The Glycaemic Index

In the May issue of IOH, I discussed ‘fad diets’. I don’t know if you noticed but I didn’t include the Glycaemic Index (GI) diet. The reason being is that I don’t think of it as a ‘fad’. For some reason the GI diet seemed to only get popular in recent years, possibly when celebrities started following it. Books were then published about it and foods were marketed and sold as low GI. Although new to the public, the concept of GI was developed by researchers in 1980 and has been used by dietitians in nutrition education over the past 2 decades.

What is the GI diet?  The GI is a ranking of carbohydrate (starchy) foods based on the rate at which they raise blood glucose (sugar) levels.  Foods that break down quickly will raise blood glucose quickly and are given high GI values. Similarly, foods that break down slowly will raise blood glucose slowly, and are given low GI values. The GI of pure glucose is set at 100 and every other food is ranked on a scale from 0 to 100 according to its actual effect on blood glucose levels.

• Low GI foods fall below 55
• Intermediate GI foods between 55 and 70; and
• High GI foods above 70

The table below shows examples of Low GI, Moderate GI and High GI foods:

Once food has been broken down (digested) in the intestines, the glucose goes into the blood and then into the various body tissues, i.e. muscles, where it is used for energy. When you eat low GI foods, your body takes longer to digest and absorb the carbohydrate, which will help keep your blood glucose levels steady between meals. The level of glucose in the blood is higher after meals and is usually at its lowest first thing in the morning before you have breakfast.

So, what’s the hype? Slow, steady rises and falls in glucose will help you feel full for longer therefore controlling appetite and aiding in weight loss. It has also been found to decrease the risk of developing Type 2 diabetes and heart disease.

There are however, a number of factors which will influence GI. Fats and protein lower the GI i.e. chocolate has a low GI; genetic variety i.e. basmati rice has a lower GI than white; the degree of ripeness i.e. unripe banana has a lower GI; and method of cooking i.e. fried potatoes have a lower GI than baked potatoes.  Also, when you mix foods together, the GI changes. So, a high GI food (like a jacket potato) when mixed with a low GI food (like baked beans) becomes a medium GI meal. If you add a salad or vegetables to you meal, it will help to lower the overall GI.

The problem is no one ever eats foods in isolation. If you were to confine yourself to low GI foods, your diet would be unbalanced and high in fat, which could lead to weight gain and increase your risk of heart disease.   For this reason it is important not to focus exclusively on GI. The amount of carbohydrate eaten at a meal also needs to be considered. A large helping of a low GI food will still have a greater effect than a small amount of a high GI food. For this reason the Glycaemic load (GL) of a meal was developed, which in my opinion is a more meaningful guide to assess the amount of glucose / sugar in the blood. The GL is a measure of the total response to a food or meal, calculated with the GI figure and the amount of carbohydrate in a serving – it relates to what we actually eat (whereas GI doesn’t) and will give a more accurate prediction of how foods will affect your blood sugar levels. So, the small amount of carbohydrate in a typical portion in some high GI foods, such as carrots or watermelon, gives them a low GL figure.

Working with GL is very interesting. In my experience clients can usually ‘feel’ the difference by following a low GL diet. By balancing blood sugar levels, you will not experience afternoon energy slumps or sugar cravings which are caused by eating high GL foods which raise your blood sugar levels very quickly, then plummet causing the energy slumps and cravings for more high GL sugary foods, creating a vicious and unhealthy cycle of blood sugar highs and lows.

I know what you thinking – this is confusing!  But, it’s not as difficult as you think.  Most low GI foods e.g. wholegrain breads, pasta, fruit, vegetables, beans and lentils are generally inherently healthy. Basing a diet plan on low GI foods of this kind – with keeping your portion sizes in check too – can help you keep to healthy eating guidelines.

I have put together a low GL diet plan to give you an idea of how easy it is:

Breakfast

• 1- 1 ½ cups of oat/ bran based breakfast cereal (Porridge, All Bran Flakes) with semi skimmed milk and a medium banana

Snack

·         Orange

• Low fat yogurt (125g)

Lunch

• Baked beans with medium jacket potato and salad /
• or wholemeal bread sandwich with tuna and salad
• Apple

Snack

• 1 slice of Rye bread or fruit loaf with low fat spread
• 2 Plums

Evening meal

• Chicken stir fry and vegetables
• 3 heaped tablespoons of basmati rice

Remember to also think about healthy eating guidelines and not only GI. Foods with a high GI are not necessarily “unhealthy”.  Chocolate pudding for example has a low GI because it is high in fat and watermelon has a high GI but is healthy! Here are some other tips to help you on your way:  include fruit as a snack or part of a main meal; add vegetables to main meals; try a lentil based soup; add variety with different breads, eg pita bread and bread made with a substantial amount of mixed grains and pumpernickel.

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