The primary role of carbohydrates is to supply the body’s cells with glucose, which is the basic unit of carbohydrates and an important energy source. Nearly all of the energy required by the brain to function each day is supplied by glucose from the diet. Carbohydrates also maintain blood glucose levels and have a role in gastrointestinal health.

One gram of carbohydrate gives 16 kilojoules (kJ) or 3.75 calories of energy. At least half the energy in our diets should come from carbohydrate, mostly as complex carbohydrates. Sucrose (sugar) and other free sugars found in syrups and juices should be restricted to less than 10% of this energy because of the problems of excess energy intake.

Good sources of carbohydrate include grains, starchy vegetables, legumes and wholegrain cereals, all of which contain at least 3-15% complex carbohydrates. At least six servings of breads and cereal per day and at least three of vegetables and fruit per day are required to achieve a desirable carbohydrate intake.

Eat a variety of foods that provide carbohydrates, including breads, cereals and legumes.
Include wholemeal and wholegrain breads and cereals in the diet.
Eat plenty of fruits and vegetables.
Remember that plant foods such as cereals, breads, vegetables, fruits and legumes are good sources of dietary fibre.
Choose food and drinks which are low in sugar to avoid excess energy intake. Non-alcoholic beverages such as soft drinks and fruit juices contain high levels of sugar.
Honey, sweet spreads and dried fruits are concentrated sources of sugar.
High-sugar foods should be kept as treats.

In low carbohydrate diets, fruit, cereal, bread and vegetables are identified as the ‘bad foods’ as they contain carbohydrates, but there are serious consequences of removing these food products from the diet. In the short term their exclusion can lead to feeling run-down, a lack of energy and constipation. Long-term exclusion could lead to various conditions including kidney damage and high cholesterol. In fact, the long-term side-effects of a low carbohydrate diet are still not fully known.

Low carbohydrate diets can be very confusing and may lead to people cutting out healthy carbohydrate foods, i.e. fruit, vegetables, wholegrain, in favour of high-fat foods. The health benefits of fruit, vegetable and wholegrain include their high vitamin and mineral contents as well as fibre. High consumption of these foods can decrease risks of heart disease, diabetes and cancers.

There are some benefits of a high protein-low carbohydrate diet compared to a low fat-high carbohydrates diet with regards to speed of weight loss. Studies have shown that for the first 6 months, weight loss is more dramatic in the low carbohydrate diet but after a year the weight loss is the same, independent of which diet the person is following.

The safe amount of weight to lose per week is 1 kilogram. If a person is losing more than this amount a week it is likely that they are losing water and lean body mass rather than fat. It is important not to lose lean body mass as it then means the body requires less energy to maintain the same amount of weight, so a person has to eat less and less to lose more weight. Usually weight losses of more than 1 kilogram per week will not be sustainable and a person will end up putting the weight back on.

Fibre-rich foods in weight-reducing diets have fewer calories gram for gram than foods with high fat content and give a feeling of fullness and satiety. In low carbohydrate diets, there can be higher than usual intakes of saturated fats because high-protein foods may also contain high levels of fat. Diets containing high levels of fats can increase the risk of heart disease. Increased protein intake also causes an extra strain on the kidneys and can increase the amount of calcium excreted from the body, thereby affecting bone growth and restructure.

Following a diet with too many restrictions can be difficult to maintain. In the case of low carbohydrate diets the restriction on food choices means that the diet becomes dull and unpalatable, leading to a lack of motivation to continue and then a lapse back to unhealthy eating habits.

Many nutritionists would recommend that the most successful way to lose weight is by following a balanced diet which includes a moderate intake of a variety of foods. This diet needs to become a long-term lifestyle change rather than a diet. Although weight-loss results may be slower than a fad diet the long-term benefits are positive. It is better to balance calorie intake and exercise than to exclude carbohydrates altogether.

Fibre is a type of carbohydrate that cannot be digested in the stomach or small intestine but passes through to the large intestine. As fibre moves through the large intestine, bacteria break down much of the fibre. As they digest the fibre, these bacteria multiply and produce butyric acid, which has been shown to give protection against bowel cancer. Therefore consuming fibre is important for intestinal health. Fibre is found in all plants eaten for food, such as fruit, vegetables, grains and legumes.

Fibre is commonly categorised depending on how easily it dissolves in water. Soluble fibre partially dissolves in water and is found in oat bran, nuts, seeds, beans, apples and pears. This fibre has been shown to decrease the glycaemic index of carbohydrate foods by slowing the release of glucose from food. Insoluble fibre does not dissolve in water and is found in wholegrains, brown rice and a range of vegetables, including carrots and courgettes. Insoluble fibre is responsible for preventing and treating constipation.

Fibre appears to reduce the risk of various conditions, such as heart disease and type 2 diabetes.

Recommended daily intakes for fibre

It is recommended that New Zealanders should consume 25-30 grams of fibre per day. To achieve that amount of fibre it important to consume 5-6 servings of breads/cereals per day as well as at least three servings of vegetables per day. Some suggestions on how to increase fibre intake follow:

  • Eat some wholegrain breads and brown rice as well as white bread and white rice.
  • Eat whole fruits rather than fruit juices.
  • Choose wholegrain cereals at breakfast time.
  • Try raw vegetables for snacks rather than fatty or high-sugar snacks.
  • Keep the skins on fruit and vegetables.

All bread contains carbohydrate and fibre, so increasing your consumption of bread is a great way to increase your fibre intake. Although white bread provides a good source of soluble fibre, the breads containing the highest amount of fibre are wholemeal and mixed grain breads.

If you prefer white bread, then try one of the high-fibre white breads in which extra fibre has been added to the bread to double the amount of fibre present.

Eating foods high in dietary fibre can improve your overall diet too. Fibre is filling so it makes you feel more satisfied and less likely to snack on unhealthy foods in between meals.

The level of glucose in the blood is monitored and controlled by the action of a hormone called insulin. After consumption of carbohydrates, when levels of glucose are high in the blood, insulin signals to the body’s cells to absorb glucose for energy or storage. As the cells sponge up the blood glucose, levels of glucose in the blood fall back to the level that they were at before the food was eaten.

There are two types of diabetes. In Type 1 diabetes (also know as insulin dependent diabetes (IDDM)) the cells cannot absorb glucose as the body does not make enough insulin. This form of diabetes is treated with insulin injections. In Type 2 diabetes (also known as non insulin dependent diabetes (NIDDM)) the cells do not respond well to insulin’s signal to take up the blood glucose. This is called insulin resistance. The blood glucose and insulin levels remain at high levels in the blood and with time, insulin production stops. Type 2 diabetes has been linked to high blood pressure, a lowering of HDL cholesterol and heart disease.

Insulin resistance as seen in Type 2 diabetes is thought to be caused by a combination of genetic factors, a sedentary lifestyle, being overweight and a diet that encourages high levels of blood glucose after eating. To prevent the onset of Type 2 diabetes-people are encouraged to cut back on refined grains and eat more whole grains as part of a balanced diet. There is no evidence that high consumption of sugars causes diabetes, although Type 2 diabetes is associated with a person being overweight, which may be caused by over-consumption of high fat/sugar foods.

Symptoms of diabetes are often caused by the blood glucose level being raised above normal (hyperglycaemia). Symptoms are often severe and generally lead to a quick diagnosis. They may include tiredness, extreme weight loss, extreme thirst and frequent passing of urine.

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All foods that we eat contain energy and the amount of energy they contain and which is available to us is based on their composition and structure. The main components of foods are fat, protein, available carbohydrates, and/or fibre.

Foods which are mainly composed of fat, protein, available carbohydrates, and/or fibre, are more slowly broken down and give a sustained release of energy. However foods which contain a high sugar and/or carbohydrate that is readily digested are quickly broken down meaning that energy is rapidly available.
Glycaemic Response focuses on how quickly carbohydrate-rich foods are broken down in the gut and how quickly the energy from the carbohydrates present in these foods is released into the body’s blood stream as blood glucose for use throughout the whole body. How quickly this happens can be categorised by measurements of the body’s blood glucose levels.
Relative values for energy release to the body as blood glucose are determined using scientific tests which measure the effect of foods on blood glucose compared with the effect of glucose references.

The following information explains the different measures:

Glycaemic Index (GI)
The Glycaemic Index (GI) ranks carbohydrate-rich foods based on the effect that the carbohydrate present in the food has on blood glucose levels when consumed at equal carbohydrate intakes in the food.

The problem with GI is that although it is determined from measurements of blood glucose responses to the whole foods, the responses are attributed to the carbohydrate component of the food alone. GI is calculated as the response to a portion of food containing 50 g carbohydrate as a percentage of the response to 50 g glucose, so it allows you to compare carbohydrates in foods, and foods that contain equal amounts of carbohydrates.

However, not all foods or food portions contain the same quantity of carbohydrate so it makes comparisons between foods difficult. Also the GI of food does not change with quantity, so a muesli bar has a GI of 50 whether a person consumes 50 g or 80 g, meaning that the effect of serving size is neglected.

Glycaemic Load (GL)
Glycaemic Load is a new measure for assisting in making healthy food choices by being able to compare foods using a combination of the Glycaemic Index of the food and the amount of carbohydrate in the food. This measure gives an estimate of the relative glycaemic effect a food has on blood glucose expressed as Glycaemic Glucose Equivalents (GGE). If a portion of food has a GGE value of 8, it means it would have about the same effect on blood glucose as 8 g of glucose.

The following example explains how GL is more accurate than GI when presented with foods of different serve sizes and carbohydrate content. An average 58 g apricot and a 128 g banana have Glycaemic Indexes of 57 and 58 respectively. However, because a banana contains more carbohydrate and is twice the size of the apricot it will raise blood glucose levels six times higher than an apricot. This real difference in the glycaemic effects of a banana versus an apricot is reflected in their GL values; the GL of the 58 g apricot is 3, while the GL of the banana is 18. Hence the GL gives a better indication of the impact of the food item on blood glucose levels.

There are three categories of GL which foods can be classified into and a balanced diet should contain foods from all of these.

Low GL, but high carbohydrate foods assist in making you feel fuller for longer due to a lower and more sustained increase in blood glucose levels. This assists in controlling weight by making you feel less like snacking between meals. Including carbohydrate foods in the diet that give low blood glucose responses improves insulin sensitivity and decreases the risk of diabetes. Low GL foods are classified as containing 0 to 10 GGE/100g and examples are Multigrain bread (5), WeetBix (7) and raw apple (5).

Medium GL foods range from 11 to 19 GGE/100g and examples are Bread (Fibre white) (10), Molenberg Bread (10) and fresh orange juice (12).
High GL foods contain 20 GGE/100g or higher and examples are plain bagel (25), toasted sweetened muesli (25), and canned apricots (47). Diets containing large amounts of high-GL food have been associated with increased risk of diabetes and heart disease. For people with Type 2 diabetes, consuming a low-GL diet is one method of controlling their diabetes and general health as low-GL foods put less pressure on the requirements for insulin.

However an example of how low GL and high GL foods are an important part of a person’s diet is when you consider the requirements of a sports person. Sports people consume low-GL foods before an event to delay the time it takes to reach exhaustion point. However they also consume high-GL foods to reduce fatigue during an event and to help with recovery time afterwards.
Glycaemic Load offers a guide to choosing a variety of food combinations to make up a balanced diet and give a measure of the relative impact the food will have on blood glucose levels.