為什麼我們不該避開碳水化合物

Have you ever wondered how some people are able to perform so well hour after hour, day after day? Is it genetics, lifestyle, or some type of superhuman power?  

Many factors affect a person’s ability to perform on any given day.  Training regimens, recovery techniques, biology, and more. But one of the more important factors is nutrition.

Nutrition is a broad term, consisting of various macronutrients (carbs, fats, and protein), micronutrients (vitamins and minerals), and phytonutrients (lycopene, anthocyanins, etc.). All nutrients have an important role in the human body, but some are utilised more during activity than others. 

So, which of these nutrients play a vital role in activity and performance?

You may be thinking of Vitamin D, or maybe those B12 shots everyone seems to be getting. But it comes down to something much simpler. Something that has been a part of the average person’s diet for centuries.

Carbohydrates

Carbs are not only important during activity but are necessary for cellular energy, peak performance, and optimal recovery. 

Low-carb foods and low-carb dieting techniques, like Keto, have been around for years and seem to go in and out of style. And while low-carb diets have their place, active individuals should think twice before jumping into one of these rather restrictive eating patterns. 

Not only are carbohydrates the brain’s favourite energy source, but they also play a vital role in normal bodily processes like hormone regulation and sleep.¹  

Over the last half-century, a large amount of research has been conducted, showing that consuming carbs can improve athletic performance. Studies have looked at everything from performance effects on endurance and resistance training, to effects on recovery and training adaptations. 

Let’s break down what the research has to say about this underestimated and often underutilised macronutrient.

This is Your Brain on Carbs

To fully understand the ways carbs work in the body, it’s important to understand glucose.

Glucose is a simple carb that is an important energy source used in your body. Nearly all of the carbohydrates you consume will eventually be broken down into glucose so it can fuel your body’s trillions of cells.

Your brain alone is made up of billions of neurons that each require glucose. The brain does not have a store for glucose like muscles do, so it requires a continual supply. Fun fact: This makes the brain the most energy-using organ in the human body, consuming ~120 g of glucose, or nearly 2,090 kJ / 500 calories per day!³ 

When glucose isn’t sufficiently flowing through the body, proteins and fats can be used in place of glucose, but only under different physiological conditions using alternative metabolic pathways (i.e. ketosis). However, these fuels cannot fully replace the functions fulfilled by glucose. 

Cognitive Function

So if there are no glucose stores in the brain, can it run too low on glucose? 

It absolutely can, and it can happen quicker than you might think. 

Low levels of glucose in the brain can negatively affect hormone levels which can lead to cognitive dysfunction — difficulty speaking, thinking, and blurred vision, confusion and delirium. Extremely low glucose levels can even result in cognitive failure, stupor, seizures, and in some very serious cases coma and death.

Hunger

Carbohydrates can also benefit the brain through their effect on the hormone Leptin. 

What exactly is Leptin?

Leptin is a hormone that plays a major role in the regulation of satiety. It’s also the antagonist to the hunger hormone Ghrelin. So if your Leptin levels are low, the hunger hormone Ghrelin is most likely high — Allowing hunger to take over!

Carbohydrates play a larger role in Leptin levels than any other macronutrient. But it’s essential to consume adequate amounts of all three of the macronutrients to keep these hormones in full working balance. 

Avoiding carbohydrates could lead to hunger, limiting the ability to perform mentally and physically.

Carbs and Energy

Energy production allows the body to function normally, enables humans to perform daily tasks, and helps us take on more strenuous workouts and activities. The main and preferred method to produce energy for these tasks is through carbohydrate metabolism, or the breakdown of carbs into glucose (and then ATP) to be used as fuel. 

Muscular Energy

For muscles to produce energy, they must receive oxygen. Red blood cells flow through the body carrying oxygen throughout the body. For RBCs to function they need glucose. Every red blood cell within the body needs glucose to properly allow for the delivery of oxygen from our lungs into our tissues for energy production.¹¹

So next time you take a big breath of fresh air, you can go ahead and thank the oatmeal you had for breakfast for fuelling the delivery of that same oxygen into your muscles!

Specialised Cell Energy

The kidneys renal medulla’s cells rely on glucose for fuel as well. This is extraordinarily important (especially in active individuals) because the kidneys help maintain a healthy fluid and electrolyte balance within the body.¹¹

Without this regulation system being fuelled by glucose, not only would an athlete’s performance suffer, but the body’s entire functionality would be strongly impacted.¹¹

Carbs and Athletic Performance

Carbs and exercise — A duo that has gone hand-in-hand since humans started studying sports nutrition.

Athletic training and exercise require individuals to utilise and burn through a lot of energy. And as we know, the body’s preferred source of energy comes from glucose. This means to be able to consistently provide the glucose your body needs to keep things firing on all cylinders, consistent carbohydrate intake, before and during activity is needed. 

Moderate to high intensity endurance activities and resistance-based workouts rely extensively upon carbohydrates as a fuel source; consequently, another “g” word comes into play — glycogen.

Glycogen is the storage form of glucose within the body’s liver and muscles. These glycogen stores are limited and operate as a predominant source of fuel for up to a few hours during moderate to high-intensity exercise. 

As glycogen levels decline, the ability for an athlete to maintain intensity and work output also decreases while the rate of tissue breakdown increases. Essentially your body starts tapping into your muscles and other tissues to create more fuel, a process that is not very efficient or ideal.

To maximise your energy levels before workouts, consuming adequate carbohydrates to top off your glycogen stores will allow your body to fuel efficiently.   

Carbohydrate Intake Prior to Training

It is recommended that athletes consume high-carbohydrate snacks and meals (1–4 g/kg/day) for several hours before higher-intensity, longer duration (> 90 min) exercise.¹⁰ If an athlete has been relatively low on carbohydrate intake for days prior to a competition, they have an even larger need for high-carbohydrate snacks on competition day. This is especially true for those who have not had appropriate amounts of rest and recovery between sessions. 

A research study found that a daily carbohydrate intake of 9–10 g/kg/day (that’s over 600 grams of carbohydrate for a 68 kg / 150-pound individual in six trained men participating in soccer, rugby, hockey, or basketball, sufficiently replenished muscle glycogen following consecutive days of prolonged (85–90 min), intense, interval exercise.¹⁰

Carbohydrate Intake Prior to Training 

It is recommended that athletes consume high-carbohydrate snacks and meals (1-4 g/kg/day) for several hours before higher-intensity, longer durations (>90 min) exercise.10

Carbohydrate Intake During Training

Carbohydrate consumption during exercise has been shown to help conserve protein, reduce the catabolism of Lean Body Mass (LBM), and help to restore positive energy balance during intense exercise. Carbohydrate administration throughout intermittent, team-sport activities has been shown to improve performance as well as general indicators of mental drive and acuity. For optimal athletic performance, the research supports the practice of consuming carbohydrates both leading up to and during intense training periods. 

The number of carbs recommended varies for different workout lengths and intensities. During shorter, lighter intensity workouts taking in carbohydrates is a little less crucial. Whereas carb intake during endurance activities of over ~90 minutes becomes extremely important to maintaining power output and overall performance. 

Endurance Training

Research has demonstrated that providing carbohydrates at regular intervals during exercise (every 10–12 min) can optimise performance and maintain blood glucose levels in endurance athletes. When carbohydrates are ingested more frequently during an endurance event or training session, it is possible for performance to be improved.

As we know, muscle glycogen is extremely important during activity, especially in endurance athletes as their demands for energy are quite high. The recommended daily intake of carbohydrates for endurance-type athletes is around 5–12 g/kg/day, with the upper end of this range (8–12 g/kg/day) for those athletes that are training at moderate to high intensities upwards of 12 hours per week. These carbohydrate amounts have been shown to maximise the body’s ability to store glycogen.¹⁰

For Example: 68 kg / 150 lb Male Triathlete aiming for 5-12 g/kg/day of Carbohydrates           

= 340-818 Grams of Carbohydrates per day 

As a reference point, one slice of whole wheat bread typically contains just about 12-15 Grams of Carbs — So this goes to show just how many carbs it takes for an endurance athlete to maximise their glycogen, and performance potential!

It’s important to remember, while these are good general recommendations, every body is different, and everyone’s training is different. Deciding how many carbs to consume during endurance training depends on the intensity and duration of the event or workout, as well as the person.

As we continue to learn more and more about the genetic and physiological differences between the sexes, more research is emerging that fuel utilization during exercise may be one of those differences. Evidence shows that trained female athletes actually do not oxidise fat and carbohydrate at the same rates as males and may deplete glycogen stores differently¹⁰. Female athletes may, in fact, need to increase total caloric intake to achieve glycogen resynthesis effects like males.¹⁰

Resistance Training

Even if you’re not actively training for an endurance event, there’s still a good chance you’re doing some resistance and strength training. If you’re not, you probably should. But, just like endurance training, strength training requires carb intake to maximum power and total weight.  

Consuming adequate carbohydrates prior to training can reduce glycogen depletion and may therefore enhance performance and output in the weight room. Carb ingestion during resistance exercise has also been shown to promote euglycemia (normal blood glucose concentration) and higher glycogen stores, and glycogen within the muscle is directly related to the potential energy output of that same working muscle. 

What does all this mean? Well, think of glycogen like the gas tank of your car.

If you only put 8 gallons of fuel into your empty 16-gallon tank, you’re only able to use 8 gallons. However, if you fill your tank completely, you’re able to go double the number of miles, plus you’ll have a little more in you to crank those RPMs!

Glycogen works roughly the same way. You fill your glycogen stores halfway — You’re likely to perform with less intensity and for much less duration. You fill them completely — You should be able to perform at a much higher intensity and for twice as long.

During high-intensity (>70% VO₂ max) resistance training of 70+ minutes, energy stores and fluid balance become extraordinarily challenged. After 70 minutes of high-intensity work, carbohydrates are recommended to be consumed at a rate of ~30–60 g of carbohydrate over every hour in a carbohydrate-electrolyte solution throughout the entire exercise bout.¹⁰

Sipping on the carbohydrate beverage rather than chugging it is preferred to ensure consistent blood glucose concentrations and glycogen resynthesis rates. This will warrant your ‘engine’ to run to the best of its capacity for the entire training session, giving your body the best opportunity to see results. 

Carbohydrate Intake in Post-Exercise Recovery

Recovery is a crucial part of a proper training regimen. If our recovery is lacking, we simply cannot perform at a high level on a day-to-day basis and increases your risk of injury. 

There are three components to quality post-exercise recovery often referred to as “the three R’s” of post-workout recovery:  Rehydration, regeneration and repair of damaged muscle tissue, and replenishment of depleted glycogen stores. Carbs play a big role in two of the three — Replenishment of glycogen and repair of muscle tissue.

The type and timing of the ingested carbohydrate, the training status of the athlete, and the duration of the post-exercise recovery period are all factors that play a role in dialling in the right amount of carbohydrates needed to optimally recover. 

Replenishment of Glycogen

Post-exercise consumption of carbohydrates is necessary, and in situations where minimal recovery time is available a more aggressive carbohydrate feeding approach is recommended. Consuming protein in addition to carbohydrates during the recovery period has been reported to accelerate the rate of muscle glycogen resynthesis relative to a carbohydrate-only supplement when ingested.²

To maximise the recovery process and muscle glycogen resynthesis, especially when recovery time is short, ingesting multiple sources of carbohydrates is recommended. Taking in different types of carbohydrates after exercise will allow for maximal absorption and maximal glycogen resynthesis, both of which are of high importance for the recovery process. 

Fructose ingestion does not stimulate muscle glycogen resynthesis to the same magnitude as glucose or sucrose. Sucrose and glucose seem to stimulate muscle glycogen resynthesis at a similar level. Interestingly, glucose + fructose, or glucose + sucrose ingestion elicit similar muscle glycogen resynthesis rates as well. 

So in short, fructose does a better job at regenerating liver glycogen while glucose does a better job at regenerating muscle glycogen. Because of this, it’s best to ingest a mixture of glucose and fructose to provide an optimal dose of carbohydrate for the effective restoration of both muscle and liver glycogen stores. Sucrose is made up of glucose and fructose, so it seems justifiable to use this carbohydrate in optimising overall carbohydrate stores. 

Carbs and Sleep

Have you ever noticed that tired sleepy feeling after eating a big Thanksgiving meal? We all have wondered why this happens and where the closest pillow is. 

Tryptophan may be the culprit. 

Tryptophan is an amino acid that increases serotonin levels within the body. Serotonin is what makes melatonin — the hormone that regulates our sleep! And of course, sleep is essential for our bodies to recover and repair from all the strenuous activity we do each and every day. 

While tryptophan is generally associated more with protein, carbohydrate consumption has actually been shown to increase tryptophan levels within our bodies.⁵ Carbohydrates affect tryptophan levels in the blood and may complement the sleep-enhancing effect of consuming tryptophan-rich protein (all that turkey).⁵

How is this possible?  

Well, after the ingestion of carbohydrates and rise in blood sugar, the hormone Insulin is secreted. Insulin influences the transport of tryptophan into the brain after a carbohydrate-rich meal.⁵

Additionally, consuming higher glycemic index carbohydrates (white rice, potatoes, corn, bagels, cereals, etc.) several hours prior to bed has been found to aid in the process of falling asleep. Higher carbohydrate diets have also been associated with increased REM and decreased wakefulness.⁵ On the other hand, lower carbohydrate diets have actually been associated with symptoms of insomnia. 

As you can see, there are numerous benefits to consuming carbohydrates within several hours before bedtime to aid in a much deeper, more beneficial sleep. And let’s face it, sufficient recovery cannot be obtained without adequate sleep.

It seems like we’re always looking for the next new thing to come out and improve an athlete’s ability to succeed and perform, but sometimes it’s best to go back to the basics.

All three macronutrients are essential for optimal health and crucial in helping you reach your athletic and fitness goals. Avoiding a specific macronutrient will only hinder you from reaching your absolute best health. 

If you’re aiming for optimal brain function, athletic performance, exercise/training, post-exercise recovery, and sleep quality, fear carbohydrates no more!

Despite what some companies’ low-carb marketing tactics may try to tell you, carbs are a great source of energy and an integral part of a balanced diet for active and healthy individuals. Consuming carbohydrates prior to, during, and after training will assist you in performing your best and recovering the quickest. You will be blown away at your energy levels after implementing a higher carbohydrate diet relative to your lifestyle. 

Plus, carbs just taste good!

References 

1. Adamska-Patruno, E., Ostrowska, L., Goscik, J., Pietraszewska, B., Kretowski, A., & Gorska, M. (2018). The relationship between the leptin/ghrelin ratio and meals with various macronutrient contents in men with different nutritional status: a randomized crossover study. Nutrition Journal, 17(1). doi: 10.1186/s12937-018-0427-x
2. Alghannam, A., Gonzalez, J., & Betts, J. (2018). Restoration of Muscle Glycogen and Functional Capacity: Role of Post-Exercise Carbohydrate and Protein Co-Ingestion. Nutrients, 10(2), 253. doi: 10.3390/nu10020253
3. Berg JM, Tymoczko JL, Stryer L. Biochemistry. 5th edition. New York: W H Freeman; 2002. Section 30.2, Each Organ Has a Unique Metabolic Profile. Available from: https://www.ncbi.nlm.nih.gov/books/NBK22436/
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5. Doherty, Madigan, Warrington, & Ellis. (2019). Sleep and Nutrition Interactions: Implications for Athletes. Nutrients, 11(4), 822. doi: 10.3390/nu11040822
6. Hearris, M., Hammond, K., Fell, J., & Morton, J. (2018). Regulation of Muscle Glycogen Metabolism during Exercise: Implications for Endurance Performance and Training Adaptations. Nutrients, 10(3), 298. doi: 10.3390/nu10030298
7. Heart Rate Science. Retrieved Jan. 30, 2020, from https://pinkgym.com/heart-rate-science/
8. Helms, E. R., Aragon, A. A., & Fitschen, P. J. (2014). Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. Journal of the International Society of Sports Nutrition, 11(1). doi: 10.1186/1550-2783-11-20
9. Jeukendrup, A. E. (2017). Training the Gut for Athletes. Sports Medicine, 47(S1), 101–110. doi: 10.1007/s40279-017-0690-6
10. Kerksick, C. M., Arent, S., Schoenfeld, B. J., Stout, J. R., Campbell, B., Wilborn, C. D., … Antonio, J. (2017). International society of sports nutrition position stand: nutrient timing. Journal of the International Society of Sports Nutrition, 14(1). doi: 10.1186/s12970-017-0189-4
11. Kokkinidou, S., Peterson, D., Bloch, T., & Bronston, A. (2018). The Important Role of Carbohydrates in the Flavor, Function, and Formulation of Oral Nutritional Supplements. Nutrients, 10(6), 742. doi: 10.3390/nu10060742
12. Vitale, K., & Getzin, A. (2019). Nutrition and Supplement Update for the Endurance Athlete: Review and Recommendations. Nutrients, 11(6), 1289. doi: 10.3390/nu11061289
13. Williams, C., & Rollo, I. (2015). Carbohydrate Nutrition and Team Sport Performance. Sports Medicine, 45(S1), 13–22. doi: 10.1007/s40279-015-0399-3