Fueling Your Body

This is part two in our nutrition series. You can read part one here

In the previous blog post we looked at nutrition from a bird’s eye view, covering the role of vitamins, minerals and macro and micro nutrients. In today’s post, we’ll zoom in a bit closer and learn how the body actually fuels itself. Having a basic understanding of how we turn food into fuel that then powers our cells will continue to build upon our nutrition foundation so we can better assess health claims as well as know what we should be putting into our bodies.

The Stuff of Life

Cells need energy to function. Luckily with a little bit of food and oxygen they're able to make all the energy they need in the form of ATP (adenosine triphosphate). Assuming appropriate macronutrient intakes, as soon as you eat a meal, your body goes to work converting that delicious Fresh Kitchen bowl of goodness into usable energy. As we learned in our last post, this entire process is known as metabolism. To make ATP, our cells crave a simple sugar known as glucose, which it derives primarily through the digestive process of breaking down carbohydrates.

Your body is a creative machine and has multiple ways to create energy for itself depending on the circumstances. For intense bouts of exercise lasting no more than two minutes, your body uses free standing glucose in the blood stream or it breaks down stored muscle and liver glycogen (name for stored glucose) via a hormone called glucagon, which is released from the pancreas.

Energy Without Oxygen

Once glucose is shuttled into the the cell, the process of anaerobic glycolysis begins. During glycolysis, glucose is broken down or metabolized into a substance called pyruvate through a series of steps. As oxygen is limited, the body temporarily converts pyruvate into a substance called lactate, which allows glucose breakdown and thus energy production to continue. The working muscle cells can continue this type of anaerobic energy production at high rates, during which time lactate can accumulate to high levels.

While the lactic acid system is quick, it’s not very efficient. The output is 2 ATP molecules for every one molecule of glucose. A naive person might think this sounds like a great deal (2 for 1) but in reality it represents 5 percent of glucose’s energy potential (38 ATP) which occurs during aerobic glycolysis (Krebs Cycle), which we’ll talk about shortly.

A side effect of high lactate levels is an increase in the acidity of the muscle cells, along with disruptions of other metabolites. The same metabolic pathways that permit the breakdown of glucose to energy perform poorly in this acidic environment. On the surface, it seems counterproductive that a working muscle would produce something that would slow its capacity for more work. In reality, this is a natural defense mechanism for the body; it prevents permanent damage during extreme exertion by slowing the key systems needed to maintain muscle contraction. Once the body slows down, oxygen becomes available and lactate reverts back to pyruvate, allowing continued aerobic metabolism and energy for the body’s recovery from the strenuous event.

Fun fact: lactate or, as it is often called, lactic acid buildup is not responsible for the muscle soreness felt in the days following strenuous exercise. Rather, the production of lactate and other metabolites during extreme exertion results in the burning sensation often felt in active muscles. This often painful sensation also gets us to stop overworking the body, thus forcing a recovery period in which the body clears the lactate and other metabolites.

Energy With Oxygen

As eluded to above, the body has a much more efficient way to create ATP when oxygen is readily available (read, when you’re not doing Fran). This process is known as aerobic glycolysis and the glucose molecule, which has been converted to pyruvate is ushered into the Krebs Cycle (aka the citric acid cycle). While this process takes longer, it’s much more efficient, resulting in 38 ATP molecules. Also, it’s important to note the difference in macronutrients used for fuel between the two systems. In anaerobic glycolysis, carbohydrates are the primary fuel source, while aerobic glycolysis relies on fat via the breakdown of triglycerides into glucose.

Why two different systems to create energy, especially when one system is much more efficient? Well, it’s theorized that once upon a time when our planet was still in its infancy, oxygen in the atmosphere was much less present than it is today. For our ancient organisms, having an anaerobic process for creating energy was a necessity for survival.

Moving Forward

Now that we have a basic understanding of how cells generate energy to function we can already see the importance of carbohydrates and fats in our diets. Carbohydrates are especially important for CrossFit athletes because we focus on short, intense bouts of exercise. With low carbohydrate levels, we actually rob ourselves twice. First, by not having readily available fuel to power us through the workout and then again with recovery as our body will start to break down muscle to convert amino acids into fuel.

While we still haven’t outlined what we should be eating, understand that both carbs and fats are not dirty words. If we’re concerned with athletic performance then having the appropriate amount of each in the diet is essential to keep the gainz coming.

In our next post we’ll delve into how our bodies actually manage our blood sugar levels to ensure we always have enough energy for the tasks at hand. Additionally, we explore why electrolytes are so important and how they deliver nutrients into our cells. Finally, we’ll bring all these concepts together to derive what we should be eating pre and post workout to deliver the best results.

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