Carbohydrates and the Glycaemic Index
Diabetes is a widely researched and increasing illness around the world especially in western countries. People who are not insulin dependent are discovering that by altering their dietary intake they are better able to manage their blood sugar levels. Altering diet reduces symptoms such as excessive thirst, frequent urination, low energy, circulatory problems, and excess weight and for some a reduction in blood pressure. Food provides fuel for our body in the form of fat, protein and carbohydrates. Carbohydrates are the body's preferred fuel source. The glycaemic index (GI) is a way to rate carbohydrates according to how quickly they are absorbed and raise the glucose level of the blood. It has replaced classifying carbohydrates as either 'simple' or 'complex'.
Our Body's Attempt to Restore Balance
Insulin is a protein hormone that is released by the body to help regulate glucose metabolism from the carbohydrates, fats and proteins we consume. The majority of glucose is converted to metabolic energy, but sometimes it may be stored as fat. A diet high in refined carbohydrates (high GI) is linked to the development of insulin resistance, obesity and diabetes. The increase in glucose decreases insulin activity and receptor numbers causing a blood sugar imbalance, and has also shown to increase plasma levels of triglycerides (fats). Therefore, too much storage of fat transpires into weight gain and this becomes the link for weight management! Insulin is released in response to rapidly rising blood glucose levels from refined carbohydrates such as white sugar, white breads and cakes. Meals consisting of whole foods and complex carbohydrates such as vegetables and grains support strong insulin activity. Tender Loving Cuisine (TLC Meals) are approved as suitable for people with diabetes and also for weight control management by the Australian Diabetes Council. A complete nutritional analysis is available on their website www.tlc.org.au or by contacting their friendly staff on Freecall 1800 801 200.
Digesting and Absorbing Carbohydrates
The digestive system breaks down carbohydrate-containing foods into simple sugars, mainly glucose. For example, both baked beans and soft drink will be broken down to simple sugars in your digestive system. This simple sugar is then carried to each cell via the bloodstream. The pancreas secretes the hormone insulin, which helps the glucose to migrate from the blood into the cells. Once inside a cell, the glucose is 'burned' along with oxygen to produce energy. Our muscles, brain and nervous system all rely on glucose as their main fuel to make energy. The body converts excess glucose from food into another form called glycogen. This is stored inside muscle tissue and the liver, ready to supplement blood sugar levels should they drop between meals or during physical activity.
The Glycaemic Index
Carbohydrate-containing foods can be rated on a scale called the glycaemic index (GI). This scale ranks carbohydrate-containing foods based on their effect on blood sugar levels over a period of time - usually two hours. The GI compares carbohydrate-containing foods gram-for-gram of carbohydrate. Carbohydrate-containing foods are compared with glucose (although sometimes white bread can be used as reference food), which is given a GI score of 100. Carbohydrates that break down quickly during digestion have the highest glycaemic indexes (GI more than 70). These high GI carbohydrates give a "quick hit". The blood glucose response is fast and high. Carbohydrates that break down slowly release glucose gradually into the bloodstream. They have low glycaemic indexes (GI less than 55). The blood glucose response is slower and flatter, sustaining energy release in the body over a longer period of time helping us to feel healthier and more alert.
Choosing Between High and Low GI Foods
Which carbohydrate foods are best to eat? That depends on the situation. For example, the rate at which porridge and cornflakes are broken down to glucose is different. People with type 2 diabetes or impaired glucose tolerance, have become resistant to the action of insulin or cannot produce insulin rapidly enough to match the release of glucose into the blood after eating carbohydrate containing foods. This means their blood glucose levels may rise above the normal level. Porridge is digested to simple sugars much slower than cornflakes so the body has a chance to respond with production of insulin and the rise in blood glucose levels is less. For this reason, porridge is a better choice of breakfast cereal than cornflakes for people with type 2 diabetes. It will also provide more sustained energy for other people as well.
How Much You Eat is also Important
The amount of the carbohydrate-containing food you eat will also affect your blood glucose levels. For example, even though pasta has a low GI, it is not advisable for people with diabetes or impaired glucose tolerance to have a large serve. This is because the total amount of carbohydrate, and therefore the kilojoules, will be too high. The glycaemic load (GL) is a concept that builds on GI as it takes into account both the GI of the food and the amount of carbohydrate in a portion. GL is based on the idea that a high GI food consumed in small quantities would give the same effect on blood glucose levels as larger quantities of a low GI food. GL is easily calculated by multiplying the GI by the number of grams of carbohydrate in a serving of food.
High GI Foods are Influenced by Low GI Foods
Generally, eating low GI foods slows down the absorption of glucose from any high GI foods eaten at the same time. This is important, as most foods are eaten as part of a meal and this affects the GI value of foods. For example, eating cornflakes (a higher GI food) with milk (a lower GI food) will reduce the effect on blood sugar levels. If a person with diabetes experiences a 'hypo', where the blood glucose levels fall below the normal range of 3.5-8mmol/L, they need to eat carbohydrate-containing foods (preferably those with a high GI) to restore their blood sugar levels to normal quickly. For example, eating five jellybeans will help to raise blood glucose levels quickly.
Factors that affect the GI of a Food
Factors such as the size, texture, viscosity (internal friction or 'thickness') and ripeness of a food affect its GI. For instance, an unripe banana may have a GI of 30 while a ripe banana has a GI of 51. Both ripe and unripe bananas have a low GI. Fat, protein, soluble fibre, fructose (a carbohydrate found in fruit) and lactose (the carbohydrate in milk) also generally lower a food's glycaemic response. Fat and acid foods (like vinegar, lemon juice or acidic fruit) slow the rate at which the stomach empties and so slow the rate of digestion, resulting in a lower GI. Other factors present in food, such as phytates in wholegrain breads and cereals, may also delay a food's absorption and thus lower the GI. Cooking and processing can also affect the GI - food that is broken down into fine or smaller particles will be more easily absorbed and thus have a higher GI.
Tips for Healthy Eating
Some practical suggestions include:
. Use a breakfast cereal based on oats, barley and bran.
. Use grainy breads or breads with soy.
. Enjoy all types of fruit and vegetables.
. Eat plenty of salad vegetables with vinaigrette dressing.
. Eat a variety of carbohydrate-containing foods. If the main sources of carbohydrates in your diet are bread and potatoes then try lentils, legumes, pasta, basmati rice.
Note: TLC Meals provide a balanced meal of protein (meat portion), vegetables or grains (such as rice or lentils) in every serve and most meals are endorsed by Australian Diabetes Council as a healthier choice for blood glucose management.
Expert Medical Supervision
If you have a medical condition, such as diabetes, it is important to seek the advice of your doctor or specialist before making any changes to your diet.
Where to get help -
. Your doctor.
. An accredited practising dietician or nutritionist.
. Nutrition Australia www.nutritionaustralia.org .
Maria Mitzikis
Nutrition Consultant
Copyright, Maria Mitzikis, Nutrition Consultant
