Thread: Carbohydrates and the Glycemic Index

Carbohydrates and the Glycemic Index


Carbohydrates are the body's preferred fuel source. Once, nutritionists classified carbohydrates as either 'simple' or 'complex', depending on their chemical configuration of carbon, hydrogen and oxygen atoms, and the presence of fibre. All the lay person needed to know was that simple carbohydrates were the sugars and complex carbohydrates were the starches. It was recommended that we limit our intake of simple carbohydrates and get most of our fuel requirements from the starches, such as pasta, rice, bread and potatoes. Paying strict attention to simple and complex carbohydrate intakes was particularly important for those with diabetes. However, current research indicates that these old theories are inadequate. Foods are now rated on a scale called the glycaemic index, or GI.
Digestion and absorption of carbohydrates
The digestive system breaks down carbohydrates into simple sugars, predominantly glucose. This simple sugar is then transported to each cell via the bloodstream. A gland of the endocrine system, called 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. The body converts any excess of glucose into another form called 'glycogen'. Glycogen is then stored inside muscle tissue and the liver, ready to supplement blood sugar levels should they drop between meals or during physical activity.

Diabetes and glucose
People with diabetes either don't produce enough insulin (Type I diabetes) or their insulin is ineffective (Type II diabetes), which means the amount of glucose in their bloodstream (their blood sugar levels) remain too high. Symptoms include weight loss, abnormally high levels of sugar in the urine and an unquenchable thirst. It is important for people with diabetes to carefully monitor their diet to ensure a slow, steady absorption of glucose. All people with Type I diabetes and some people with Type II diabetes need to inject themselves with insulin to make sure that their blood sugar levels are adequately controlled. For most people who suffer from Type II diabetes, exercise and weight loss can improve sensitivity and response to the body's insulin.

'Simple' versus 'complex' carbohydrates
It was once recommended that people with diabetes should limit their carbohydrate intake to complex carbohydrates, because it was believed that the glucose was released much more slowly from the gut into the bloodstream. On the other hand, simple carbohydrates were thought be absorbed rapidly, giving the body a glucose 'hit' and provoking a more severe response from the pancreas. In fact, it turns out that many simple carbohydrates are absorbed much more slowly than complex ones. Several carbohydrate-rich foods, which mainly contain sugars (for example, fruit and flavoured yoghurt), produce less of a glucose 'hit', or glycaemic response, when eaten than foods high in 'complex' carbohydrates like bread and potatoes.

The glycaemic index
The terms 'simple' and 'complex' for classifying carbohydrates are becoming obsolete. The glycaemic index - GI - is a newer and more commonly used method to rate carbohydrates. The GI measures the rise in blood sugar levels caused by a measured quantity of a particular food. Foods are given a score out of 100, where white bread (GI of 70) is used as a reference food and all foods are compared to it. Those which take longer to be absorbed are called 'low GI' (GI less than 55). Carbohydrates which offer a quick hit are called 'high GI' (GI greater than 70). It is recommended that all people, and especially people with diabetes, choose to eat low GI foods most of the time. Some studies have shown that diets leaning towards low GI carbohydrates can:

Lower blood cholesterol levels
Lower the risks of heart disease and diabetes
Help with weight loss and weight maintenance, as the slow absorption of glucose may help to sustain a feeling of fullness.

High GI foods are influenced by low GI foods
The absorption of glucose from the small intestine into the bloodstream is influenced by other foods eaten at the same time. Generally, eating low GI foods slows down the absorption of glucose from any high GI foods eaten along with them. This is important as most foods are not eaten singularly but as a meal and this affects the GI value of foods.

People with Type II diabetes benefit from consuming a diet that contains predominantly low GI foods. It is recommended that they consume at least one low GI food at each meal. A little sugar (equivalent of 2 tablespoons or 50g over a day) added to otherwise healthy and lower GI foods, such as spreading honey on wholegrain bread, is generally acceptable and will not adversely affect blood sugar levels.

Foods with a high glycaemic index can help to manage blood glucose levels, especially when blood glucose falls below normal levels. High glycaemic foods can quickly deliver glucose to the blood stream to restore blood glucose to normal levels.

GI scale examples
Some examples of the GI rating of various carbohydrates include:
Low GI (less than 55) - soy products, beans, fruit, milk, grainy bread
Medium GI (55 to 70) - sugar, orange juice and oats
High GI (greater than 70) - potatoes, wholemeal and white bread, and rice.

Factors which affect the glycaemic index of a food
Factors such as the size, texture, viscosity and ripeness of a food affect its glycaemic index. For instance, an unripe banana may have a glycaemic index of 30 but a ripe banana may have a glycaemic index of 52. The presence of fat, protein, soluble fibre, fructose (a carbohydrate found in fruit), and lactose (the carbohydrate in milk) also generally lowers a food's glycaemic response. Other factors present in food, such as phytates in wholegrain breads and cereals, may also delay a food's absorption and thus lower its glycaemic index.

The presence of dietary fibre does not always seem to delay absorption, as blood glucose responses to wholemeal bread are similar to those following the consumption of white bread.

Better Health Channel

Old thread, but yea I was checking it out and brown rice is med GI and high GL. I eat brown rice as my main carb for the day, like in 4 meals...

Is it still as good as we though?