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Carbohydrates and the glycaemic index

Contents

Dietary nutrient groups
What is a healthy diet?
Body energy imbalance – a major health dilemma
Dietary carbohydrates and low glycaemic index foods
Achieving a low GI diet

 

Last partial update: July 2016 - Please read disclaimer before proceeding.

 

Dietary nutrient groups

The nutrients in food are divided into two main groups; those present in large amounts, called macronutrients, and those in small amounts, called micronutrients. The macronutrients consist of carbohydrates, fats, fibre and protein, while the micronutrients consist mainly of vitamins and minerals. The table below indicates the energy content and functions in the body of each of these groups. The roles nutrient groups play in causing and preventing illness in Western society are discussed in detail throughout this book. It needs to be emphasized that the majority of Australian diets are not nutrient deficient. In fact, most Australian diets contain too much energy and too much fat. There are, however, a few groups of people who are likely to have micronutrients deficiencies. This issue is discussed in the sections on micronutrients, vegetarian diets, and osteoporosis. The role of antioxidants in disease prevention is also discussed later in this section.

 

Function and energy content of nutrient groups
Nutrient	Foods sources	Energy content		Function / use
		cal	kJ
Fat - Fatty acids	Mainly animal sources and vegetable oils.	9	37	Mostly stored as fat for later energy use by the body when needed. Also an integral part of cell membranes.
Fat - Cholesterol	Lambs brains, liver, eggs and some seafood.			Synthesis of body compounds including cell membranes and body chemicals, such as steroid  hormones.
Alcohol	Alcoholic beverages	7	29	Used for energy. Alcohol is not converted to fat but is metabolized to provide energy before fat and thus reduces the rate of fat breakdown.
Protein	Meats, fish, poultry, eggs, milk products,  cereals, nuts and legumes, including soy beans, lentils, beans and peas	4	17	Mostly used in the synthesis of body components. Only rarely used as an energy source, such as in starvation.
Carbohydrate - Starches (complex carbohydrates)	Pasta, potato, breads, cereals, fruit, legumes	4	16	Provides energy for the body’s functions and some energy storage. It is usually stored as glycogen in the liver (and the muscle) but may be converted to fat if consumed in excess. (Glycogen is just many glucose molecules joined together.) The sugar that circulates in the blood and provides energy for the body is glucose. The brain relies almost solely on this glucose for energy and thus it is very important for blood glucose levels to be maintained.
Carbohydrate - Simple sugars  (sucrose, glucose, fructose, lactose)	Fruit, honey and other sweet syrups
Fibre	Bread, cereals, vegetables, fruit.	0	0	Fibre keeps the bowel functioning normally and has a role in protection of the bowel from cancer causing substances. Soluble fibre can reduce blood cholesterol levels.
Vitamins and minerals	A wide variety of foods is needed, especially vegetables, fruit, low-fat dairy and lean meat.	0	0	They are essential for the synthesis of many body components, especially enzymes. These nutrients have no significant energy function. Some are also important antioxidants.
Water	Fluids, fruit and vegetables	0	0	70% of the body is composed of water.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The major groups listed in the above table (and other nutrition topics) are dealt with in detail in other sections of this web site. (Links to these sections are listed below.)

• Fats
• Cholesterol
• Carbohydrates
• Vitamins and minerals
• Fibre
• Calcium and vitamin D intake
• Alcohol

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Body energy imbalance – a major health dilemma

One of the major problems associated with our modern, technologically-based society is that it has dramatically altered our body’s energy balance, unfortunately for the worse. We are doing less physical activity and have less time to prepare nutritious foods, relying instead on prepared food that usually has a high energy content. This combination of using less and consuming more energy means that many people have an energy intake in excess of their needs and this excess energy intake is stored as fat.

The contribution made by the different nutrient groups to this energy imbalance varies according to their energy content, with dietary fat being the main culprit. Table 8 shows that fat and alcohol have significantly higher energy content (per unit weight) than carbohydrate and protein. In addition to having a lower energy content, carbohydrates use up more body energy in the processes of being digested, stored (as fat or glycogen in the liver), and released for use in the body than fat does. It is an easy and efficient process for the body to store excess energy from dietary fat as fat in the body. The equivalent of only about 3 per cent of the energy provided by dietary fat is used in its storage as body fat. In contrast, about 25 per cent of the energy contained in the carbohydrate is used up in the process of converting it to stored fat. This is a much less efficient process and means that less fat will be created if excess energy is consumed in the form of dietary carbohydrate rather than dietary fat.

While alcohol is generally not stored as fat, the energy it provides means that less energy from dietary fat or dietary carbohydrate is needed for the body’s immediate energy demands, resulting in more being available for fat storage. Protein is rarely used to supply body energy. Starvation is one such time.

In an optimum diet, carbohydrate, mostly in the form of starch, contributes about 55 to 60 per cent of dietary energy intake and fat about 25 to 30 per cent. The other 15 per cent comes from protein. The contribution from alcohol varies according to consumption. Unfortunately, in modern western diets, the energy contribution from fat is more in the region of 35 per cent and the overall energy intake from all nutrients is excessive.

Reversing this energy imbalance is a major preventative health dilemma facing many Australians. It is dealt with in the sections on Obesity and Physical Inactivity.

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Dietary carbohydrates and low glycaemic index foods

The dietary advice advocated in this book centres around a low fat intake, especially low saturated fat, with the majority of dietary energy should be supplied by carbohydrates.

This section deals with choosing which carbohydrates people should include in their diet. Carbohydrates are divided into two main groups; sugars, which are simple compounds, and starches, which are more complex compounds made up from simple sugars. Together, they should provide about 60 per cent of dietary energy intake and the vast majority of this should come from starches.

Starch is the main carbohydrate found in cereal grains, root vegetables and pulses, and thus is the main constituent of our breads, pasta and cereals. It is broken down to simple sugars in the intestine and absorbed into the blood stream. Dietary sugars include sucrose (found in white and brown sugar, golden syrup, maple syrup, molasses and many fruits), fructose (found in ripe fruits, honey and some vegetables), lactose (found in milk), maltose (formed from the breakdown of starches) and glucose (found in sweet fruits and some vegetables). 

The sugar that circulates in the blood to provide energy to the body is glucose. This mainly comes from the breakdown of carbohydrates consumed in the diet and the breakdown of glucose that is stored in the liver as glycogen. (In most people, the body has enough glucose stored as glycogen to provide the energy required for about 90 minutes of vigorous exercise. Then glucose is sourced from the breakdown of fat stores.) Glucose is the brain’s only source of energy and for this reason the body regulates its level in the blood very carefully.

When choosing carbohydrates, several factors are important, including:

• The overall energy content of the food
• GI index
• Other beneficial nutrient content that is beneficial, especially vitamins and mineral, fibre
• Other beneficial nutrient content that is not beneficial, especially a high saturated fat content

In the past, complex carbohydrates have been advocated as being beneficial for health. This has been found to not necessarily be the case and the preferred way to classify all carbohydrates with regard to their health benefits is according to their glycaemic index (GI). The GI is a measure of how a particular carbohydrate containing food raises the body’s blood sugar (glucose) level after being consumed. It takes into account the degree to which it is raised and the duration of the rise. A high GI food is digested relatively quickly, thus raising your blood glucose quickly and to a higher peak level. A low GI food is digested more slowly, giving a slower, more sustained rise in blood glucose with a lower peak level. Foods are given a GI rating from 0 to 100. The food that gives the maximum overall rise in blood glucose is glucose itself and it is given a score of 100. The blood glucose responses of other foods are then compared to this level and given an appropriate score.

The body’s response to a rise in blood sugar is to increase the level of the hormone insulin. Insulin acts to move the sugar from the blood into cells (to be used later to provide energy) and thus reduces the sugar level in the blood. The important factor to note is that relatively more insulin is needed to reduce blood sugar after a high GI food than after a low GI food. Thus people who eat high a high glycaemic load diet (i.e. a diet with more carbohydrate-containing foods that have a higher GI) have a higher insulin requirement than people who eat a low glycaemic load diet (i.e. a diet with more carbohydrate-containing foods that have a lower GI). People who cannot produce enough insulin to cope with this additional requirement have glucose intolerance and may develop diabetes.

The increased insulin secretion associated with a diet containing a high glycaemic load also increases the risk of developing the metabolic syndrome, which includes problems such as obesity, coronary artery disease, hypertension and adverse changes in blood lipids, including raising blood triglyceride levels

In addition to reducing the likelihood of diabetes and the metabolic syndrome, the low, prolonged rise in blood sugar caused by low glycaemic load diets also helps to suppress the feeling of hunger longer, helping to reduce snacking and thus obesity. All this translates into the following health benefits for a low glycaemic load diet.

• Weight loss
• Improved blood lipids, particularly lower triglyceride levels.
• Reduced glucose intolerance and a decreased risk of developing diabetes
• Better control of diabetes in those with the disease
• Reduced risk of coronary heart disease (heart attacks).

It is important to note that, by necessity, GI figures are calculated when a single food is consumed. Meals are a combination of numerous food groups and the consumption of fats and proteins are likely to affect these GI levels. Thus, GI levels should be seen as a guide. Small differences in the GIs of particular foods are insignificant and need not affect food choices. However, choosing a food with a substantially lower GI than the alternative will be beneficial.

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Achieving a low GI diet

The glycaemic index has been calculated for over 700 foods and is available for many common foods on the Glycaemic Index website at http://www.gisymbol.com/?gclid=CK7j-MHUgM4CFYaYvAod-6wDFw or in many publications. They are also becoming commonly stated on food packaging. People should look for the ‘GI Symbol’, as this indicates that the GI value has been assessed by an accredited laboratory.

As a general indication, foods can be divided into three GI groups; low GI foods (GI value of 0 to 55), medium GI foods (GI value of 56 to 70) and high GI foods (GI value of 71 to 100). As stated above, it is important not to become too obsessed with GI values and to use them as a general guide to dietary habits. 

All foods have some carbohydrate, but most of our carbohydrate intake comes from bread, cereals, potatoes, rice and pasta. Therefore, it is these foods that people need to concentrate on when adding low GI foods to their diet.

 

Low glycaemic index (GI) foods (also low fat) Important:  The contribution of a food to the glycaemic load of a meal increases in proportion to the amount of carbohydrate it contains. The foods below are listed (approximately) in order of carbohydrate content, with foods having the highest content being at the top. Thus, foods near the top of the list are more important in reducing the glycaemic load than foods near the bottom. (This also means they contain more energy and this fact needs to be considered in dietary planning also.)
Breakfast		Lunch / dinner		Morning / afternoon tea
Food	GI	Food	GI	Food	GI
Muesli, natural All branTM cereal Porridge Special KTM Fruit loaf Bread, heavy mixed grain* Apple juice Orange juice Pineapple juice Milk, full cream Milk, skimmed Soy drink, So-goodTM Grapefruit Banana Apple Mangoes Kiwifruit Apricots, dried Peaches, canned	49 42 46 54 47 30-45 40 46 46 27 32 31 25 52 38 51 53 31 30	Rice (Doongara) Noodles (low fat) Fettuccine Spaghetti, white Spaghetti, wholemeal Vermicelli Ravioli Rice, basmati Tortellini Sushi Tomato soup, canned Corn (on cob) Bread, heavy mixed grain Yoghurt, low-fat flavoured Ice-cream, low fat Butter beans, boiled Chickpeas, boiled Baked beans Kidney beans, boiled Haricot beans, boiled Lentils, boiled	56 47 40 41 37 35 39 58 50 48-55 38 54 30-45 33 50 31 28 48 27 38 28	Apple muffin, low fat** Grapes Banana Pear Apple Mangoes Pop corn (natural) Fruit loaf Milk, skimmed Yoghurt, low-fat-fruit Soy drink, So-goodTM Orange Peach Plum Cherries	44 46 52 38 38 51 54 47 32 33 31 44 42 39 22
Note: The contribution of a food to the glycaemic load of a meal increases in proportion to the amount of carbohydrate it contains. The foods below are listed (approximately) in order of carbohydrate content, with foods having the highest content being at the top. Thus, foods near the top of the list are more important in reducing the glycaemic load than foods near the bottom. (This also means they contain more energy and this fact needs to be considered in dietary planning also. Sources: Brand-Miller, J and Forster-Powell, K. The New Glucose Revolution. Hodder, 1999 and the GI web site – www.glycemicindex.com.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The best way to reduce the dietary ‘glycaemic load’ is to include a large portion of at least one food that is high in carbohydrate and has a low GI food in each meal and include as many other low GI foods as possible. Consuming smaller meals more often rather than a few large meals also helps. Appropriate food choices for a good low GI diet include:

• a low GI breakfast cereal (that is also high in fibre), such as those based on wheat bran, barley and oats
• grainy breads
• pasta, sweet potato or couscous instead of normal potato
• low GI rice alternatives, such as Basmati, Doongara or wild rice instead of higher GI rices, such as brown, calrose or jasmine rice.
• barley, semolina, noodles and bulgar also have low GIs
• apples, oranges and pears instead of tropical fruit; less ripe fruits have a lower GI
• acidic foods, such as lemon juice, vinegar-based salad dressings, and sour dough breads.
• less refined/processed foods

When considering GIs, only compare the GIs of similar types of food; for example the GIs of two similar breads. Comparing GIs of icecream and bread would be inappropriate as they are completely different food choices.

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What is a healthy diet?

There are many nutritional factors that require consideration in formulating a healthy diet and these will be discussed in the rest of this section. Below is a table summarising what most nutritionists and dietitians would consider a healthy diet.

 

Recommended food intake for a healthy diet low in fat

Bread, pasta, potatoes (prepared without fat), grains Six serves a day. One serve equals one cup of mashed potato or cooked pasta or cooked rice, three quarters of a cup of breakfast cereal, or one slice of bread or fruit loaf or a small roll.

Meat, fish, chicken, eggs, legumes: Meat must be lean with all visible fat removed and chicken should be skinless. One serve a day. One serve equals 80g of red meat, 100g of cooked chicken or fish, one to two eggs, or 2/3 of a cup of cooked legumes. Foods should be prepared in as little fat as possible. Avoid frying / roasting.)

Vegetables Eat as much as liked, but at least 4 serves per day. One serve equals about half a cup or about 60 to90g. Try to make them the central part of at least some main meals. (For example, vegetarian lasagna or ratatouille.) A wide variety of vegetables is best. Adding a variety of herbs and spices (preferably fresh) to vegetarian dishes improves flavour and they should be an integral part these recipes. They are also nutritionally very beneficial.

Fruit Eat two to three serves a day. One serve equals one medium or 3 small (e.g. apricot) pieces of fruit, about 20 grapes, a cup of berries, or half a cup of canned/stewed fruit; about 120 to 140 g. Fruit is great after a meal or as a filler during the day.

Nuts A small handful several times a week (unsalted). Nuts, especially peanuts, should not be given to young children due to the risk of inhalation.

Milk products Two to three serves a day of low-fat dairy products. One serve equals one cup of low-fat milk or skim milk, or 200g of fat-reduced yoghurt. Low fat cheese is still relatively high in fat and should be used in moderation, Avoid butter and cream.

Fats and oils A maximum of two serves per day. One serve equals one teaspoon of oil for cooking, one teaspoon of margarine or a quarter of an avocado (50g). Monounsaturated oils are best. If using spreads, those containing plant sterols can help reduce cholesterol; or try using avocado.

Indulgences Enjoy a maximum of one to two serves each day. One serve equals two standard alcoholic drinks, a tablespoon of jam or honey, or one cup of home made popcorn. Try to avoid high-fat foods, such as potato or corn chips, sausage rolls and meat pies, chocolate, sweet biscuits and pastries. (For example, a commercially made muffin contains about 24g of fat and 2,200kJ of energy.)

Fluids Water is best. Try to drink at least two litres a day. A jug of iced water at every lunch or dinner should be a household ritual. Low-fat milk (as allowed above) is an equally good choice. A good way of ensuring an adequate calcium intake is to have two to three cups of calcium enriched low-fat milk per day. Alcohol needs to be restricted to two standard drinks per day and alcohol intake should be part of ‘indulgence allowances’. You should also have at least two alcohol free days a week. This does not mean no occasional nights out; although It is important not to increase the risk of harm when consuming alcohol. See section on alcohol use. ) Non-sweetened fruit juices should be restricted to one serve per day, about 150ml. Soft drinks and sweetened fruit juices need to be avoided.

 

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