Carbohydrate and Glycemic Index – Exercise Performance

Published by Surajit jana on

Carbohydrate is the important fuel for every type of physical activity that we do in our day to day life and the glycogen stored in  our muscle and liver determine how efficiently we can perform any physical activities.

For athletic performance, the more glycogen stored in our body the more body will allow us to train at higher intensity for a longer time period and achieve greater training effect. 

The less the Glycogen stores in  our body the less our body will permit us to train at higher intensity for a longer time period and body will achieve fatigue earlier resulting in lower athletic performance .

So, it is clear that glycogen stores play the most valuable part in performing any type of physical activities.

This article will give you a detailed explanation about the link between carbohydrate availability,Glycemic index  and exercise performance .

Different carbohydrate foods have different types of effects in our body so here you will get the detailed information. It also has brief information on the Glycemic Index, which is the important part of your nutrition .

Carbohydrate and glycemic index

Relation Between Muscle Glycogen and Exercise Performance

In 1939 it was demonstrated that a high carbohydrate diet significantly increases endurance . This demonstration was given by Christensen and Haren, the importance of carbohydrates in relation to exercise performance . 

In 1960, scientists discovered that the capacity of endurance exercise was related to pre-exercise glycogen stores and the high carbs diet increases the glycogen store .

In one study, there were three groups of athletes given a high carbohydrate diet, moderate carbohydrate diet and low carbohydrate diet . 

The researchers measured the concentration of glycogen stored in their legs. They found the athletes with a high carbohydrate diet stored twice the amount  of glycogen than those with moderate carbohydrate diets and seven times more than those with  low carbohydrate diets .

After the measurement of glycogen stores taken from different groups of athletes they were given a stationary bicycle and are ordered to cycle to exhaust . 

Those with a high carbohydrate diet managed to cycle for 170 minutes and moderate diet athletes cycled for 115 minutes and low carbohydrate athletes cycled for 60 minutes. 

Carbohydrate you need per day

For most of the athletes the recommendation for consuming the carbohydrate diet is high to replenish muscle glycogen level and able to train at high intensity .

It is found in many studies that a high carbohydrate diet will help athletes to enhance their sports performance.

Carbohydrate and Glycemic Index - Exercise Performance

The fact that carbohydrate availability is the limiting factor for endurance training and sports performance as the carbohydrate stored in our body in the form of muscle and liver glycogen are limited .

Depletion of glycogen stores will result in fatigue and reducing training intensity .

This is usually caused when your pre-workout glycogen stores are low . In order to avoid this glycogen depletion you should consume a high carbohydrate diet and ensure that the daily carbohydrate intake matches your daily fuel need for workout and also your pre-workout glycogen stores are high enough .

This technique will help you to increase endurance, delay fatigue and train with higher intensity for longer .

Table below indicate daily carbohydrate intake according to body weight to meet daily fuel requirement :-

Training IntensityDaily Carbohydrate Intake
Low Intensity3 – 5 gm/kg daily
Moderate Intensity 5 – 7 gm/kg daily
Moderately high Intensity 6 – 10 gm/kg daily
High intensity 8 – 12 gm/kg daily

For example –

If your body weight is 85 kg and you are training with moderate intensity you should consume – 85 x 7 gm = 595 gm of carbohydrate daily .

Can we train with a low Carbohydrate diet ?

It is generally accepted that the high endurance workout will require a high carbohydrate diet to replenish the glycogen store but on the other hand numerous scientific studies have found low carbohydrate diet can also be used for workout and has many other benefits to train at low carbohydrate .

The strategy behind the theory of training with low carbohydrates is that fat is used as a major fuel during long endurance workouts when there is no carbohydrate intake and glycogen levels are low .

Carbohydrate and Glycemic Index - Exercise Performance

In other words, by applying this theory practically will help muscle to burn more fat as it will be used as major fuel and conserving the muscle glycogen . 

Since fat is stored in our body for use in energy crisis time , there is plenty of stored fats in our body . 

Applying low carbohydrate diet training from time to time will adapt muscle to increase workout performance and endurance .

Benefits of Low Carbohydrate Diet

There are some benefits of training with a low carbohydrate diet and further studies are ongoing in this topic .

  1. Enhance metabolic adaptation in muscles .
  2. Increase the level of certain enzymes related to mitochondrial biogenesis
  3.  Increase fat oxidation in muscle .
  4. Increase in mitochondria level .

Thus, Training with low carbohydrate diet training adaptation increases and fat burning capacity of muscle increases with the ability to use fat as the main energy source during workout .

So, does training with a low carbohydrate diet improve workout performance ?

Well, till now with aspects to all the scientific study done on this particular topic it is found that despite increasing muscle ability to use fat as energy and burn more muscle fat there is no clear evidence to improve training capacity , performance or glycogen store .

Carbohydrate and Glycemic Index - Exercise Performance

 Drawbacks of Low Carbohydrate Diet

The major drawback of training with a low carbohydrate diet is that it reduces workout capacity for high intensity training and also builds up muscle fatigue quickly  so the muscle power and muscle contraction speed decreases . 

Individuals with low carbohydrate diet trends to choose low weight and low intensity training as the workout feels harder to complete after sometimes .

Another drawback of low carbohydrate training is illness, injury and overtraining muscle stress and also muscle fatigue at rest .

The workout intensity reduction can be overcomed by consuming 1 to 2 mg/kg of body weight during or before workout period .

People on a low carbohydrate diet can also practice rinsing their mouth with carbohydrate drinks during workout .This technique will help to maintain training intensity and avoid muscle protein breakdown . 

Rinsing your mouth with carbohydrate drinks acts on our central nervous system and tells our brain that carbohydrates are on their way . 

This will help reduce fatigue and exertion and help to train for a longer period .

It will be much more beneficial if people swallow the carbohydrate drink instead of spitting it out . In this way the body will get some extra calories and it will be good to go for maintaining workout intensity .

Type of Carbohydrate 

Usually, carbohydrates are differentiated based on their chemical structures . Scientifically carbohydrates are divided into two categories Simple carbohydrates and Complex carbohydrates .

Simple Carbohydrate – Simple carbohydrates are very small molecules consisting of one or two sugar units. 

They are monosaccharides meaning one sugar molecule such as glucose, fructose, galactose and dysaccharates meaning two sugar molecules such as sucrose (table sugar) lactose (milk sugar) .

Complex Carbohydrates – Complex Carbohydrates are larger molecules consisting of hundreds and thousands of sugar molecules which are mostly glucose joined together .

They include starches, amylose, and non-starch polysaccharides which are dietary fiber such as cellulose .

In between Simple and Complex Carbohydrates are glucose, polymers and maltodextrin, which contain 3 to 10 sugar unit.They are made from breakdown of starch in food processing . 

They are usually used as bulking and thickening of processed food . They are also used in sports drinks and meal-replacement supplements for their property of low sweetness and high energy density .

Many food products contain both simple and complex carbohydrates, thus making it difficult to classify the product into simple and complex carbohydrates sources .

Is sugar consumption really harmful for health?

Carbohydrate and Glycemic Index - Exercise Performance

Sugar is a carbohydrate, and it is an energy source for our body . Despite all the negative thoughts out there about sugar, small amounts of sugar are unlikely to cause harm and, provided you time your sugar intake around exercise, it may enhance exercise performance.

 During high intensity exercise for prolonged periods, consuming sugar either in the form of solid food or drinks can help maintain blood glucose concentration, replenish glycogen and increase endurance. 

Sugar may also be beneficial for promoting rapid glycogen refuelling after prolonged intense exercise. 

However, one of the main problems with sugar is its ability to cause dental caries. Studies have shown, who consume lots of sports  drinks and energy bars experience significant tooth decay and erosion .

These products are high in sugar and as they are usually consumed at frequent intervals during exercise, they are particularly damaging to the teeth. Another problem with sugar is that it has no real nutritional value apart from providing energy . 

Carbohydrate and Glycemic Index - Exercise Performance

It makes food and drink more palatable and therefore easy to over-consume. Although sugar is not uniquely fattening, it can contribute towards an overconsumption of calories, especially when combined with lots of fat in the form of cakes, chocolates, biscuits and snacks. 

Although high intakes of sugar is linked with obesity and type 2 diabetes, the main contributor to these diseases is excess calories rather than sugar itself. 

High sugar intakes can result in insulin resistance, where the body cells become less responsive to insulin and the body starts to store fat. 

However, regular exercise reduces the negative effects of sugar, which means the body produces less insulin after consuming sugar. This means our body needs less insulin to do the workout activities and the body adopts to to handle sugar efficiently . 

Most of the negative side effects of sugar is due to the fructose , which increases blood triglycerides level which in turn increases cardiovascular diseases .

If you do regular exercise these risks can be prevented easily as our body will produce lipoprotein lipase, the specific enzyme that removes fat from blood and produces energy .

All Carbohydrates are not equal

We think simple carbohydrates, due to their smaller molecular size, are absorbed more quickly than complex carbohydrates, and increase the blood sugar level quickly . But it is not always correct.

 For example, apples containing simple carbohydrates produce a small and prolonged rise in blood sugar, despite being high in simple carbohydrates. Many starchy foods containing complex carbohydrates, such as potatoes and bread, are digested and absorbed very quickly and give a rapid rise in blood sugar. 

So the old theory about simple carbohydrates and complex carbohydrates absorption is incorrect and misleading. 

What makes food to have different GI values ?

Factors that influence the GI of food include the size of the food particle, the biochemical makeup of the carbohydrate (the ratio of amylose to amylopectin), the degree of cooking (which affects starch gelatinisation), and the presence of fat, sugar, protein and fibre .

How to calculate the GI value of a meal ?

To date, only the GIs of single foods have been directly measured. In reality, it is more useful to know the GI of a meal, as we are more likely to eat combinations of foods. It is possible to estimate the GI of a meal by working out its total carbohydrate content, and then the contribution of each food to the total carbohydrate content.

Drawbacks of Glycemic Index 

The key to efficient glycogen refuelling and minimal fat storage  is to maintain steady levels of blood glucose and insulin. When glucose levels are high , large amounts of insulin are produced, which shunts the excess glucose into fat cells. 

However, it is the combined effect of a large amount of carbohydrate as well as a food’s GI value that really matters. The biggest drawback of the GI is that it doesn’t take account of the portion size you are eating. For example, many vegetables appear to have a high GI, which means they may be excluded on a low GI diet. 

However, their carbohydrate content is low and therefore their effect on blood glucose levels would be small. So despite having a high GI, the glycaemic load is low. 

Another drawback is that some high fat foods have a low GI, which gives a false impression of the food. 

For example, the GI of chips is lower than that of baked potatoes. Fat reduces the rate at which food is digested but high intakes of saturated and trans fats can increase blood cholesterol. It’s important you don’t select foods only by their GI — check the type of fat and avoid those that contain large amounts of saturated or trans fats.

Benefits of Low Glycemic Index Diet

A low glycemic index diet is very beneficial for glycogen recovery especially for athletes . Apart from this low GI diet also has many other health benefits . Low Glycemic Index foods or diets are highly recommended for people trying weight loss . When we switch to a low GI diet it gives feelings of satisfaction after eating , improves appetite and makes it easier to maintain healthy weight .

Apart from all these benefits a low GI diet can help you with followings mentioned below :-

  1. Reduce risk of Cardiovascular Diseases .
  2. Manage Type 2 Diabetes .
  3. Decrease Blood pressure .
  4. Increase resting metabolic rate .
  5. Manage metabolic syndrome .
  6. Manage cholesterol level .
  7. Prevent Polycystic ovary syndrome .

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Surajit jana

My name is Surajit Jana from India. I am an Electrical Engineer by profession. Bodybuilding and Fitness is my passion. I love being fit and have a good healthy physique. I have been in practice for the last 6 years. Now i think being fit myself should also help others to stay fit. The main purpose of creating and developing Health Image is to spread wellness knowledge and health awareness.

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