Mensagens
Glycemic
Index vs Glycemic Load
Over the last few years, the "glycemic index" concept was achieving an importance relevance. Not only exercisers but also everyone who's interested in Nutrition began to take into account this food aspect. However, taking glycemic index into account faces some problems, so there was the need to introduce the concept of "glycemic load". This post tries to dispel all doubts regarding these 2 terms so that they can be both used when we're talking about a healthy diet scenario.
Glycemic Index
What's glycemic index?
Glycemic index (GI) refers to the glucose level in one's blood and that is more or less constant between meals. GI is used to measure how fast glucose levels can raise (in one's blood) after eating some particular food. GI is defined by a numeric value between 0 and 100 (an easy scale to measure glucose level) and it can be grouped into 3 categories: Low (55 or less), Intermediate (56 to 69) and High (70 or more).
Is it important? Well, yes...
After all, knowing the food GI is important and there's no need to estimate values: all values are already calculated. The consumption of low-glycemic food causes a controlled and reduced increase of the glucose in bloodstream which also causes a small insulin peak; in turn, the consumption of high-glycemic food does exactly the opposite: raises blood glucose faster and increases the insulin peak.
Appendix:
What's insulin peak?
An insulin peak occurs when (beta-cells of) the pancreas detects a quick increase in blood glucose. That signal makes the pancreas to increase insulin hormone secretion (production) so that you're body is able to stabilize this glycaemia variation. Insulin helps to move glucose from the bloodstream to the muscles and other cells and, therefore, stabilizing its level.
If there's a quick and massive raise of glucose, there would be a bigger insulin production.
And what about the consequences?
The consequence is that if there's a greater need for insulin secretion, pancreas would need to work more and more.
This aspect is particularly relevant for type 2 diabetes patients because they may not produce enough insulin or if they do, their body cells may not be capable of processing it properly, leading to an inability of stabilizing the glucose level in the bloodstream (keeping it high), which their body may try to accomplish with compensatory mechanisms and leading to other medical problems.
The reverse effect:
When pancreas detects a high level of blood glucose it produces insulin. When, on the contrary, there's a decrease of the glucose level in the bloodstream (for example, during physical exercise) - event called hypoglycemia -, pancreas reduces insulin production and begins to produce other hormone: glucagon. Glucagon breaks down glycogen (stored form of glucose) in the liver. Then the liver releases glucose into the bloodstream in order to normalize its value.
It seems simple. Prioritize low-glycemic food and avoid the consumption of high-glycemic food. But then...
What's the problem about GI?
Well, there are several problems.
For a start, the GI of one meal isn't just the GI average of all foods in it. The protein and/or fat ... , fiber content, lower its GI. On the other hand, for example, the food high-heat processing increases its GI when comparing to that food in its natural form.
Another issue arises when we're talking about choosing food only regarding their GI. There are some foods with a low GI that if we only take into account that feature its consumption is harmless but their still loaded with fats. On the other hand, there are moments when the consumption of high-glycemic foods is not only harmless but advised, p.e., after workout.
And there's still the "amount" problem. The effect that 2 different foods with the same GI have on our body can be quite distinct and depends on the ingested amount, p.e., although rolled oats has a GI of 51 and pineapple a GI of 66, in order to get the same carbohydrates amount on 80g of oats, we'll have to eat half of a pineapple (450-500g) which is not only impractical but also harmful since pineapple is pretty sweet.
Glycemic index (GI) refers to the glucose level in one's blood and that is more or less constant between meals. GI is used to measure how fast glucose levels can raise (in one's blood) after eating some particular food. GI is defined by a numeric value between 0 and 100 (an easy scale to measure glucose level) and it can be grouped into 3 categories: Low (55 or less), Intermediate (56 to 69) and High (70 or more).
Is it important? Well, yes...
After all, knowing the food GI is important and there's no need to estimate values: all values are already calculated. The consumption of low-glycemic food causes a controlled and reduced increase of the glucose in bloodstream which also causes a small insulin peak; in turn, the consumption of high-glycemic food does exactly the opposite: raises blood glucose faster and increases the insulin peak.
Appendix:
What's insulin peak?
An insulin peak occurs when (beta-cells of) the pancreas detects a quick increase in blood glucose. That signal makes the pancreas to increase insulin hormone secretion (production) so that you're body is able to stabilize this glycaemia variation. Insulin helps to move glucose from the bloodstream to the muscles and other cells and, therefore, stabilizing its level.
If there's a quick and massive raise of glucose, there would be a bigger insulin production.
And what about the consequences?
The consequence is that if there's a greater need for insulin secretion, pancreas would need to work more and more.
This aspect is particularly relevant for type 2 diabetes patients because they may not produce enough insulin or if they do, their body cells may not be capable of processing it properly, leading to an inability of stabilizing the glucose level in the bloodstream (keeping it high), which their body may try to accomplish with compensatory mechanisms and leading to other medical problems.
The reverse effect:
When pancreas detects a high level of blood glucose it produces insulin. When, on the contrary, there's a decrease of the glucose level in the bloodstream (for example, during physical exercise) - event called hypoglycemia -, pancreas reduces insulin production and begins to produce other hormone: glucagon. Glucagon breaks down glycogen (stored form of glucose) in the liver. Then the liver releases glucose into the bloodstream in order to normalize its value.
It seems simple. Prioritize low-glycemic food and avoid the consumption of high-glycemic food. But then...
What's the problem about GI?
Well, there are several problems.
For a start, the GI of one meal isn't just the GI average of all foods in it. The protein and/or fat ... , fiber content, lower its GI. On the other hand, for example, the food high-heat processing increases its GI when comparing to that food in its natural form.
Another issue arises when we're talking about choosing food only regarding their GI. There are some foods with a low GI that if we only take into account that feature its consumption is harmless but their still loaded with fats. On the other hand, there are moments when the consumption of high-glycemic foods is not only harmless but advised, p.e., after workout.
And there's still the "amount" problem. The effect that 2 different foods with the same GI have on our body can be quite distinct and depends on the ingested amount, p.e., although rolled oats has a GI of 51 and pineapple a GI of 66, in order to get the same carbohydrates amount on 80g of oats, we'll have to eat half of a pineapple (450-500g) which is not only impractical but also harmful since pineapple is pretty sweet.
Glycemic Load
What's glycemic load?
The concept of glycemic load (GL) only appeared recently (15-20 years) and aims to address the shortcoming of the glycemic index. GL takes into account the ingestion of some particular food (per serving). Like GI, it can be grouped into 3 categories: Low (0 to 10), Intermediate (11 to 19) and High (20 or more). The formula is as follows:
The concept of glycemic load (GL) only appeared recently (15-20 years) and aims to address the shortcoming of the glycemic index. GL takes into account the ingestion of some particular food (per serving). Like GI, it can be grouped into 3 categories: Low (0 to 10), Intermediate (11 to 19) and High (20 or more). The formula is as follows:
GL = GI/100 x Carbs(g) per serving
What's the advantage of using GL?
With GL we estimate the insulin answer of our body taking into account the type and amount of the ingested food (although we use carbs amount of that food).
Now, while using GL, the last spotted problem regarding GI is solved.
Example:
GL(Rolled oats) = 51/100 x 56 = 28.6
GL(Pineapple) = 66/100 x 28 = 18.5
Now we can see that glycemic load of rolled oats is higher than the glycemic load of pineapples and we can now prove the difference that one serving of each of these food has on our glucose level.
Conclusions:
As we could see, using glycemic load instead of glycemic index delivers a more precise and accurate notion about the role that each food plays when we're talking about glycaemia. However, due to still using GI, GL still faces some commonly issues. Nevertheless, and to answer to the post title, Glycemic Load comes out as the winner from the fight Glycemic Index vs Glycemic Load.
Sources:
http://www.glycemicindex.com/
http://www.diabetes.org/food-and-fitness/food/what-can-i-eat/understanding-carbohydrates/glycemic-index-and-diabetes.html
http://www.health.harvard.edu/newsweek/Glycemic_index_and_glycemic_load_for_100_foods.htm
http://www.whfoods.com/genpage.php?tname=faq&dbid=32
http://saude.sapo.pt/peso-nutricao/dietas/lista-dietas-A-Z/carga-glicemica-baixa-dieta.html
http://www.fat-new-world.com/2011/05/o-indice-glicemico-e-secrecao-de.html
http://www.gisymbol.com/about/glycemic-index/
http://www.webmd.com/diet/glycemic-index-diet
http://lpi.oregonstate.edu/infocenter/foods/grains/gigl.html
http://www.montignac.com/en/the-glycemic-index-concept/
http://www.diabetes.co.uk/diet/glycemic-index-range.html
http://www.mydr.com.au/gastrointestinal-health/pancreas-and-insulin
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Índice
Glicémico vs Carga Glicémica
Nos últimos anos, o termo "índice glicémico" foi ganhando uma relevância importante. Não apenas os praticantes de exercício, mas também todos os que se interessam por Nutrição começaram a ter em consideração este aspecto dos alimentos. No entanto, ter em consideração o índice glicémico tem alguns problemas, sendo então necessário introduzir o conceito de "carga glicémica". Este post tenta dissipar as dúvidas em relação a estes 2 termos para que ambos possam ser usados num cenário de alimentação saudável.
Índice Glicémico
O que é índice glicémico?
O índice glicémico (IG) refere-se ao nível de glicose presente no sangue que é mais ou menos constante entre refeições. O IG é utilizado para medir a rapidez com que os níveis de glicose sobem (no sangue) após a ingestão de um determinado alimento. O IG mede-se através de um valor numérico entre 0 e 100 (uma "escala" fácil para a referida rapidez) e pode ser agrupado em 3 categorias: Baixo (55 ou menos), Intermédio (56 a 69) e Alto (70 ou mais).
É importante? Bem, sim...
De facto, conhecer o IG dos alimentos é importante e não é necessário qualquer cálculo: os valores estão tabelados a priori. O consumo de alimentos com baixo IG provoca um reduzido e controlado aumento da glicose na corrente sanguínea, o que resulta num reduzido pico insulínico; por sua vez, o consumo de alimentos com alto IG faz naturalmente exactamente o oposto: aumenta mais rapidamente a glicose no sangue, aumentando o pico insulínico.
Apêndice
O que é o pico insulínico?
O pico insulínico ocorre quando (as células-beta) do pâncreas detecta que existe um rápido e grande aumento de glicose no sangue. Esse sinal leva a que o pâncreas aumente a secreção (produção) de uma hormona chamada insulina para estabilizar essa variação de glicémia. A insulina ajuda a glicose a sair da corrente sanguínea para os músculos e outras células, estabilizando o seu nível.
Maior e mais rápido aumento de glicose, maior produção de insulina.
E existem consequências?
A consequência é que quanto maior for a necessidade de secreção de insulina, maior vai ser o trabalho que o pâncreas tem de fazer.
Este aspecto assume particular relevância para os doentes com diabetes tipo 2, pois podem não produzir insulina em quantidade suficiente ou, caso produzam, as células do seu corpo podem não ter a capacidade de a processar devidamente, levando a que não consigam estabilizar o nível de glicose na corrente sanguínea (mantendo-se alto), tentando o organismo fazê-lo por via de outros mecanismos compensatórios e levando a outros problemas médicos.
O efeito inverso:
Quando o pâncreas detecta um nível elevado de glicose no sangue, produz insulina. Quando, pelo contrário, existe uma redução do nível de glicose na corrente sanguínea (por exemplo, durante a prática de exercício físico) - chamada hipoglicémia -, o pâncreas reduz a produção de insulina e estimula a produção de outra hormona: o glucagão. O glucagão degrada o glicogénio (guardado em forma de glicose) no fígado. Depois, o fígado liberta a glicose na corrente sanguínea, a fim de normalizar o valor da mesma.
Parece simples. Privilegiar alimentos com baixo IG e evitar o consumo dos que têm alto IG. Mas, então...
Qual é o problema do IG?
Bom, são vários problemas.
Para começar, o IG de uma refeição não é somente a média dos IG's dos alimentos que a constituem. A adição de proteína e/ou gordura a um hidrato de carbono, assim como o teor de fibra, diminuem o seu IG. Por outro lado, o processamento de alimentos a altas temperaturas, por exemplo, aumenta o IG desse alimento, em relação ao seu estado "normal".
Outro problema é o de escolher os alimentos baseando-se apenas no IG. Existem alimentos de baixo IG que se considerarmos apenas este factor o seu consumo é inócuo, mas que têm um alto teor de gordura. Por outro lado, existem momentos em que o consumo de alimentos com alto IG não só é inofensivo como aconselhado, p.ex., no pós-treino.
Para terminar, existe ainda o problema das "quantidades". O efeito que 2 alimentos diferentes com o mesmo IG podem ter no nosso organismo depende da quantidade ingerida e que pode ser bastante díspar, p.ex., embora a aveia tenha um IG de 51 e o ananás um IG de 66, para conseguirmos uma quantidade de HC's equivalente a 80g de aveia teríamos de comer 1/2 ananás (450-500g), o que é impraticável e prejudicial, pois o ananás até é bastante doce.
Carga Glicémica
O que é a carga glicémica?
O conceito de carga glicémica (CG) apenas surgiu recentemente (15-20 anos) e pretende colmatar algumas falhas do índice glicémico. A CG tem em conta a ingestão de uma porção definida de um alimento em particular. Como o IG, pode ser agrupada em 3 categorias: Baixa (0 a 10), Intermédia (11 a 19) e Alta (20 ou mais). A fórmula é a seguinte:
CG = IG/100 x HC(g) por porção
Qual a vantagem de utilizar a CG?
Com a CG calculamos a resposta insulínica do nosso organismo tendo em conta o tipo e a quantidade do alimento ingerido (embora utilizemos a quantidade de HC's desse alimento).
Agora, ao utilizar a CG, o último problema identificado relativamente ao IG fica resolvido.
Exemplo:
CG(Aveia) = 51/100 x 56 = 28.6
CG(Ananás) = 66/100 x 28 = 18.5
Agora podemos ver que a carga glicémica da aveia é superior à do ananás e comprovamos a diferença que uma dose de cada um destes alimentos tem no nosso nível de glicose.
Conclusões:
Como pudemos ver, a utilização da carga glicémica em vez do índice glicémico é mais precisa e dá uma noção mais concreta do papel que cada alimento desempenha quando falamos de glicémia. No entanto, por utilizar o IG, continua a ter alguns problemas em comum. Ainda assim, e para responder ao título do post, no combate Índice Glicémico vs Carga Glicémica, a Carga Glicémica sai vencedora.
Fontes:
http://www.glycemicindex.com/
http://www.diabetes.org/food-and-fitness/food/what-can-i-eat/understanding-carbohydrates/glycemic-index-and-diabetes.html
http://www.health.harvard.edu/newsweek/Glycemic_index_and_glycemic_load_for_100_foods.htm
http://www.whfoods.com/genpage.php?tname=faq&dbid=32
http://saude.sapo.pt/peso-nutricao/dietas/lista-dietas-A-Z/carga-glicemica-baixa-dieta.html
http://www.fat-new-world.com/2011/05/o-indice-glicemico-e-secrecao-de.html
http://www.gisymbol.com/about/glycemic-index/
http://www.webmd.com/diet/glycemic-index-diet
http://lpi.oregonstate.edu/infocenter/foods/grains/gigl.html
http://www.montignac.com/en/the-glycemic-index-concept/
http://www.diabetes.co.uk/diet/glycemic-index-range.html
http://www.mydr.com.au/gastrointestinal-health/pancreas-and-insulin
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