Are Carbohydrates Important for Fitness and Performance?
Carbohydrates often get a bad reputation, with some labeling them as nonessential because the body can technically survive without them. The human body can biosynthesize all the glucose it needs for survival by drawing on noncarbohydrate tissues and their metabolites. However, while they may not be essential for mere survival, carbohydrates play a critical role in optimizing athletic performance and muscle growth.
Why Carbohydrates Matter
Carbohydrates are one of the three macronutrients, providing 4 kcal per gram. Their primary function is to serve as an energy source and support glucose and insulin action, cholesterol and triglyceride metabolism, and fermentation. Carbohydrates contain sugars such as glucose and fructose and are our body's main source of energy. In fact, glucose is so crucial that our bodies will convert protein into glycogen via gluconeogenesis when carbohydrate intake is insufficient. This makes carbohydrates protein-sparing, highlighting their importance in a balanced diet.
Glycogen, the stored form of carbohydrates, varies based on lean body mass, diet composition, and training demands. Adults typically store around 350 to 700 grams of glycogen in skeletal muscles and 100 grams in the liver.
Despite fat having nearly double the energy content of carbohydrates, fat oxidation is an inefficient way to produce ATP (the body's energy currency). Glucose oxidation is two to five times faster, making carbohydrate availability crucial for exercise intensities greater than ~60% of maximal oxygen consumption.
Carbohydrates and Athletic Performance
Among all macronutrients, carbohydrates are most closely linked to both total daily energy demands and the energy needs of specific training sessions or competitions.
When you consume carbohydrates, your body goes through a process of digestion, absorption, and transportation. This means that as carbohydrates are broken down, their molecules must be delivered to various tissues to be used as energy.
Skeletal muscle plays a key role in this process, serving as the primary site for glucose uptake and utilization. This makes carbohydrates essential for fueling athletic performance and sustaining high-intensity efforts.
Carbohydrate Recommendations for Athletes
According to the International Society of Sports Nutrition, carbohydrate requirements depend on activity level:
General fitness (no performance goals): 3-5 g/kg per day
Moderate training (~1 hour/day): 5-7 g/kg per day
High training (1-3 hours/day): 6-10 g/kg per day
Very high training (4+ hours/day): 8-12 g/kg per day
Carbohydrates and Muscle Gain
Resistance training, also known as strength training, is widely recognized as the most effective way to maximize muscle growth. Carbohydrates play a crucial role in this process by providing the energy needed to support progressive resistance training.
They serve as the primary fuel source for high-intensity muscle contractions, whether sourced from within the body (endogenous sources such as glycogen and circulating glucose) or from the diet (exogenous sources like carbohydrate-rich foods and beverages).
To optimize muscle growth, carbohydrate intake should align with the demands of strength performance. Research suggests that consuming between 3 to 8 grams of carbohydrates per kilogram of body weight per day is an effective range for maximizing muscle growth.
Carbohydrates and Fat Loss
Fat loss ultimately boils down to maintaining a caloric deficit over time, regardless of carbohydrate intake. There is no magic carbohydrate threshold for optimizing fat loss, and various diets (such as keto or high-carb/low-fat) can be effective as long as adherence is maintained.
While ketogenic diets are popular for their rapid initial weight loss due to glycogen depletion and water loss, they are often challenging to sustain. Research consistently shows no fat loss advantage when protein and total calories are equated between ketogenic and non-ketogenic diets.
Timing Carbohydrate Intake for Performance
Pre-Exercise
Maximizing glycogen stores before exercise is crucial for endurance performance. In the two days leading up to an event, increasing carbohydrates by 10-20% can help optimize stores. On the day of the event, consuming 60-100 grams of carbohydrates 2-4 hours before exercise enhances performance and delays fatigue.
Carb Loading: Does It Work?
Carb loading might work for some, but it’s not the best way to fuel for an event. Here’s what really happens with carb loading through big meals.
If you eat a large meal the night before a race, your body won’t fully absorb it until midday the next day at the earliest. When you consume too much food at once, your small intestine activates a mechanism called the “ileal brake.” Think of it as your body’s “food traffic control” system. This brake kicks in when the last part of your small intestine (the ileum) detects an overload of undigested fats.
Normally, a small amount of undigested food reaching this area is fine, but too much signals the body to slow or even stop digestion until everything is properly processed. This slowdown helps optimize nutrient absorption, decreases appetite, and regulates digestion—but it can work against you before an event.
Imagine having a huge meal the night before your race. Around 4-6 hours into digestion—possibly in the middle of the night—your body triggers the ileal brake. This means your digestive system is still hard at work when it should be recovering. Blood that could have been used for muscle repair is instead directed to your intestines to digest the heavy meal. As a result, your sleep quality may suffer, and you could wake up dehydrated.
If your meal was high in salt, your body will respond by increasing salt excretion in your sweat and urine to restore balance—something that can hurt your hydration status during the race.
By the time you wake up, you’ll likely eliminate yesterday’s breakfast and lunch, but that big dinner is still sitting in your system. Now, you’re adding a pre-race breakfast and fluids into an already slowed digestive process.
Your stomach and small intestine may struggle to process them efficiently. Worse, the fluids needed to digest your heavy dinner—along with the excess sodium—could leave you more dehydrated than usual. This means starting your race with lower sodium levels, poor hydration, and a stomach that’s still working overtime.
Once you hit the course, things can get uncomfortable. With every stride, your partially digested food sloshes around in your intestines, leading to fermentation, gas, bloating, and nausea. Meanwhile, the fluids you consume during the race won’t absorb as effectively, and your body, prioritizing your working muscles, further slows digestion. If your body is still excreting excess salt, you could find yourself in an even worse hydration state.
Things can get really messy—trust me, I’ve heard the horror stories.
During Exercise
For endurance events lasting over two hours, consuming carbohydrates steadily can sustain performance. A general recommendation is 30 grams of carbohydrates every 30 minutes.
Personal Strategy: One effective option is banana rice balls made by mixing a cup of cooked rice with 1-2 mashed bananas and forming them into easy-to-eat portions wrapped in foil. Electrolytes, such as Pedialyte powder, can also help maintain hydration and energy levels.
Post-Exercise
Strategic and timely carbohydrate consumption after exercise is crucial when rapid glycogen replenishment is needed, particularly in endurance sports with short recovery periods. To maximize glycogen resynthesis, research suggests consuming carbohydrates at a rate of 1.2 grams per kilogram of body weight per hour for four to six hours post-exercise.
The type of carbohydrate consumed can significantly impact the speed of glycogen replenishment. The glycemic index (GI) of a food reflects its ability to raise blood glucose levels, which directly affects how efficiently glycogen stores are restored. In situations where quick recovery is essential, high-GI carbohydrate sources are recommended to accelerate glycogen resynthesis.
Glucose, with its high GI, is the preferred choice for post-exercise recovery, whereas fructose, which has a lower GI, is less effective on its own. Studies comparing the two have shown that glucose and glucose polymers provide superior glycogen replenishment compared to fructose, whether consumed alone or as part of a mixed meal.
The Importance of Fiber
Dietary fiber is classified as a complex carbohydrate and consists of a variety of plant-based compounds that are not fully digested in the human gut.
These include a diverse range of non-starch polysaccharides such as beta-glucan, cellulose, hemicellulose, gums, lignin, pectin, mucilage, and resistant starch.
Research consistently supports a minimum fiber intake of 25 to 29 grams per day to reduce the risk of all-cause and cardiovascular-related mortality, as well as the incidence of conditions such as coronary heart disease, stroke, type 2 diabetes (T2D), and colorectal cancer.
These recommendations align with dietary guidelines suggesting an intake of 14 grams of fiber per 1,000 kilocalories for both children and adults.
Although fiber is often thought of as calorie-free, it provides an average of approximately 2 kcal per gram. Interestingly, higher fiber intake has been associated with greater weight loss and improved dietary adherence, independent of overall macronutrient and calorie intake.
While fiber technically contributes to caloric intake, it may support weight loss through mechanisms such as increased satiety, leading to lower overall energy consumption, and a higher thermic effect from digesting fiber-rich foods.
Debunking the Myth: Will Carbs Make Me Fat?
One of the biggest myths in the fitness industry is that carbohydrates make you fat. In reality, carbohydrates cause water retention, not fat gain. After a day of eating a lot of carbs, the number on the scale may go up, and after a few days of cutting carbs, you might see it drop (as mentioned earlier in the carbs for fat loss section). However, these fluctuations don’t reflect actual fat loss or gain.
For every gram of carbohydrates you consume, your body retains about four grams of water to process it. This means your scale weight can fluctuate based on your carb intake. Since the human body is composed of 50-60% water, it's normal for up to 10% of your body weight to come from water fluctuations.
So, if you notice the scale going up after indulging in carbs, remember—it’s just water, not fat gain.
Key Takeaways
Carbohydrates are critical for athletic performance, muscle growth, and energy production.
Timing and intake should be tailored to training demands and personal goals.
Fat loss can occur with any carbohydrate intake level, provided a caloric deficit is maintained.
Myths about carbohydrates causing fat gain stem from water retention rather than actual fat accumulation.
By understanding the vital role of carbohydrates, you can optimize your nutrition to fuel performance, support recovery, and achieve your fitness goals effectively.
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