Hype About Carbs: Are You Getting the Entire Picture?

How many “hypes” about our diets have we experienced in the recently? – one would think – enough not to get into another one so easily. Yet, we are in the midst of a carb hype, and many of us seem to forget everything we know about metabolism. We need to agree that carbs are crucial for training and recovery, keeping cortisol levels low and testosterone high. At the same time, we should not forget what we have learned about the negative consequences of a high-carb diet (especially a diet rich in highly processed carbs) for decades. Nothing has changed, there are still those negative implications no matter how much some of the “nutrition experts” try to convince us about the benefits of chugging sugar, this knowledge can't be erased.

Carbohydrates often steal the spotlight as athletes' primary fuel, especially during endurance activities. However, the metabolic reality is more nuanced, involving a dynamic interplay between carbohydrates and fats. Understanding how these macronutrients work together can help athletes optimize their performance and endurance.

The Impact of Highly Processed Carbohydrates on Digestive Health

In the rush to maximize carbohydrate intake for peak performance, athletes often turn to highly processed ingredients such as sugars, maltodextrin, and dextrin. While these quick-digesting carbohydrates may seem like an efficient fuel source, they can wreak havoc on the digestive system. Humans are more than just moving muscle cells—there’s a complex digestive system that plays a crucial role in how well we absorb and utilize nutrients during exercise. And the digestive system do not tolerate well high concentrations of carbs, especially when they are highly processed or when their composition is limited to a single ingredient.

One major issue with highly processed carbs, particularly simple sugars, is their impact on gut permeability. When large amounts of sugar are consumed, they can cause the gut lining to become more permeable, allowing bacteria and toxins to enter the bloodstream, which leads to inflammation. This inflammation not only contributes to feelings of fatigue and exhaustion but also impairs overall performance. The digestive discomfort often accompanying high-sugar intake—such as bloating, cramping, and diarrhea—can derail even the best-prepared athletes.

In practicality, the notion of high-carbohydrate fueling is flawed. Humans are not designed to tolerate large quantities of pure carbohydrates in a short time frame. Our daily diet is composed of various nutrients, and nature has not equipped us with mechanisms to efficiently handle such high-carb inputs during exercise. The reliance on highly processed sugars, often marketed as quick fuel for athletes, ignores the body's natural limitations and can do more harm than good.

The Basics of Carb and Fat Metabolism

Carbohydrates are stored in the muscles and liver as glycogen and are the body's preferred quick energy source. During the initial phases of exercise, glycogen is broken down to glucose, which is then used to produce ATP (adenosine triphosphate), the cell's energy currency. This process is known as glycolysis.

Fat metabolism, on the other hand, involves the breakdown of fatty acids to produce ATP. This occurs through a process called beta-oxidation, which happens in the mitochondria of cells. Fat is a more concentrated energy source, providing more than twice as many calories per gram as carbohydrates. However, the process of converting fat into usable energy is slower and more complex than the conversion of carbohydrates. Thus, it plays an especially important role in endurance activities that last longer than two hours. That is the period that, for an average athlete, marks a carb-stored exhaustion point, hence runners experience rapid deterioration when performing at a high intensity.

Interconnection and Dependency

The relationship between carbohydrate and fat metabolism during exercise is often summarized by the phrase, "fats burn in the flame of carbohydrates." This metaphor highlights an important biochemical reality: the metabolism of fat is contingent on the presence of some products derived from carbohydrate metabolism. Specifically, the cycle that burns fat (the Krebs cycle) requires an intermediate product of carbohydrate metabolism (oxaloacetate) to effectively process fat-derived acetyl-CoA into ATP.

During prolonged physical activity, as glycogen stores are depleted, the body increasingly relies on fat as an energy source. However, if carbohydrate availability is extremely low, the fat oxidation rate can decrease because there isn’t enough oxaloacetate. This scenario underlines why completely depleting carbohydrate stores can be detrimental to performance, particularly in endurance sports.

Balanced Fueling Strategy

Athletes are encouraged to utilize both fats and carbs for energy during activity for several reasons. First, using both fuel sources can enhance endurance by sparing glycogen stores for when intense bursts of energy are needed, such as in the final sprint of a race. Second, a mixed fuel approach reduces the likelihood of "hitting the wall," a common phenomenon where athletes experience a dramatic decline in performance and fatigue as glycogen stores are exhausted.

Moreover, training the body to efficiently use fats in addition to carbohydrates can benefit athletes by increasing their metabolic flexibility, which is the ability to switch between fuel sources depending on availability and demand. This is particularly useful in long-duration sports, where energy demands are high and vary.

Any activity that lasts longer than 2 hours depletes glycogen storage in muscles, leaving working muscles with limited resources. Research shows that there is a hierarchy in metabolism burning during prolonged exercise, and fat burning has a higher priority over blood glucose when glycogen stores are depleted. On the other hand, the improved endurance capability observed after aerobic training has been attributed to increased oxidation of fat relative to carbohydrates; this carbohydrate sparing presumably delays the point at which reduced carbohydrate reserves cause fatigue. This effect has led to the suggestion that a greater availability of fat during exercise can improve performance via the carbohydrate-sparing effect of "fat loading."

Advantages of Consuming MCTs During Endurance Activities

Medium-chain triglycerides (MCTs) are a unique type of fatty acid that offer several advantages for endurance athletes. Unlike long-chain fatty acids, MCTs are absorbed quickly and transported directly to the liver, where they are rapidly converted into ketones. This quick conversion provides a fast-acting energy source that can be particularly beneficial during long-duration activities when glycogen stores are dwindling. Additionally, because MCTs are processed in the liver, they are less likely to be stored as body fat than other dietary fats. This makes MCTs an efficient fuel that can help sustain energy levels without the risk of fat accumulation. Athletes often use MCT oil as a supplement during endurance training and events to enhance their energy output and increase their fat oxidation capacity, thereby extending their endurance and delaying fatigue. This ability to provide quick, sustainable energy without significantly impacting glycogen stores makes MCTs an appealing option for athletes looking to optimize their performance in endurance sports. 

The Marketing of Carbohydrates

Many sports nutrition brands focus on selling carbohydrate-rich products, promoting them as the optimal fuel for exercise. This marketing strategy is based on the immediate performance boost that carbohydrates can provide. However, it often overlooks the long-term benefits of a more balanced approach to fueling, which includes fats. By promoting carbohydrates as the sole essential fuel, these brands might not provide athletes with the full picture of what their bodies need for prolonged and varied-intensity exercise.

While carbohydrates are indeed a crucial component of sports nutrition, they are not the sole player. A deeper understanding of how fats and carbohydrates work together to fuel different types of exercise can lead to better nutrition strategies that enhance performance, endurance, and overall health. Athletes should consider a balanced intake of both carbohydrates and fats to fully harness their body’s energy capabilities during extended physical activity.

Glucose might be a preferred energy source for muscle cells, however, an athlete is more just muscle cells. All evidence show that glucose is not a preferred energy source for humans. Instead of trying at any cost to maximize carb per hour rate (while puking and making frequent stops in the bushes), mix in some fats and see if that works better for your overall performance!

Spring Energy since its inception stood behind the idea of creating performance nutrition products made with unprocessed ingredients that provide numerous sources of energy. 

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Wolfe RR. Adv Exp Med Biol 1998;441:147-56.