GI (glycaemic index) refers to how rapidly a food is converted to glucose. We all use glucose for fuel, which is made in the liver from sugars and starches (carbohydrates) that we eat. Food with a high GI index is converted rapidly, whilst food with a low GI is converted more slowly.
The relevance of this is that we use insulin to transport the glucose around our bloodstream. If glucose is produced slowly and steadily (low GI food) the insulin works effectively as a glucose ‘taxi’, taking the glucose where it’s required in the body.
However, too much glucose is toxic to the body, and so if too much is released at one time (high GI food), the body panics and more insulin is released. The insulin then transfers the glucose to fat stores, rather than the bloodstream, where it can do no harm. This can lead to weight gain, and also cause the insulin to become unresponsive and not work as an effective taxi for glucose around the body. This can also increase the risk of Type II diabetes.
In plain words: High GI foods are broken down quickly, causing a peak in the blood sugar level and making the body ‘panic’ and store the glucose in fat, contributing towards weight gain.
Low GI foods take longer to digest, so you feel fuller for longer. Eating low GI foods avoids this peak and gives you energy for longer.
A food’s GI index can be ascertained by the following categories –
How much starch does it contain? Starch in raw foods takes awhile to break down, but finely milled starch (i.e. white flour) breaks down quickly.
How much fibre? More fibre is better, as it takes longer to break down
How much fat? More fat lowers the GI, as it slows down the speed at which food leaves the stomach.
How acidic is it? Acidity slows down the progress of food through your system. Higher acidity (including lactic acid in milk products) is lower GI.
Does it contain carbohydrates? Pure protein foods (i.e. meat, eggs) and pure fats (i.e. oils, butter) have no carbohydrates and are therefore low GI. Simple carbohydrates (i.e. white flour) break down easier than complex carbohydrates (i.e. coarsely milled flour) and are high GI.
High GI foods include: parsnips, baked potatoes, bagels, watermelon, cornflakes, white bread
Low GI foods include: carrots, new potatoes, porridge, granary bread, cheeses, plain (dark) chocolate
In summary: The GI index seems to have logical scientific reasoning and is easy enough to stick to. However, there are a few weird foods that are high GI, making it trickier to memorise. If you’re going to try it, you may like to use a converter table. It would be easy to take it too literally and gorge on chocolate and peanuts, which both have high fat content.
Perhaps a solution is to be aware of low GI foods, and try to eat more of them. As this tends towards whole grains and fruit and veg, it really is the basis of a healthy diet… with dark chocolate!