Once upon a time, carbohydrates were either 'simple' or 'complex'. Simple carbohydrates like honey, we thought, were quickly absorbed into the bloodstream and complex carbohydrates like bread were more slowly absorbed, because of their more complicated structure. The science was straightforward, or so it seemed.
Nowadays, the Glycaemic Index (GI) of carbohydrates debunks this theory. It gives scientists a better measure of just how high and how quickly different carbohydrates raise blood glucose levels. As a result, we are beginning to grasp the effects of certain foods on hunger and appetite control. Foods can be classified as having a low, intermediate or high glycaemic index or GI and are ranked from zero to 100.
Based on these findings, our bodies, we know, can rapidly break down and convert a fast food meal containing high GI carbohydrates such as French fries, burger buns and soft drinks into glucose. This glucose is absorbed into the blood stream and spikes the glucose level there, resulting in what the Americans call a 'sugar high'! The problem arises after the spike, when glucose quickly disappears from the bloodstream leaving us feeling sluggish and hungry again.
In effect, what happens is that the rapid spike signals the pancreas to release more insulin, a hormone which diverts the glucose from the blood and into various body tissues. Here, it is either burned immediately or stored as fat. Insulin also stops our bodies from converting this fat back into glucose for the body to burn. Bad news for the waist line.
In contrast, low GI foods give more controlled blood glucose levels and no rapid spikes. A diet based on low GI carbohydrates leaves us feeling fuller for longer, helps control appetite and keeps hunger pangs at bay. Good news for anyone trying to slim.
Small changes such as choosing pasta or a boiled potato instead of white rice are examples of how the GI of meals can be lowered.
One of the most important implications of the GI factor is in the area of diabetes. Evidence suggests that replacing high GI foods with low GI ones can help patients control and regulate their blood glucose levels. In the past, people with diabetes were advised to avoid table sugar as it was thought to raise blood glucose levels rapidly.
Current recommendations now allow a modest amount of table sugar as the inclusion of a little sugar as part of a meal has little impact on either blood sugar or insulin concentrations.
Raised eyebrows or even whoops of joy can be expected when slimmers or people with diabetes take their first glimpse at the list of low GI foods. Fantastic - chocolate is better than wholemeal bread, table sugar is better than a baked potato! Unfortunately, this is not the correct interpretation. The GI table is only classifying foods on the basis of their effect on blood glucose levels. Other factors such as how much fibre, vitamins and minerals and essential fatty acids the food contains are important.
Lowering the GI of your diet does not require the elimination of all high GI foods such as wholemeal bread, but it could signal that restraint is necessary if you tend to eat a lot of bread, yet you're always hungry. So, instead of having two or three slices of bread, you could eat one slice instead topped with baked beans to promote satiety. It also means you don't need to live in terror of a little bit of chocolate now and then when you have diabetes. Just make sure you have it with your meal.
It's essential that GI is kept in perspective and that it is remembered that all high carbohydrate foods can make an important contribution to a healthy well-balanced diet. While the World Health Organisation has endorsed the use of GI in the management of certain diseases, there isn't universal consensus on the merits of GI as yet. We still have work to do. We need to standardise the methods we use to measure GI for the correct interpretation and application of GI values in practice. Research is ongoing. Watch this space.
Next week: Foods to oil the joints and build-up bones.