DISCOVER SCIENCE
We’re here to help athletes perform their best through the sharing of accurate and unbiased scientific information.
DISCOVER SCIENCE
We’re here to help athletes perform their best through the sharing of accurate and unbiased scientific information.
BASIC
B09 Not all carbs are the same
When ingested during exercise, some carbohydrates are fast while others are slow
BASIC
B09 Not all carbs are the same
When ingested during exercise, some carbohydrates are fast while others are slow
Introduction
It is generally accepted that carbohydrate intake during exercise can improve exercise performance lasting two hours or longer. There are many studies to support this. But there are far fewer studies about the best type of carbohydrate. Not all carbohydrates are digested, absorbed or used in the same way. There are however many studies that compared the use of carbohydrates ingested during exercise. Knowing this may is important because it was demonstrated that there is a dose response relationship between the amount of carbohydrate ingested and oxidized and performance during prolonged exercise. Therefore, it is important to identify carbohydrate sources that are used rapidly (we refer to this as exogenous (ingested) carbohydrate oxidation). The ideal carbohydrate during exercise is rapidly emptied from the stomach, does not need digestion or is digested very rapidly, is absorbed quickly and can immediately be used by the muscle. This blog is based on a large number of studies and references and the reader interested in more detail is referred to the review articles listed at the bottom of this blog.
Carbohydrate use from a drink is limited to 60 g/h
Many studies have shown that carbohydrates ingested during exercise can be used at a rate no higher than 1g/min (60g/h). This is independent of the type of carbohydrate: some are oxidized much less than 60 g/h, but no carbohydrate is oxidized at rates that exceed this. So even when you would ingest large amounts of glucose for example, say 100 g/h, no more than 60 g/h would be utilized. This is why may guidelines such as those published by the American College of Sports Medicine (ACSM) recommended athletes should consume carbohydrate up to 60g/h. In one study, carbohydrate was ingested at rates up to 3g/min (180g/h) (A “don’t try this at home” intake), the oxidation of the ingested carbohydrate did not exceed 1g/min (60g/h).
Differences between carbohydrates
Some carbohydrate are faster than others. The faster carbohydrates include glucose (grape sugar), sucrose (table sugar), maltose (milk sugar), maltodextrins and some starches. This blog compares the different types of carbohydrate and builds on an earlier blog on www.mysportscience.com
Misconceptions about complex carbs and sugar
Some complex carbohydrates (starches) can be oxidized at very high rates. So, it is a general misconception that complex carbohydrates are slow and simple carbohydrates are fast. Some carbohydrates, including simple sugars are slow. This includes fructose (fruit sugar), galactose and trehalose. There are also starches (those that are not very well soluble in water) that are slow. Thus, in general, we can divide carbohydrates in two categories: those oxidized at high rates and those used at low rates. Apparently, the digestion of maltodextrins (a chain of 10-20 glucose molecules) is not limiting and neither is the breakdown of the very large chain of glucose molecules in some starches. Fructose and galactose, however, are absorbed slower and need to be converted in the liver first before they can be used by the muscle. Some slower carbohydrates are limited because their digestion is slow, some because their absorption is slow and others because their conversion to a fuel the muscle can use is slow.
Fructose
If fructose is ingested at high rates (and it is not ingested with another carbohydrate), it is known to result in gastro-intestinal discomfort. The same has been observed for galactose. During exercise, it is recommended to choose a carbohydrate that is rapidly oxidized, so it does not accumulate in the intestine.
Rapid versus slow carbs
Most carbohydrate drinks on the market use glucose and sucrose as their main energy sources, others have used maltodextrins or starches that are rapidly used by the muscle. Some specifically use slow carbohydrates with the claim that this gives “sustained” energy. This is true if you only have one opportunity to ingested carbohydrates, but in most races or training where you can multiple feeding opportunities it is better not to let too much undigested or unabsorbed carbohydrate sit in your stomach or intestine.
Carbohydrates with different taste profiles
Carbohydrates also differ in their taste: glucose, fructose and sucrose are examples of very sweet carbohydrates (sugars). Maltodextrins and starches have very low levels of sweetness and in some cases no detectable sweetness at all.
Practical recommendation
The practical recommendations that resulted from these studies are simple:
- Use a carbohydrate that can be used rapidly (glucose, sucrose, maltodextrin or soluble starches)
- You deliver carbohydrates fast from drinks or gels (and even some solid sources if carefully selected).
- Ingest no more than 60g/h if you use a carbohydrate source that contains mostly one type of carbohydrate (recommendation 30-60g/h)
- Avoid drinks that contain only fructose or galactose or other carbohydrates that are slowly oxidized
References
Open Access (free) review articles on this topic:Jeukendrup A. A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Med. 2014 May;44 Suppl 1:S25-33.Jeukendrup AE. Nutrition for endurance sports: marathon, triathlon, and road cycling. J Sports Sci. 2011;29 Suppl 1:S91-9
Introduction
It is generally accepted that carbohydrate intake during exercise can improve exercise performance lasting two hours or longer. There are many studies to support this. But there are far fewer studies about the best type of carbohydrate. Not all carbohydrates are digested, absorbed or used in the same way. There are however many studies that compared the use of carbohydrates ingested during exercise. Knowing this may is important because it was demonstrated that there is a dose response relationship between the amount of carbohydrate ingested and oxidized and performance during prolonged exercise. Therefore, it is important to identify carbohydrate sources that are used rapidly (we refer to this as exogenous (ingested) carbohydrate oxidation). The ideal carbohydrate during exercise is rapidly emptied from the stomach, does not need digestion or is digested very rapidly, is absorbed quickly and can immediately be used by the muscle. This blog is based on a large number of studies and references and the reader interested in more detail is referred to the review articles listed at the bottom of this blog.
Carbohydrate use from a drink is limited to 60 g/h
Many studies have shown that carbohydrates ingested during exercise can be used at a rate no higher than 1g/min (60g/h). This is independent of the type of carbohydrate: some are oxidized much less than 60 g/h, but no carbohydrate is oxidized at rates that exceed this. So even when you would ingest large amounts of glucose for example, say 100 g/h, no more than 60 g/h would be utilized. This is why may guidelines such as those published by the American College of Sports Medicine (ACSM) recommended athletes should consume carbohydrate up to 60g/h. In one study, carbohydrate was ingested at rates up to 3g/min (180g/h) (A “don’t try this at home” intake), the oxidation of the ingested carbohydrate did not exceed 1g/min (60g/h).
Differences between carbohydrates
Some carbohydrate are faster than others. The faster carbohydrates include glucose (grape sugar), sucrose (table sugar), maltose (milk sugar), maltodextrins and some starches. This blog compares the different types of carbohydrate and builds on an earlier blog on www.mysportscience.com
Misconceptions about complex carbs and sugar
Some complex carbohydrates (starches) can be oxidized at very high rates. So, it is a general misconception that complex carbohydrates are slow and simple carbohydrates are fast. Some carbohydrates, including simple sugars are slow. This includes fructose (fruit sugar), galactose and trehalose. There are also starches (those that are not very well soluble in water) that are slow. Thus, in general, we can divide carbohydrates in two categories: those oxidized at high rates and those used at low rates. Apparently, the digestion of maltodextrins (a chain of 10-20 glucose molecules) is not limiting and neither is the breakdown of the very large chain of glucose molecules in some starches. Fructose and galactose, however, are absorbed slower and need to be converted in the liver first before they can be used by the muscle. Some slower carbohydrates are limited because their digestion is slow, some because their absorption is slow and others because their conversion to a fuel the muscle can use is slow.
Fructose
If fructose is ingested at high rates (and it is not ingested with another carbohydrate), it is known to result in gastro-intestinal discomfort. The same has been observed for galactose. During exercise, it is recommended to choose a carbohydrate that is rapidly oxidized, so it does not accumulate in the intestine.
Rapid versus slow carbs
Most carbohydrate drinks on the market use glucose and sucrose as their main energy sources, others have used maltodextrins or starches that are rapidly used by the muscle. Some specifically use slow carbohydrates with the claim that this gives “sustained” energy. This is true if you only have one opportunity to ingested carbohydrates, but in most races or training where you can multiple feeding opportunities it is better not to let too much undigested or unabsorbed carbohydrate sit in your stomach or intestine.
Carbohydrates with different taste profiles
Carbohydrates also differ in their taste: glucose, fructose and sucrose are examples of very sweet carbohydrates (sugars). Maltodextrins and starches have very low levels of sweetness and in some cases no detectable sweetness at all.
Practical recommendation
The practical recommendations that resulted from these studies are simple:
- Use a carbohydrate that can be used rapidly (glucose, sucrose, maltodextrin or soluble starches)
- You deliver carbohydrates fast from drinks or gels (and even some solid sources if carefully selected).
- Ingest no more than 60g/h if you use a carbohydrate source that contains mostly one type of carbohydrate (recommendation 30-60g/h)
- Avoid drinks that contain only fructose or galactose or other carbohydrates that are slowly oxidized
References
Open Access (free) review articles on this topic:Jeukendrup A. A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Med. 2014 May;44 Suppl 1:S25-33.Jeukendrup AE. Nutrition for endurance sports: marathon, triathlon, and road cycling. J Sports Sci. 2011;29 Suppl 1:S91-9