If you hang out with most athletes, you can tell when they are going to compete based on their diet. The night before the game or meet, it is common to see an athlete eating extra servings of spaghetti, potatoes, rice, bread, bananas, etc. Research from the 1960s suggests that athletes consume extra carbs before competitive events, but did the research tell the entire metabolic story? Did all of this "carb loading" actually benefit athletic performance?
What is Carb Loading?
Mayo Clinic explains:
A carbohydrate-loading diet, also called a "carb-loading diet", is a strategy to increase the amount of fuel stored in your muscles to improve your athletic performance for endurance events.
Carbohydrate loading is a result of continuing to eat a high-carbohydrate "training diet" while scaling back your activity level during carbohydrate loading.
When did carb loading start?
Running Competitor explains:
The practice of carbo-loading dates back to the late 1960s. A Swedish physiologist named Gunvar Ahlborg introduced the first carb-loading protocols after he discovered a positive relationship between the amount of glycogen (carbs stored in the muscles and liver) in the body and endurance performance.
Scientists and runners had already known for some time that eating a high-carbohydrate diet in the days preceding a long race enhances performance, but no one knew exactly why until Ahlborg's team zeroed in on the glycogen connection.
What this the purpose of consuming the carbs?
Any physical activity requires carbohydrates for fuel. For most recreational activity, your body uses its existing energy stores for fuel. But when you engage in long, intense athletic events, your body needs extra energy to keep going. The purpose of carbohydrate loading is to give you the energy to complete an endurance event with less fatigue, improving your athletic performance.
Does the carb-loading research still hold true today?
Stephen Phinney, a doctor and nutritional biochemist worked with Jeff Volek at the University of Connecticut. Phinney started experimenting back in the 1980s to investigate the benefits of carb loading.
We were pretty sure we'd prove that the carb-loading concept was correct.
To Phinney and Volek's surprise, they discovered just the opposite; athletes in their experiments performed their very best on nearly zero carbohydrates. With the absence of glycogen (the form that is stored in the muscles and liver), the body switched its fuel source to molecules derived from fatty acids in the blood called keytones.
Phinney and Volek explain:
Our bodies can be viewed as the physiological equivalent of hybrid automobiles, switching back and forth between fuel sources: when we can't burn energy from carbohydrates, we burn our fat stores instead.
It is instructive to point out that ever since the observation over four decades ago that low muscle glycogen was associated with fatigue, most of that progress has been focused on ways to enhance glycogen levels and carbohydrate oxidation. Little effort has been devoted to developing methods to decrease the body's dependence on carbohydrate during physical activity.
Is the research used to support high carbohydrate diets flawed or in some way misaligned with what we know about human physiology? Not exactly - its more a case of willful neglect. Many of the experiments conducted during that time were designed in a specific manner and data interpreted within a narrow manner to support and confirm the high carbohydrate paradigm.
What do we understand about carbs and performance?
Volek explains further:
Adenosine tri-phosphate (ATP) is the chemical energy that fuels body processes including muscle contraction. Its literally the energy that causes your muscle fibers to contract and produce force. The two primary fuels our bodies draw on to produce ATP are carbohydrate and fat. How does the body chooses the proportion of carbohydrate and fat is used to fuel is complex but one factor that has a consistent and profound effect is the availability of carbohydrate.
The more carbs that are available, the more carbs the body burns; while at the same time shutting down the access to its much larger fuel reserve - fat.
Glucose can be metabolized directly to make ATP and glucose can be also be stored in modest amounts of glycogen in skeletal muscle, and to a lesser extent in liver. Since 1 gram of carbohydrate equals 4kcal, you max out at about. 1600-2000kcal in your carbohydrate fuel tank. If you carry more muscle mass, are well trained , and eat a high carbohydrate diet, your glycogen stores might be increased by another 50% or so but the total amount of carbohydrates available in the body is still relatively low compared to available fat stores.
Fat, or more specially fatty acids, are stored in the body as triglycerides. Unlike our limited storage of glycogen, fat cells have vast capacity to store fat. Since fat contains 9kcal per gram and is stored with minimal water, they are an efficient storage form of low energy that can be mobilized quickly when blood insulin levels are low. Even in a very lean athlete, the total amount of energy stored as fat will typically be more than 20times the maximum level of carbohydrate stored in the body.
For instance, if an athlete has 20lbs of fat on them and 1 lbs of fat has 3,500kcal, then the athlete will have 70,000kcal available at all times. While the body can burn both glucose and fat, it has "unlimited" calories from the fat stores. As a result, the body is most efficient when it burns fat.
Besides exacerbating insulin resistance, a high carbohydrate diet also locks a person into a dependence on carbohydrate as the dominant fuel for exercise.
Once your carbs (glucose) is gone from the blood stream, you can't power your performance with fat (even though a carbohydrate-depleted body still has tens of thousands of fat calories on hand).
Since humans have a limited capacity to store carbohydrate, this requires that endurance athletes frequently consume carbohydrates to support their high rates of carbohydrate oxidation during prolonged exercise. This poses obvious logistically problems, both in having timely access to carbohydrate foods/supplements and in maintaining adequate digestive function to allow their absorption without undue gastro-intestinal side effects.
How does this relate to insulin and blood sugar?
Fat breakdown is principally controlled by a single hormone, insulin. In other words, insulin is the primary gate-keeper of body fat. If your insulin levels are consistently high, fat usage is effectively blocked. The primary nutrient that stimulates insulin is dietary carbohydrates.
Like many things in life, a little bit of insulin is necessary but more isn't better. Insulins effects are not limited to promoting glucose uptake and suppressing fat breakdown. In addition to promoting storage of fat insulin also potently and rapidly inhibits blood fatty acid and total body lipid oxidation as well.
This suppression of fat oxidation lasts for days after carbohydrates are consumed, not just the few hours following their digestion when insulin levels are high.
What does this mean?
If an athlete follows the concept of carb loading, they will consume extra carbs (rice, potatoes, etc) a few days before an athletic event until the event takes place. The idea for carb-loading is to get extra glucose in the body. An adult has the maximal storage. capacity to store 1600-2000kcal of glucose,. In comparison each pound of fat has 3,500kcal of energy in it. The maximal capacity is virtually infinite since the body has an unlimited storage of fat. When the athlete begins consuming the carbs, they will elevate their insulin levels. Since all muscle contractions use ATP, the body can use carbs or fat as its fuel source. A chain reaction begins to occur when insulin is released. The insulin stops the body from burning fat as a fuel source and begin using carbs as the primary fuel source. Since the insulin controls fat utilization, it will be days until the athlete can use fat as a fuel source. If the athlete carb-loaded 3 continuous days before the event, it will be days after the event before the athlete will utilize fat as a fuel source. In fact by consuming the carbs, the athlete has actually increase their will body fat. % by storing more fat. (Refer to The Importance of Understanding Insulin). The athletic performance will be significantly compromised and far from optimal. The athlete will be dependent on consuming carbs throughout the event to maintain energy. If the athlete had been consuming a low carb diet all along, their body will have become efficient at utilizing fat as a fuel source because their insulin levels are low. When the athlete performs in the event, they will be able to perform at an optimal level because their primary fuel source is fat, which is an unlimited supply.
Unfortunately, the only way your body stores extra glucose in the body is to have more muscle mass, not by consuming carbs.
What are you to do?
Stop carb-loading. Instead, do the opposite, limit your carbs, not just prior to your athletic event but all the time. Teach your body how to burn fat. When you use fat as your fuel source, your performance will be closer to optimal vs. consuming carbs and comprising your performance. Burn the fat! Perform your best!
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