Carbo-Loading: Fact or Fiction?
March 18, 2021
The practice of gobbling down pasta the night before game-day has long been popular among athletes. But could so-called carbo-loading do more damage than good?
In the early days of the Tour de France (think the 1910s), riders would reportedly chow down on a carb-heavy diet of pastries, pasta, and bread. An updated version of the tradition of so-called “carbo-loading” continues to this day, with riders eating a healthy diet with a higher portion (around 70 percent or 1,100 grams a day for a 150-pound rider) of quality, carbohydrate-rich foods like muesli, rice cakes, and energy bars.
Carb-loading or carbo-loading is a technique that involves packing your diet full of carbs in an effort to maximize your body’s glycogen stores. The strategy has long been utilized by athletes before a big game, race, or competition—but does carbo-loading actually work?
The answer is more complex than you might think. In this post, we get to the bottom of carbo-loading by exploring its history, potential benefits, and risks.
Carbo-loading: A brief history
Athletes have been preparing for competitions with high-carb diets since ancient times when Greek and Roman athletes would consume complex carbohydrates in the form of grains, legumes, and vegetables to optimize performance.
However, the carbo-loading technique wasn’t formally developed until the late 1960s. That’s when Swedish physiologist Gunvar Ahlborg first published a report revealing the positive relationship between the amount of glycogen, or carbs stored in the muscle and liver, and athletic performance in endurance sports. Ahlborg also found that the body was able to store higher amounts of glycogen when a high level of carb consumption was preceded by a low level of carb consumption.
Based on his findings, Ahlborg developed a seven-day carbo-loading plan that included intense training followed by three or four days of extremely low carb intake and then three or four days of extremely high carb intake. Trained athletes who followed his method were found to have greater endurance in exercise lasting longer than 90 minutes. However, the method came with problems. Notably, athletes were suffering significant consequences during the period of extremely low carb intake, including fatigue, cravings, and susceptibility to disease.
Since Ahlborg’s report, however, the strategy of carbo-loading has evolved and improved. Subsequent research has indicated that you can increase glycogen storage without dramatically depleting it. Newer carbo-loading plans have athletes eat a normal diet throughout training but switch to a high-carb diet 3-7 days before a competition.
Does carbo-loading actually work?
So, does the theory of carbo-loading hold up in the real world? The answer is yes—but only for a very select type of sports. To understand how carbo-loading works, let’s take a quick look at the science:
Carbohydrates—or the sugar, starches, and fibers found in food—are your body’s primary energy source. During digestion, your body breaks carbohydrates down into sugar. Then, it stores this sugar in your muscles and liver as glycogen, its most easily-accessed form of energy.
When you run out of glycogen, your body hits a “wall” as it works harder to turn fat—its secondary fuel source—into energy. Because you’re suddenly missing your primary fuel source, your body will tell your muscles to slow down. To delay fatigue and avoid hitting a wall, it makes sense to maximize your glycogen stores to keep your body from resorting to burning fat.
Note that it usually takes your body around 90 to 120 minutes to run out of glycogen. That’s why carb-loading is only effective for athletic events that last over 90 minutes, and it’s inadvisable—and potentially even harmful—for shorter activities.
Who should (and should not) carbo-load?
Because most of us easily have an hour’s worth of glycogen in our muscles, only a very small group of athletes should consider carb-loading. Namely, only marathoners, triathletes, and other athletes who perform endurance sports nonstop at a moderate- to high-intensity level for 90 minutes or longer should be concerned about their glycogen stores.
That means the vast majority of us should steer clear of carbo-loading. There is no need to carb-load before a casual or high-intensity workout, a 5K race, or a short bike ride.
Even professional athletes are unlikely to benefit from true carbo-loading. Consider how a game of basketball lasts around 48 minutes, placing it well below the 90-minute threshold. Similarly, in sports like baseball and football, games may run over a couple of hours, but players spend a lot of time sitting and standing around.
Finally, carb-loading isn’t necessary if you can eat during the competition. You can replenish your body’s depleted glycogen stores if you eat carbs while competing. That’s why marathoners may eat gel packets while running, and “Ultramarathon Man” Dean Karnazes notoriously ordered a large pizza at mile 65 of a 199-mile run.
The risks of carbo-loading
For most athletes, carbo-loading is not only unnecessary but also carries serious risks. Below, we’ve outlined a few of the problems associated with carbo-loading.
Digestive issues. Overloading your body with more carbs than it is used to can cause digestive issues like bloating. Similarly, while healthy in moderation, the fiber found in many carb-rich foods can cause constipation and diarrhea when consumed in excess.
Added stress on your body. If you are used to eating a lower or normal amount of carbs, the dramatic shift to carb-loading can stress out your body. As your body and gut struggle to adjust to the drastic change, you may experience headaches, irritability, fatigue, and hunger.
Blood sugar spiking. Consuming excessive amounts of refined carbs can be particularly problematic. Refined carbs—or the sugar and refined grains found in foods like white bread, pizza, white rice, and many breakfast cereals—digest quickly, causing unhealthy spikes in your blood sugar levels. The swing in your blood sugar and insulin levels can lead to hunger, cravings, fatigue, and other problems.
Water retention. If the activity’s length and intensity don’t require stored fuel, carbo-loading can actually slow you down. Carbohydrate intake causes water retention: for every one gram of carbohydrates stored as glycogen, your body retains at least three grams of water. Acting like a ballast, the extra water weight can slow you down and hinder physical performance.
Obesity. Over the long term, excessive consumption of refined carbs has been linked to weight gain, diabetes, and heart disease. Research has found that overweight and obesity risk is lowest among people who get 47 to 64 percent of their calories from carbohydrates.
How to carbo-load the right way
Even if you are preparing for a multi-hour endurance event, you may run into problems if you carbo-load improperly. Surprise, surprise: The common practice of gobbling down a bunch of Italian food the night before your race isn’t likely to do you much good. In fact, Norwegian distance runner Grete Waltz, who won eight NYC marathons, said she avoided eating a big meal the night before a race to avoid tummy troubles the next day.
Because you can’t completely fill your glycogen stores with just one massive meal, it’s recommended to start carb-loading over the course of 3-6 days before your endurance event rather than relying on a single pasta dinner the night before. Equally important to timing is eating the right type of carbs when you carbo-load. While following a carbo-loading diet, stick to low-glycemic foods like sweet potatoes, oatmeal, whole-wheat pasta, grains like quinoa and couscous, and legumes. At the same time, avoid refined carbs like white bread, white rice, pastries, and sweets. “A common mistake is to load purely with starchy wholefoods and roughage to which your body may not be well adjusted, which can cause stomach upset,” says cyclist, runner, and sport science lecturer Dr. Nick Tiller. “To avoid this, be sure to get a mixture of carbs from a variety of sources.”
While everyone’s needs may be different depending on their metabolism, it’s generally recommended that around 70 percent of your calories should come from carbs—as opposed to your usual 50 percent—when carbo-loading.
It’s worth noting that two people with the same weight, height, and training schedule can have drastically different caloric (energy) needs. In addition to the amount of training you do each day, your caloric needs are influence by things like age, gender, body fat and muscle composition, and even climate.
For an accurate estimation of your unique caloric needs, you need to first determine your resting metabolic rate (RMR), or the amount of energy you burn in one day. Knowing the number of calories you burn when totally at rest combined with calories you burn through daily training will you give a precise picture of the total calories you need to eat each day—and what percentage of those calories should come from carbs.
As a rule of thumb, you should be shooting for around 2.3 to 5.5. grams of carbs per pound of body weight per day when carbo-loading. For a 150-pound person, this would be around 600 grams of carbs per day.
How does carbo-loading impact body composition?
A short period of properly performed carbo-loading is unlikely to have a significant impact on your body composition. You may find that you have a higher BMI when carbo-loading, but the excess weight is likely a result of water retention. Water retention may also make your muscles appear larger (which is why some bodybuilders like to carbo-load before competitions), but the mass and tone gained from carbo-loading will be lost as your body circulates fluids.
But while gains in weight and muscle tone are likely to be temporary, prolonged periods of getting 70+ percent of your calories from carbs can lead to more lasting changes. Excessive carb consumption can result in your cells getting more glucose than they need, which your body will convert into fat. Eating too many carbs—especially processed carbs—has been linked to obesity.
If your goal is to lose body fat, gain muscle, or maintain a healthy body composition—and not to optimize performance in endurance sports or bodybuilding competitions—you should focus on getting sufficient protein and fiber rather than spiking your carbohydrate intake.
Build a data-driven fitness and nutrition plan
To develop your ideal nutrition and training strategy, consider getting a body composition scan. Dual Energy X-Ray Absorptiometry (DEXA/DXA) scanning delivers a detailed analysis of the composition of fat, muscle, bone, tissue, and water mass in your body so you can determine whether to focus on fat loss, muscle gain, or maintenance. Schedule a DEXA scan at a Fitnecity partner location near you.
Another, powerful way to unlock the data you need to develop an ultra-individualized and accurate health and nutrition plan? For a precise picture of how many grams of carbohydrates to eat while carbo-loading, consider getting your resting metabolic rate (RMR) tested. Your resting metabolic rate is the minimum number of calories your body needs to perform basic, life-sustaining functions. By adding your unique RMR to the number of calories burned through training, you can calculate the number of calories and carbs you need to consume each day to optimize the carbo-loading process. Schedule an RMR test at a Fitnecity partner location near you.
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