while protein and carbohydrate provide 4 kcal/g. We can see here that all macronutrients provide energy, but the difference lies within the pathway that each follows. Upon ingestion, carbohydrates are converted to monosaccharides, including glucose, fructose and galactose. Fructose will make its way to the liver, whereas galactose (as UDP-glucose) and glucose will travel along the glycolytic pathway—a process known as glycolysis (you may have heard about this in your high school science class.) Glycolysis takes this sugar (glucose) and through a series of reactions, forms pyruvate. Pyruvate then enters the citric acid cycle (TCA cycle) and produces energy to be used by the body. What does this all mean? It is just a scientific way of saying that carbohydrates are easily converted into usable energy.
If no carbohydrate is present, though, the body must look elsewhere to form glucose. Where will it look? It will begin to use other sources, such as fatty acids and glucogenic amino acids coming from the amino acid pool and muscle tissue. This process is known as gluconeogenesis, which is the formation of glucose from non-carbohydrate sources. It is a very demanding process, forcing the body to catabolize stored energy and potentially lean muscle, which is exactly what we do not want. Carbohydrate acts to inhibit this by promoting glycolysis and opposing gluconeogenesis.
Going off of this, it is important to note that carbohydrates have a direct effect on insulin levels. This also assists in the maintenance of lean muscle. Since insulin is anti-catabolic and prevents tissue breakdown, it will leave amino acids for storage and/or protein synthesis. When speaking in terms of fat loss, it is important to understand that high levels of insulin will impair fatty acid metabolism. However, if one is in a caloric deficit at the end of the day, insulin levels will decrease and fat oxidation will take place, leading to weight loss.
What about carbohydrate vs. fat or protein as a source of energy for exercise?
We already discussed gluconeogenesis. The end product of gluconeogenesis is glucose, and if you remember from the beginning, carbohydrate enters the bloodstream as glucose; there is no need to convert it. So, in terms of energy production, carbohydrates are much more efficient than both fat and protein. In addition to being more-readily converted to glucose, protein metabolism requires extra ATP to excrete its nitrogen group and maintain a positive nitrogen balance. This gives it a higher thermic effect, but makes it a suboptimal form of energy.
Now, when rates of fatty acid degradation are high, the liver begins to produce molecules known as ketone bodies. Ketone bodies can be used as energy for exercising muscle, the brain and other peripheral tissues. In short, ketone bodies can take the place of glucose. This causes a “metabolic shift” and forces the body to no longer relies on glucose, but now relies on ketones. However, some cells cannot use them, such as red blood cells, because they lack a mitochondrion, and the liver because they lack the proper enzymes. Most of the tissues that CAN use ketones still prefer glucose.
Finally, the last important thing to note when discussing carbohydrate as an energy source as opposed to the other macronutrients is the fact that glycolysis can take place without the presence of oxygen; it is an anaerobic process. Since the muscle contains its own glycogen bank, it can release some for energy production very efficiently. This means that in times of metabolic stress, which in our case, is high-intensity exercise (when oxygen levels are low), carbohydrate is used directly as the body’s source of energy.
Sources of Carbohydrate
Now we can discuss sources of carbohydrate. I can sit here and make a list of foods that I tend to consume on a day-to-day basis, but I think it is best to explain what groups of foods contain carbohydrate, and then give some examples of each. The first thing that comes to mind when discussing carbohydrate is the grains group, which includes bread, pasta, cereal, rice, oatmeal, quinoa and most snack foods. I am an advocate for whole grains because of their fiber content, but as long as the foods fit within your daily caloric requirements, they can be refined (just try to keep this under control; moderation is key.) Next would be the starchy vegetables, such as white, red, sweet and gold potatoes, and also corn. Wrapping up the primary sources of carbohydrate, we have fruits, along with any food that contains a mild-to-moderate amount of sugar.
Foods that contain a very low amount of carbohydrate are known as the non-starchy vegetables. The bulk of this group of foods is made up of the leafy greens, such as spinach, kale and lettuce. Also included are mushrooms, broccoli, peppers, asparagus and cauliflower. Most non-starchy vegetables are very rich in fiber. Fiber is very important to digestive health and can help in curbing appetite. They add bulk to food and are not absorbed in the intestine. (There are also foods high in protein and/or fat that contain very little carbohydrate, such as nuts and meats, but I am only discussing foods known as carbohydrate sources.)
That brings me to my final topic—net carbs. A lot of people tend to think that because fiber is not absorbed, it can be subtracted from the amount of carbohydrates in a food, giving a “net carb” amount. It is thought that carbohydrates from fiber do not enter metabolism, meaning that they do not provide energy and have no effect on blood sugar. Well, a spike in blood sugar is not going to have a lasting, negative effect on a healthy individual in regards to weight loss/gain anyway; it will only play a role in level of satiety, so disregard that. As far as energy value goes, fiber is fermented by bacteria within the gut, so the notion that fiber is not absorbed and therefore, its calories do not count almost makes sense. Fact of the matter is, something in the body is utilizing that energy, so it does count.
In short, the conversion of carbohydrates to glucose is significantly more efficient than that of the other macronutrients. Their effect on insulin can help inhibit the loss of muscle mass, while not negatively impacting fat loss when in a caloric deficit. Lastly, we were able to discuss sources of carbohydrates and fiber, along with why it is essential to overall health, how it helps satiety and why its calories DO count.
I may not be on Aristotle’s level, but I will say that the energy of the muscle is the essence of growth!
*Disclaimer: I am not a doctor or dietitian and do not claim to be. All recommendations made are based off of my personal experience and knowledge and is not intended to treat or cure any serious medical conditions.
1. Harvey R, Ferrier D. Lippincott’s Illustrated Reviews: Biochemistry 5th Edition. Philadelphia, PA/Baltimore, MD: Wolters Kluwer Health, Lippincott Williams and Wilkins. 2011. p. 91-105 2. Veldhorst MAB, Westerterp-Plantenga MS, Westerterp KR. Gluconeogenesis and energy expenditure after a high-protein, carbohydrate-free diet. In: Am J Clin Nutr. September 2009; vol. 90 no. 3, 519-526 3. Chow LS, Albright RC, Bigelow ML, Toffolo G, Cobelli C, Nair KS. Mechanism of insulin’s anabolic effect on muscle: measurements of muscle protein synthesis and breakdown using aminoacyl-tRNA and other surrogate measures. In: Am J Physiol Endocrinol Metab. October 2006; vol. 291 no. 4 E729-E736. 4. Weiner D, Mitch WE, Sands JM. Urea and Ammonia Metabolism and the Control of Renal Nitrogen Excretion. In: Clin J Am Soc Nephrol. 2015; vol. 10 no. 8 5. Rand WM, Pellett PL, Young VR. Meta-analysis of nitrogen balance studies for estimating protein requirements in healthy adults. In: Am J Clin Nutr. January 2003. vol. 77 no. 1, p. 109-127 6. NouNou H. Ketogenesis and Ketolysis. In: King Saud University College of Science, Biochemistry Department. 7. Harvey R, Ferrier D. Lippincott’s Illustrated Reviews: Biochemistry 5th Edition. Philadelphia, PA/Baltimore, MD: Wolters Kluwer Health, Lippincott Williams and Wilkins. 2011. p. 195-6 8. Crittenden R, Karppinen S, Ojanen S. In vitro fermentation of cereal dietary fibre carbohydrates by probiotic and intestinal bacteria. In: J Sci Food Agric. 2002. 82:781-789.