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July 28, 2020
Carbohydrates: The World's Most Confused Macronutrient
Alright, we’ve extolled the virtues of protein, and acknowledged that fat has a valuable role as a structural molecule and fuel source. Now we dive into… DUM DUM DUM…. Carbohydrates!!!
Sometimes I think that carbs are right up there with things (like politics at the Thanksgiving table) that you just don’t talk about. It seems that everyone has an opinion on carbs, and they passionately cling to it. All carbs are bad! Carbs are the body’s preferred fuel! Sugar is the root of all evil! In order to step away from the exclamation points, we’re going to examine the role of carbohydrates in the body, carbohydrate sources, and what happens if we consume too little or too much carbohydrate.
This is a topic that I get really fired up about, because no matter how people feel about carbs as fuel, they never, ever address the fact that carbs have important structural roles in the body as well. Our connective tissue - joints, tendons, cartilage, collagen - is all composed of glycoproteins, or proteins fused with carbohydrate (glucose) molecules. This means that our strong muscles and smooth skin are just as dependent on carbohydrate availability as protein. Do you know anyone with creaky joints who supplements with glucosamine? The glucose is right there in the name - maintaining those joints requires carbs. Glucose is also a significant component of a copious bodily product, mucous. We produce mucous for more than just making allergy season unbearable and keeping Kleenex in business, it’s a vital lubricant for many body structures. Tears and saliva are both mucous-based compounds, and our lungs and guts are protected by a mucous layer. Without sufficient glucose to produce these mucous compounds, we’re at risk of “drying out” from the inside.
Glucose is a vital fuel source for our red blood cells and nerve cells (that includes your brain, smartypants!), which don’t use fat for energy. (My Keto diet friends will point out that these cells can also use ketones, and they are completely right - the body is amazing in its flexibility. Ketones and ketosis constitute a huge topic, and it will get its own post some day.) Carbs are also essential to the function of the immune system; white blood cells use the reactive byproducts of burning glucose to kill invading microorganisms. We’re always thinking and breathing, of course, but exposure to pathogens (or small children, same difference) will require additional glucose to fuel the immune response.
OK OK, I suppose carbs can do some useful things in the body after all. Now let’s get to the really controversial part of the topic, the applicability of carbs as an energy source. Unlike fat, which can only be burned when there’s oxygen available, carbs can provide energy with or without oxygen. Every single cell in our bodies is capable of burning glucose for energy, and in fact will burn glucose before fat if it’s available. Does that make it the “preferred fuel source” as some people claim? No, that means that too much free glucose floating around in the bloodstream is dangerous - ask any diabetic - and our bodies will either burn it, or store it as quickly as possible to get it under control. Glucose is stored as glycogen in the muscles, ready to fuel your next workout, but the muscles can only hold a relatively small amount. If you haven’t crushed a WOD lately and they’re full up, then that glucose is converted to fat for storage.
We already know that most of our cells can burn fat with oxygen for energy - why would we want to introduce these potentially dangerous carbs as an energy source? It comes back to crushing that WOD. Let’s take a look at this pretty graph. It shows how much of our energy is coming from fat (white and blue) or carbohydrates (black and orange) at various intensities of exercise. At the low end (chillin’ on the couch, grocery shopping) we use almost entirely fat for energy. At the mid level (playing sports, bike ride, serious hiking) fuel sources are about 50/50, and at the high end of the intensity spectrum, the majority of fuel is coming from carbohydrates. This is because energy demands are higher than the available amount of oxygen, and only glucose can provide energy without oxygen. The harder you WOD, the more carbs you need. We might as well label that “high intensity” bar BEAST MODE!!!!
So, acknowledging that carbs have both structural and fuel roles within the body, we have to ask - are those low-carb people then wrong, and we MUST consume carbs? Are carbs essential, in the way that essential fatty acids or essential amino acids are, they must come from food? Yet again, it depends. Our bodies are capable of making glucose from other sources - the liver uses the process of gluconeogenesis (literally - generate new glucose) to turn fats and protein into glucose, although it’s a slow-ish process. Also, for each unit of fat we burn for energy, a small amount of glucose is liberated as a byproduct. Our muscles and liver can store small amounts of glucose as glycogen, to be available for sudden demand. This means that, for people with efficient gluconeogenesis, who do not have large demands for glucose (immune activity, tissue repair, high intensity exercise), they do not need to consume a great deal of carbohydrates to maintain good health. These are the people who feel awesome and healthy following a low-carb diet. Other people have a greater demand for glucose than their body can supply via gluconeogenesis, and they should get carbs through their diet. If you’re constantly fighting off a cold (or have exposure to small children), recovering from injury, engaging in strength training or high intensity exercise, it’s likely that carbs in the diet will help you feel and perform better. (The best carb choices, and finding your sweet spot, will be fodder for yet another post. They sure are building up!!!)
Ultimately, it comes down to realizing that carbs are neither “good” nor “bad.” Instead, we acknowledge that they serve important roles in the body, and different people need different amounts of them to thrive Understanding how the three major macronutrients serve our health and provide fuel for our activity is a huge step towards figuring out how much of each of us should be eating to live our most awesome life.