Glycaemic Index and Carbohydrates

The glycaemic index (GI) measures carbohydrates according to how quickly they are absorbed and raise the glucose level of the blood. A low GI diet may help weight loss and may also help energy levels for endurance sports.

Download the PDF version of this fact sheetEmail this fact sheet

Food and drinks provide fuel for our body in the form of fat, protein, carbohydrates and alcohol. 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’.

Foods that contain carbohydrates include bread, breakfast cereals, rice, pasta, legumes, corn, potato, fruit, milk, yoghurt, sugar, biscuits, cakes and lollies.

Digesting and absorbing carbohydrates

The digestive system breaks down carbohydrate-containing foods into simple sugars, mainly glucose. For example, both rice and soft drink will be broken down to simple sugars in your digestive system. This simple sugar is then carried to each cell through the bloodstream.

The pancreas secretes a hormone called 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 if 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 foods that have gram-for-gram the same amount of carbohydrate.

Carbohydrate-containing foods are compared with glucose (although sometimes white bread can be used as a 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 release their glucose into the blood quickly.

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.

Choosing between high and low GI foods

The best carbohydrate food to eat varies depending 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 more slowly 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.

GI and weight loss

A low GI diet is commonly promoted as an effective way to help lose weight by controlling blood sugars and appetite. When high and low GI diets are compared head-to-head, however, scientific evidence has shown that there is no additional benefit for weight loss of a low GI diet over a similar diet of nutrient composition that is high GI.

While GI can be a useful guide in planning a diet, it should not be the only consideration. Both the serving size of foods and the nutritional quality of the diet are just as important to consider.

GI and exercise

Eating low GI foods two hours before endurance events, such as long-distance running, may improve exercise capacity. It is thought that the meal will have left your stomach before you start the event, but remains in your small intestine releasing energy for a few hours afterwards. On the other hand, high GI foods are recommended during the first 24 hours of recovery after an event to rapidly replenish muscle fuel stores (glycogen).

High GI foods are influenced by low GI foods

Generally, eating low GI foods and high GI foods at the same time has the effect of ‘averaging’ the GI. 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.

GI scale examples

Some examples of the GI rating of various carbohydrates include:

  • Low GI (less than 55) – soy products, beans, fruit, milk, pasta, grainy bread, porridge and lentils.
  • Medium GI (55 to 70) – orange juice, basmati rice and wholemeal bread.
  • High GI (greater than 70) – potatoes, white bread and long-grain rice (other than basmati).

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 so has a higher GI. Foods that have been cooked and allowed to cool (potatoes, for example) can have a lower GI when eaten cold than when cooked.

GI symbol on packaged foods

A food-packaging symbol for comparing the effect of different foods on blood sugar was launched in Australia in July 2002. The GI symbol, G – Glycemic index tested, indicates the GI rating of packaged food products in supermarkets. It ranks food products based on the speed at which they break down from carbohydrate to sugar in the bloodstream.

The GI symbol only appears on food products that meet certain nutrient criteria for that food category. High and intermediate GI soft drinks, cordials, syrups, confectionery and sugars are excluded. Jams, honey and other carbohydrate-containing spreads are not necessarily excluded.

Using the GI as a guide to healthy eating

The GI can be used as a guide to healthy eating, as long as you are aware of the limitations. For example, the GI of some fruits, vegetables and cereals can be higher than foods that are considered to be treats, such as biscuits and cakes. This does not mean we should replace fruit, vegetables and cereals with treats, because the first are rich in important nutrients and antioxidants and the treats are not. GI can be a useful concept in making good food substitution choices, such as having oats instead of cornflakes, or eating grainy bread instead of white bread.

It is not always possible or necessary to choose all low GI foods. There is room in a healthy diet for moderate to high GI foods and many of these foods can provide important sources of nutrients. If you mix a low GI food with a high GI food, you will get an intermediate GI for that meal.

Tips for healthy eating

Some practical suggestions include:

  • Use a breakfast cereal based on oats, barley or 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 and pita breads.
  • Focus more on the serving size of foods, rather than just their GI rating.

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
  • Dietitians Association of Australia Tel. 1800 812 942
  • Nutrition Australia.

Things to remember

  • The glycaemic index (GI) rates carbohydrates according to how quickly they raise the glucose level of the blood.
  • The glycaemic load (GL) rates carbohydrates according to the glycaemic index and the amount of carbohydrate in the food.
  • A low GI rating of a food does not mean you can eat a larger serve of that food – the total amount of carbohydrate and kilojoules consumed are still important.
  • Choose a diet containing plenty of fruits, vegetables and legumes, but with smaller helpings of potatoes and less highly refined grain products and concentrated sugar.
Advertisements

Pure White and Deadly

Of all the foods consumed today, refined sugar is considered to be one of the most harmful.

…In 1997 Americans devoured 7.3 billion pounds of candy. Americans spent an estimated $23.1 billion dollars on candy and gum. The average American consumed a record 27.3 pounds of candy and gum in the same year-the equivalent of about six regular sized chocolate bars a week-marking the fifth consecutive year of increased demand.(1)

…Consumption of processed foods (which are laced with sugar) cost the American public more than $54 billion in dental bills each year, so the dental industry reaps huge profits from the programmed addiction of the public to sugar products.

…Today we have a nation that is addicted to sugar. In 1915, the national average of sugar consumption (per year) was around 15 to 20 pounds per person. Today the average person consumes his/her weight in sugar, plus over 20 pounds of corn syrup.

To add more horrors to these facts there are some people that use no sweets and some who use much less than the average figure, which means that there is a percentage of the population that consume a great deal more refined sugar than their body weight. The human body cannot tolerate this large amount of refined carbohydrates. The vital organs in the body are actually damaged by this gross intake of sugar.

…Refined sugar contains no fiber, no minerals, no proteins, no fats, no enzymes, only empty calories. What happens when you eat a refined carbohydrate like sugar? Your body must borrow vital nutrients from healthy cells to metabolize the incomplete food. Calcium, sodium, potassium and magnesium are taken from various parts of the body to make use of the sugar. Many times, so much calcium is used to neutralize the effects of sugar that the bones become osteoporotic due to the withdrawn calcium.

Likewise, the teeth are affected and they lose their components until decay occurs and hastens their loss.

…Refined sugar is void of all nutrients, consequently it causes the body to deplete its own stores of various vitamins, minerals and enzymes. If sugar consumption is continued, an over-acid condition results, and more minerals are needed from deep in the body to correct the imbalance. If the body is lacking the nutrients used to metabolize sugar, it will not be able to properly handle and rid itself of the poisonous residues.

These wastes accumulate through the brain and nervous system, which speeds up cellular death. The bloodstream becomes over-loaded with waste products and symptoms of carbonic poisoning result.

…Sugar also makes the blood very thick and sticky, inhibiting much of the blood flow into the minute capillaries that supply our gums and teeth with vital nutrients. Therefore, we wind up with diseased gums and starving teeth. America and England, the two largest sugar consumers, have horrendous dental problems.

…In 1948, a $57,000 ten-year study was awarded to Harvard University by the Sugar Research Foundation to find out how sugar causes cavities in teeth and how to prevent it. In 1958, Time magazine reported the findings, which were reported in the Dental Association Journal. They discovered there was no way to prevent the problem and their funding immediately disappeared.

…“The most significant human study was done in Sweden, reported in 1954, and known as the Vipeholm Dental Caries Study. More than 400 adult mental patients were placed on controlled diets and observed for five years. The subjects were divided into various groups. Some ate complex and simple carbohydrates at mealtimes only, while other supplemented mealtime food with between-meal-snacks, sweetened with sucrose, chocolate, caramel, or toffee.

Among the conclusions drawn from the study, was that sucrose consumption could increase caries activity. The risk increased if the sucrose was consumed in a sticky form that adhered to the tooth’s surfaces. The greatest damage was inflicted by foods with high concentrations of sucrose, in sticky form, eaten between meals, even if contact with the tooth’s surfaces was brief. Caries, due to the intake of foods with high sucrose levels, could be decreased when such offending foods were eliminated from the diet.

But individual differences existed, and in some cases, caries continued to appear despite avoidance of refined sugar or maximum restriction of natural sugars and total dietary carbohydrates.” (2)

…Diabetes is another commonly known disease caused by sugar as well as a high fat diet. Diabetes is caused by the failure of the pancreas to produce adequate insulin when the blood sugar rises. A concentrated amount of sugar introduced into the system sends the body into shock from the rapid rise in the blood sugar level. The pancreas eventually wears out from overwork and diabetes then rears its ugly head.

…Hypoglycemia occurs when the pancreas overreacts to the large amount of sugar in the blood and releases too much insulin leaving one with the “tired” feeling as the blood sugar level becomes lower than it should be.

“A recent article in the British Medical Journal, entitled The Sweet Road to Gallstones, reported that refined sugar may be one of the major dietary risk factors in gallstone disease. Gallstones are composed of fats and calcium. Sugar can upset all of the minerals, and one of the minerals, calcium, can become toxic or nonfunctioning, depositing itself anywhere in the body, including the gallbladder.

…“One out of ten Americans has gallstones. This risk increases to one out of every five after age forty. Gallstones may go unnoticed or may cause pain-wrenching pain. Other symptoms might include bloating, belching, and intolerance to foods.” (3)

…Another serious problem with sugar that is now coming to the forefront is the various levels of mental problems. Our brains are very sensitive and react to quick chemical changes within the body. As sugar is consumed, our cells are robbed of their B vitamin, which destroys them, and insulin production is inhibited. Low insulin production means a high sugar (glucose) level in the bloodstream, which can lead to a confused mental state or unsound mind, and has also been linked with juvenile criminal behavior.

Dr. Alexander G. Schauss, brings this solemn fact out in his book,Diet, Crime and Delinquency. Many mental ward and prison inmates are “sugarholics” and erratic emotional outbreaks often follow a sugar binge.

REFINED SUGAR-A DRUG?

…Refined sugar, by some, is called a drug, because in the refining process everything of food value has been removed except the carbohydrates-pure calories, without vitamins, minerals, proteins, fats, enzymes or any of the other elements that make up food. Many nutrition experts say that white sugar is extremely harmful, possibly as harmful as a drug, especially in the quantities consumed by the present-day American.

…Dr. David Reuben, author of Everything You Always Wanted to Know About Nutrition says, “…white refined sugar-is not a food. It is a pure chemical extracted from plant sources, purer in fact than cocaine, which it resembles in many ways. Its true name is sucrose and its chemical formula is C12H22O11.

 

It has 12 carbon atoms, 22 hydrogen atoms, 11 oxygen atoms, and absolutely nothing else to offer.” …The chemical formula for cocaine is C17H21NO4. Sugar’s formula again is C12H22O11. For all practical purposes, the difference is that sugar is missing the “N”, or nitrogen atom. …Refining means to make “pure” by a process of extraction or separation. Sugars are refined by taking a natural food, which contains a high percentage of sugar, and then removing all elements of that food until only the sugar remains. …While sugar is commonly made from sugar cane or sugar beets.

Through heating and mechanical and chemical processing, all vitamins, minerals, proteins, fats, enzymes and indeed every nutrient is removed until only the sugar remains. Sugar cane and sugar beets are first harvested and then chopped into small pieces, squeezing out the juice, which is then mixed with water. This liquid is then heated, and lime is added.

Moisture is boiled away, and the remaining fluid is pumped into vacuum pans to concentrate the juice. By this time, the liquid is starting to crystallize, and is ready to be placed into a centrifuge machine where any remaining residues (like molasses) are spun away. The crystals are then dissolved by heating to the boiling point and passed through charcoal filters.

After the crystals condense, they are bleached snow-white usually by the use of pork or cattle bones. …During the refining process, 64 food elements are destroyed. All the potassium, magnesium, calcium, iron, manganese, phosphate, and sulfate are removed. The A, D, and B, vitamins are destroyed.

Amino acids, vital enzymes, unsaturated fats, and all fiber are gone. To a lesser or greater degree, all refined sweeteners such as corn syrup, maple syrup, etc., undergo similar destructive processes. Molasses is the chemical and deranged nutrients that is a byproduct of sugar manufacture.

…Sugar manufacturers are aggressive in defending their product and have a strong political lobby which allows them to continue selling a deadly food item that by all reason should not be allowed in the American diet.

…If you have any doubts as to the detriments of sugar (sucrose), try leaving it out of your diet for several weeks and see if it makes a difference! You may also notice you have acquired an addiction and experience some withdrawal symptoms.

…Studies show that “sugar” is just as habit-forming as any narcotic; and its use, misuse, and abuse is our nation’s number one disaster.

It is no wonder when we consider all the products we consume daily which are loaded with sugar! The average healthy digestive system can digest and eliminate from two to four teaspoons of sugar daily, usually without noticeable problems, (that is if damage is not already present).

One 12 oz. Cola contains 11 teaspoons of sugar, and that’s aside from the caffeine. It’s the sugar that gives you quick energy, but only for a brief time due to the rise of the blood sugar level. But the body quickly releases a rush of insulin, which rapidly lowers the blood sugar and causes a significant drop in energy and endurance. It is easy to see why America’s health is in serious trouble.

— top^

EFFECT OF SUGAR ON NEUROLOGICAL PROCESSES …One of the keys to orderly brain function is glutamic acid, and this compound is found in many vegetables. When sugar is consumed, the bacteria in the intestines, which manufacture B vitamin complexes, begin to die-these bacteria normally thrive in a symbiotic relationship with the human body. When the B vitamin complex level declines, the glutamic acid (normally transformed into “go” “no-go” directive neural enzymes by the B vitamins) is not processed and sleepiness occurs, as well as a decreased ability for short-term memory function and numerical calculative abilities. The removal of B vitamins when foods are “processed” makes the situation even more tenuous.

 

WHAT ABOUT GUM CHEWING? …Besides the sugar in gum being damaging to the teeth there is another harmful problem to consider and that is: “teeth and jaws weren’t designed for more than a few minutes of solid chewing per day-far less than the two hours clocked in daily by hardcore gum chewers. All this chewing results in inordinate wear on the jawbone, gum tissue and lower molars, and can change the alignment of the jaws” says Michael Elsohn, D.D.S., in the Medical Tribune.

— top^

ENDNOTES:– top^ (1) U.S. Commerce Department figures compiled for the National Confectioners Association (NCA) and the Chocolate Manufacturers Association. (Reuters, 8/21/98) (2) Beatrice Trum Humter, The Sugar Trap & How to Avoid It, (Houghton Mifflin Co., 1982), p.15. (3) Nancy Appleton, Ph.D., Lick The Sugar Habit, (Warner Books, N.Y., 1985) pp. 73,74.