What is the Glycemic Index and Why Should You Care?

You may have heard a lot about GI or glycemic index recently.  Many well known food products use ‘low GI’ as a marketing message, promising ‘long lasting energy’.   Other products simply boast the small GI symbol on their packaging.  There is a GI diet, and many recipe books and magazines feature recipes that are low GI.  But what exactly is GI and is a diet based on low GI foods beneficial for our health?

What is GI?

GI or glycemic index is a rating system from 0 to 100, based on the effect that a food has on blood sugar levels when it is eaten. Only foods containing carbohydrates can have a GI rating, as carbohydrates are broken during digestion to their simplest form, sugars.   High GI foods with ratings of 70 or more are those which are digested and absorbed quickly, causing a rapid increase in blood sugar, usually followed by a substantial drop in levels.  Low GI foods, with a rating less than 55 on the other hand, are absorbed and digested more slowly and therefore cause a more gradual rise in blood sugar levels that is maintained over a longer time frame.

Why is GI important?

The GI of the food you eat is important for everyone.  Quick rises in blood glucose levels, such as those produced by high GI foods, can cause us to feel hungry again soon after eating.  This is due to the rapid drop of the blood sugar after the initial peak.  Low GI foods however, can keep you full for longer, as your blood sugar is maintained at a constant level over an extended period of time.

Maintaining blood sugar levels at a constant level is particularly important for people with Diabetes.  Type 2 Diabetics do not respond to insulin, a hormone in the body that regulates blood sugar levels by allowing the uptake of sugar into the cells for energy.  If people with diabetes experience large increases in blood sugar levels, over time, this can do extensive damage to the body.

GI is also important when doing sport.  Athletes need to eat the correct foods for training and competing to ensure their blood sugar levels stay constant.  Exercise increases insulin production, so if a person does a lot of exercise their blood sugar levels can drop very low.  An athlete may need to eat high GI foods before competing or during a race to boost depleted levels of blood sugar quickly.

What are the benefits of a low GI diet?

A low GI diet has proven benefits for health. A diet based on low GI foods can be beneficial for weight control, due to delayed hunger and appetite control produced by stabilized blood sugar levels.  This means that you eat less overall, contributing to weight loss or control, and are less likely to crave high sugar and calorie foods.

Insulin resistance is also reduced with a low GI diet.  When the body is constantly producing insulin to facilitate the uptake of glucose into the cells of the body and reduce the blood glucose levels, eventually the body can become resistant to this insulin.  This means that blood sugar levels stay high, which can do damage to blood vessels and organs in the body.  This is how type 2 Diabetes usually develops.

The Harvard School of Public Health has performed studies that suggest that the risk of lifestyle diseases such as Type 2 Diabetes and heart disease are related to the overall GI of a person’s diet, and that a lower GI diet reduces risk of these conditions.  The World Health Organisation (WHO), recommends that people living in industrialised countries should follow a low GI diet to reduce risk of these common diseases.

What are some low GI food options?

So we know a low GI diet can have health benefits, but what foods should we actually be eating?  Choosing healthy low GI options can be more difficult that it seems.  Whilst fresh foods are easy to identify as low or high GI, composite foods made up of multiple ingredients can be more difficult.  Unfortunately, foods with a high fat content usually have a low GI.  This is because fat slows gastric emptying and therefore increases digestion time.  Ice cream and chocolate are both relatively low GI foods, but are obviously not healthy choices and are likely to contribute to weight gain. See also how to read a nutrition label 

Combinations of foods in a meal can also affect blood sugar levels.  If a high GI and low GI food are eaten together for example, the effect will be a moderate rise in blood sugar levels.  An example of this is eating a potato with baked beans, the potato is high GI, but the beans are low, so the effect on blood sugars is moderated.

For optimum results it is best to eat low GI foods the majority of the time, however, if the occasion arises where this is not possible, try to at least combine high GI choices with lower GI options to reduce the effect on your blood sugars. See also: What are the healthiest foods to lose weight

Easy low GI food swaps

Cereals

Swap puffed rice cereals (GI 82), cornflakes  (GI 80)and puffed wheat  (GI 80) for porridge (GI 58), natural muesli  (GI 40) or All-Bran (GI 50)

Bread

Swap white bread (GI 71), baguettes (GI 98) and bagels (GI 72) for wholewheat(GI 49), soya and linseed  (GI 36)or sourdough (GI 54).

Swap taco shells (GI 68) for wheat tortilla (GI 30)

Fruit

Swap dates (GI 103) for prunes (GI 30)

Swap watermelon (GI 80) for apples (GI 34)

Vegetables

Swap potatoes (GI 60) for sweet potatoes (GI 48)

Swap pumpkin (GI 75) for carrots (GI 41)

Most vegetables are quite low in carbohydrates and have a low GI

Snack foods

Swap pretzels (GI 83) for nuts (GI 13-25)

Swap water crackers (GI 78) and rice cakes  (GI 87)for oatmeal crackers (GI 55)

Swap maple flavoured syrup (GI 68) for  jam (GI 51) or Nutella (GI 33)

Swap scones (GI 92) and donuts  (GI 76) for a nut and seed muesli bar (GI 49).

Pasta and rice

Swap short grain rice (GI 83) for long grain (GI 50) or brown rice (GI 50)

Swap rice noodles for wheat pasta (GI 54) or instant noodles (GI 47)

Dairy

All dairy products are low GI with the exception of ice cream which is classified as medium (GI 62)

Legumes

All legumes are low GI.

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