Carbohydrates

While the media frenzy regarding high protein/low carbohydrate diets continues, one major factor is constantly ignored. Not all carbohydrates are equal and they do not all affect your body in the same way. Foods containing carbohydrate cannot be simply lumped together and denounced as bad for us based on the fact that they raise our blood glucose and insulin levels. Over the last 20 years researchers have been measuring actual blood glucose responses to foods and the results have shaken up all the traditional views on carbohydrates.

The GI (Glycemic Index) has shown us that the assumption that sugars have a bigger immediate impact on your blood sugars than complex carbohydrates is incorrect and outdated. For example white bread will cause a larger and more rapid rise in your blood glucose than the same amount of carbohydrate sugar in a fruit juice drink or even the same amount of table sugar. The GI provides a key to assessing the quality of the carbohydrate-rich foods you eat and ranks foods according to their measured effect on blood glucose levels when compared gram for gram of carbohydrate. While research in this area will continue for years to come, it is already clear that following a high-GI diet is detrimental to both health and weight control, while following a low-GI diet reduces your risk of heart disease, diabetes and can help you to lose body fat.

In short a high GI food such as potatoes is broken down and absorbed quickly, producing a large and rapid rise in your blood glucose levels (shown above). This in turn forces your body to produce a correspondingly large amount of the hormone insulin. Insulin’s job is to take the glucose, as well as incoming fat and protein from the meal, out of the blood and into the cells where they are needed. Meanwhile insulin also instructs fat cells to stop releasing stored fat into the bloodstream to use as fuel and store what is coming in. This is all a normal part of metabolism. Indeed without insulin we would not be able to survive.

The problem comes when there is too much insulin around too much of the time. Such a situation makes it hard for the body to burn fat effectively and slowly over time a net gain in body fat occurs. In addition the more rapid fall in blood glucose (there is sometimes a dip 1.5 to two hours after a meal) stimulates us to eat again. Many studies have now shown that low GI foods are more filling and keep you full for longer thereby helping you to eat less. Many nutrition scientists also believe that the combination of the predominance of high GI foods in our diet (something that has occurred only in the last 50 or so years) and these two insulin mechanisms are contributing to people becoming overweight and obese.

Our bodies are designed to run on carbohydrate - glucose must be kept at a certain level in the bloodstream for our bodies to function. The key therefore is to provide our body with a slow steady stream of incoming carbohydrate, avoiding large rapid influxes which overload the system. Low GI foods in appropriate quantities for your body meet this need. Low GI foods are usually those that are less processed and refined – in other words they are closer to their natural state. They include many wholegrains, such as barley, oats, legumes (beans and lentils), buckwheat and quinoa, and wholegrain products such as wholegrain bread and All Bran. Many other foods also have a low GI because they have characteristics which slow digestion and absorption eg pasta, noodles, dairy products, fruit and basmati rice.

Quick GI ready-reckoner

1 Quinoa is a tiny South American grain. It is rich in nutrients as well as having a low GI. It has a subtle, delicate flavour and is therefore good as an accompaniment to flavoursome stews, curries and casseroles in place of rice or couscous.