Please Scroll Down to See Forums Below 
southpaw45
New member
After reading dbbt's post about post workout nutrition, one part always confuses me - GI carbs. This comes up in a lot articles about nutrition so its good to know about it. Here's a really good article on it:
Glycemic index (abbreviated to GI) is a way of classifying carbohydrate foods according to their effect on blood glucose. It is of special significance to people with diabetes, but there is also evidence that GI has health implications for people in general.
When a food containing carbohydrate is eaten it is digested in the small intestine and sugars are released from the carbohydrate. Glucose is the major sugar, but other sugars are also released and then absorbed into the blood, along with the glucose. The body responds to the increase in blood glucose by releasing insulin—a hormone that (among other metabolic functions) causes the glucose to be stored for later use. GI is a measure of how long it takes for the glucose from a food to be absorbed into the blood. The lower the GI, the slower and more even the rate of absorption of glucose into the blood. In essence, a food with a low GI means ‘slow release’ of carbohydrate into the body, while high GI means the carbohydrate is rapidly released. (See Appendix 1 for a technical description of how GI is determined for individual foods.)
People who have diabetes cannot produce enough insulin, or the insulin they produce is not fully effective, so their blood glucose may not be maintained within the limits that are optimal for both short- and long-term health. It is in this regard that GI is believed to be of greatest value because, following a meal or snack, low GI foods lead to more even blood glucose levels than do high GI foods.
GI is a fairly recent concept. Before the GI was devised, nutritionists divided carbohydrates into 'complex' and 'simple' forms. This is a division based on chemical structure: in essence, complex carbohydrates are starch, while simple carbohydrates are sugars. (See Appendix 2 for more detailed information on this.) Examples of foods with high levels of complex carbohydrate are bread, rice, potatoes and pasta. Examples of foods with entirely simple carbohydrate are sucrose (commonly called 'sugar') and honey. Also, most of the carbohydrate in milk and fruit is simple carbohydrate (while vegetables are more likely to have complex carbohydrate).
Nutritionists used to believe that it would take longer to digest and absorb complex carbohydrates than simple carbohydrates. So foods rich in complex carbohydrate were thought to be preferable for people with diabetes (because slow absorption avoids any sudden rise in blood glucose, as previously mentioned). In the last decade or so, it has been found that some foods with a relatively high content of simple carbohydrates (e.g. those in milk and fruits) have lower GI than many foods that have mainly complex carbohydrates (e.g., potatoes and rice). There can also be substantial differences in GI between closely related foods (e.g. mixed grain bread has a lower GI than either white or wholemeal bread). The old, simplistic concept of 'complex carbohydrate good, simple carbohydrate bad' is being replaced with the idea that low GI foods may generally be better than high GI foods within particular food categories.
However, on its own the GI of a food does not make it ‘good’ or ‘bad’. Some high GI foods (e.g. potato and watermelon) still make a valuable nutritional contribution to our diet, while some low GI foods (e.g. corn chips and chocolate—both of which are high in saturated fat) are not considered to be particularly health promoting, despite their low GI. So although GI is believed to be important, it is only one characteristic of nutritional significance for a food.
Low GI foods (GI of 55 or less) include most mixed-grain breads, white and wholemeal spaghetti, All Bran, legumes (peas, beans, soy products), milk and yogurt, ice-cream, rolled oats, toasted muesli and most fruits. Intermediate GI foods (GI in the range 56-69) include Swiss formula muesli, white durum wheat spaghetti, 'sugar' (sucrose), raisins and sultanas, Basmati, Arborio and long-grain rice and muesli bars. High GI foods (GI of 70 or more) include white and wholemeal bread, potatoes (boiled and baked), white Jasmine rice, some breakfast cereals (e.g., Cornflakes, Coco Pops) and sports drinks.
But these foods are not often eaten on their own. Usually, people will eat them as part of a mixed meal. It turns out that many factors influence the GI of a meal, including the amount of protein and fat eaten, the type of starch (see Appendix 3 for more information on this) and the quantities and types of dietary fibre. There is evidence, however, that including low GI foods in a meal will reduce the overall GI of that meal.
Although there is certainly room for some high and intermediate GI foods in any balanced diet, many nutritionists now accept that encouraging people to eat low GI foods will be beneficial. Eating mainly low GI foods may be useful not only for people with diabetes, but also in the prevention and/or treatment of heart disease and obesity—low GI diets have been reported to lead to improved insulin responses and better blood lipid profiles (i.e. improved blood cholesterol and triglycerides). Also, because the carbohydrate is absorbed slowly from low GI foods, they may help with weight management by delaying the return of hunger (which is thought to be triggered by a reduced blood glucose level, among many other factors).
A recent variation on the GI concept is that of ‘glycemic load’ (GL) of a food or mixed meal. The GL takes into account both the rate of release (GI) and the total amount of the carbohydrate in a food or mixed meal (see Appendix 4 for a technical description of how GL is determined). For example, a carrot and a fruit muffin (e.g. apple muffin) both have a GI of about 50. But a fruit muffin contains far more carbohydrate than an equivalent weight of carrot, so the muffin has a much greater GL.
A high GL will inevitably result from eating a lot of high GI carbohydrate foods—e.g. most breakfast cereals, smooth-textured bread, short-grain rice, potatoes, most biscuits and crackers.
But it is important to realise that eating small amounts of high GI carbohydrate foods is unlikely to have a big impact on blood glucose and insulin levels, while consuming large quantities of relatively low GI carbohydrate foods—e.g. pasta, wholegrain bread and toasted muesli—can still raise blood glucose and insulin levels significantly.
Regardless of how it occurs, a high GL meal or substantial snack leads to a large rise in blood glucose level, which leads in turn to increased requirement for insulin.
Reducing GL can be achieved in several ways. For example, low GI foods can replace high GI equivalents (as examples, eat long-grain Basmati rice instead of short-grain rice; replace white bread with grainy bread; eat fewer potatoes and increase consumption of pasta). Alternatively, or in addition, the GL of the diet can be reduced by cutting back a little on high GI carbohydrate foods (such as white bread, short-grained rice and potato) and increasing intake of low carbohydrate foods such as leafy-green and orange-yellow vegetables, fruits and appropriate protein foods (e.g. fish, lean meat, peas, beans and other legumes).
GI/GL is also believed to be of significance in sports performance. The 'pre-game' meal is likely to be of greatest value if it is eaten several hours before the event and contains plenty of low and medium GI foods (such as pasta, dried apricots, bananas, yoghurt). Eating easily digested, medium and high GI foods (e.g. sports drinks, carbohydrate bars, jelly beans) during an endurance event will provide a rapid resupply of glucose to the working muscles. Consuming relatively high GI foods soon after the event will help to replenish carbohydrate stores.
Appendix 1 How GI is determined
The GI of a food is determined by measuring how rapidly glucose is absorbed from the intestine into the blood when the quantity of the food that contains 50 g of carbohydrate is eaten, relative to the rate of glucose absorption that results from eating 50 g of pure glucose. This is expressed as a percentage. So a food that leads to exactly the same rate of release of glucose as feeding with plain glucose has a GI of 100; a food that releases glucose at half the rate has a GI of 50; a food that releases glucose 20% faster has a GI of 120, and so on.
Appendix 2
Complex versus simple carbohydrates
Starch consists of many molecules of a simple sugar (glucose) chemically bound together. Simple carbohydrates, on the other hand, have the glucose (or other sugars) as individual molecules, or at most, as two molecules chemically bound together. For example, glucose and fructose are simple carbohydrates that exist as individual molecules (in honey, for example). Common 'sugar' (known to nutritionists and chemists as 'sucrose') is an example of a simple carbohydrate that consists of two molecules, glucose and fructose, chemically bound together.
Bread, rice and potatoes are starchy foods (and therefore complex carbohydrate foods) while sucrose, honey and milk sugar ('lactose') are simple carbohydrates. Fruits provide most of their carbohydrate in the form of simple carbohydrate (mostly fructose).
Appendix 3
Effects of different types of starch on GI
There are two forms of starch—'amylose' and 'amylopectin'. Amylopectin is broken down in the intestine and absorbed more rapidly into the blood than is amylose. This partly explains why apparently nutritionally-similar foods such as pasta and rice (for example) can have quite different GI values: rice is higher in amylopectin and lower in amylose than is pasta, so rice has the higher GI.
Appendix 4
How is the Glycemic Load (GL) calculated
The GL of a food is determined by multiplying the GI value of the food by the quantity of carbohydrate per serve, and then dividing by 100.
For example, a slice of white bread contains about 15 g of carbohydrate, and the GI of white bread is 70. So the GL of a slice of white bread = (15 x 70/100)
= 10.5
If you were to choose stoneground wholemeal instead, the GL would be 5.8, only about half the value for white bread.
To calculate the GL of a meal, nutritionists add together the individual GL of each component of that meal. For example, the GL of a light meal consisting of two slices of white bread, 220 mL of canned split pea soup and an average apple would be ~35.
-Australian Nutrition
Glycemic index (abbreviated to GI) is a way of classifying carbohydrate foods according to their effect on blood glucose. It is of special significance to people with diabetes, but there is also evidence that GI has health implications for people in general.
When a food containing carbohydrate is eaten it is digested in the small intestine and sugars are released from the carbohydrate. Glucose is the major sugar, but other sugars are also released and then absorbed into the blood, along with the glucose. The body responds to the increase in blood glucose by releasing insulin—a hormone that (among other metabolic functions) causes the glucose to be stored for later use. GI is a measure of how long it takes for the glucose from a food to be absorbed into the blood. The lower the GI, the slower and more even the rate of absorption of glucose into the blood. In essence, a food with a low GI means ‘slow release’ of carbohydrate into the body, while high GI means the carbohydrate is rapidly released. (See Appendix 1 for a technical description of how GI is determined for individual foods.)
People who have diabetes cannot produce enough insulin, or the insulin they produce is not fully effective, so their blood glucose may not be maintained within the limits that are optimal for both short- and long-term health. It is in this regard that GI is believed to be of greatest value because, following a meal or snack, low GI foods lead to more even blood glucose levels than do high GI foods.
GI is a fairly recent concept. Before the GI was devised, nutritionists divided carbohydrates into 'complex' and 'simple' forms. This is a division based on chemical structure: in essence, complex carbohydrates are starch, while simple carbohydrates are sugars. (See Appendix 2 for more detailed information on this.) Examples of foods with high levels of complex carbohydrate are bread, rice, potatoes and pasta. Examples of foods with entirely simple carbohydrate are sucrose (commonly called 'sugar') and honey. Also, most of the carbohydrate in milk and fruit is simple carbohydrate (while vegetables are more likely to have complex carbohydrate).
Nutritionists used to believe that it would take longer to digest and absorb complex carbohydrates than simple carbohydrates. So foods rich in complex carbohydrate were thought to be preferable for people with diabetes (because slow absorption avoids any sudden rise in blood glucose, as previously mentioned). In the last decade or so, it has been found that some foods with a relatively high content of simple carbohydrates (e.g. those in milk and fruits) have lower GI than many foods that have mainly complex carbohydrates (e.g., potatoes and rice). There can also be substantial differences in GI between closely related foods (e.g. mixed grain bread has a lower GI than either white or wholemeal bread). The old, simplistic concept of 'complex carbohydrate good, simple carbohydrate bad' is being replaced with the idea that low GI foods may generally be better than high GI foods within particular food categories.
However, on its own the GI of a food does not make it ‘good’ or ‘bad’. Some high GI foods (e.g. potato and watermelon) still make a valuable nutritional contribution to our diet, while some low GI foods (e.g. corn chips and chocolate—both of which are high in saturated fat) are not considered to be particularly health promoting, despite their low GI. So although GI is believed to be important, it is only one characteristic of nutritional significance for a food.
Low GI foods (GI of 55 or less) include most mixed-grain breads, white and wholemeal spaghetti, All Bran, legumes (peas, beans, soy products), milk and yogurt, ice-cream, rolled oats, toasted muesli and most fruits. Intermediate GI foods (GI in the range 56-69) include Swiss formula muesli, white durum wheat spaghetti, 'sugar' (sucrose), raisins and sultanas, Basmati, Arborio and long-grain rice and muesli bars. High GI foods (GI of 70 or more) include white and wholemeal bread, potatoes (boiled and baked), white Jasmine rice, some breakfast cereals (e.g., Cornflakes, Coco Pops) and sports drinks.
But these foods are not often eaten on their own. Usually, people will eat them as part of a mixed meal. It turns out that many factors influence the GI of a meal, including the amount of protein and fat eaten, the type of starch (see Appendix 3 for more information on this) and the quantities and types of dietary fibre. There is evidence, however, that including low GI foods in a meal will reduce the overall GI of that meal.
Although there is certainly room for some high and intermediate GI foods in any balanced diet, many nutritionists now accept that encouraging people to eat low GI foods will be beneficial. Eating mainly low GI foods may be useful not only for people with diabetes, but also in the prevention and/or treatment of heart disease and obesity—low GI diets have been reported to lead to improved insulin responses and better blood lipid profiles (i.e. improved blood cholesterol and triglycerides). Also, because the carbohydrate is absorbed slowly from low GI foods, they may help with weight management by delaying the return of hunger (which is thought to be triggered by a reduced blood glucose level, among many other factors).
A recent variation on the GI concept is that of ‘glycemic load’ (GL) of a food or mixed meal. The GL takes into account both the rate of release (GI) and the total amount of the carbohydrate in a food or mixed meal (see Appendix 4 for a technical description of how GL is determined). For example, a carrot and a fruit muffin (e.g. apple muffin) both have a GI of about 50. But a fruit muffin contains far more carbohydrate than an equivalent weight of carrot, so the muffin has a much greater GL.
A high GL will inevitably result from eating a lot of high GI carbohydrate foods—e.g. most breakfast cereals, smooth-textured bread, short-grain rice, potatoes, most biscuits and crackers.
But it is important to realise that eating small amounts of high GI carbohydrate foods is unlikely to have a big impact on blood glucose and insulin levels, while consuming large quantities of relatively low GI carbohydrate foods—e.g. pasta, wholegrain bread and toasted muesli—can still raise blood glucose and insulin levels significantly.
Regardless of how it occurs, a high GL meal or substantial snack leads to a large rise in blood glucose level, which leads in turn to increased requirement for insulin.
Reducing GL can be achieved in several ways. For example, low GI foods can replace high GI equivalents (as examples, eat long-grain Basmati rice instead of short-grain rice; replace white bread with grainy bread; eat fewer potatoes and increase consumption of pasta). Alternatively, or in addition, the GL of the diet can be reduced by cutting back a little on high GI carbohydrate foods (such as white bread, short-grained rice and potato) and increasing intake of low carbohydrate foods such as leafy-green and orange-yellow vegetables, fruits and appropriate protein foods (e.g. fish, lean meat, peas, beans and other legumes).
GI/GL is also believed to be of significance in sports performance. The 'pre-game' meal is likely to be of greatest value if it is eaten several hours before the event and contains plenty of low and medium GI foods (such as pasta, dried apricots, bananas, yoghurt). Eating easily digested, medium and high GI foods (e.g. sports drinks, carbohydrate bars, jelly beans) during an endurance event will provide a rapid resupply of glucose to the working muscles. Consuming relatively high GI foods soon after the event will help to replenish carbohydrate stores.
Appendix 1 How GI is determined
The GI of a food is determined by measuring how rapidly glucose is absorbed from the intestine into the blood when the quantity of the food that contains 50 g of carbohydrate is eaten, relative to the rate of glucose absorption that results from eating 50 g of pure glucose. This is expressed as a percentage. So a food that leads to exactly the same rate of release of glucose as feeding with plain glucose has a GI of 100; a food that releases glucose at half the rate has a GI of 50; a food that releases glucose 20% faster has a GI of 120, and so on.
Appendix 2
Complex versus simple carbohydrates
Starch consists of many molecules of a simple sugar (glucose) chemically bound together. Simple carbohydrates, on the other hand, have the glucose (or other sugars) as individual molecules, or at most, as two molecules chemically bound together. For example, glucose and fructose are simple carbohydrates that exist as individual molecules (in honey, for example). Common 'sugar' (known to nutritionists and chemists as 'sucrose') is an example of a simple carbohydrate that consists of two molecules, glucose and fructose, chemically bound together.
Bread, rice and potatoes are starchy foods (and therefore complex carbohydrate foods) while sucrose, honey and milk sugar ('lactose') are simple carbohydrates. Fruits provide most of their carbohydrate in the form of simple carbohydrate (mostly fructose).
Appendix 3
Effects of different types of starch on GI
There are two forms of starch—'amylose' and 'amylopectin'. Amylopectin is broken down in the intestine and absorbed more rapidly into the blood than is amylose. This partly explains why apparently nutritionally-similar foods such as pasta and rice (for example) can have quite different GI values: rice is higher in amylopectin and lower in amylose than is pasta, so rice has the higher GI.
Appendix 4
How is the Glycemic Load (GL) calculated
The GL of a food is determined by multiplying the GI value of the food by the quantity of carbohydrate per serve, and then dividing by 100.
For example, a slice of white bread contains about 15 g of carbohydrate, and the GI of white bread is 70. So the GL of a slice of white bread = (15 x 70/100)
= 10.5
If you were to choose stoneground wholemeal instead, the GL would be 5.8, only about half the value for white bread.
To calculate the GL of a meal, nutritionists add together the individual GL of each component of that meal. For example, the GL of a light meal consisting of two slices of white bread, 220 mL of canned split pea soup and an average apple would be ~35.
-Australian Nutrition
