As the prevalence of obesity has increased over the last couple of decades, researchers have been investigating the causes. They have observed that factors other than dietary fat intake may be responsible. Carbohydrates appear to be associated with weight gain. Traditionally, carbohydrates were classified by their chemical structure, that is, either simple (sugars) or complex carbohydrates. This method however is not related to the blood glucose (blood sugar levels) and insulin responses in the body.
More recently researchers have developed a new method of classifying carbohydrates, known as the glycaemic index (GI). The glycaemic index allows foods to be classified by their effect on blood glucose response rather than their chemical composition.
Food carbohydrates that break down rapidly during digestion have the highest GI values because the blood glucose response is high, that is the blood sugar levels rise sharply. High GI foods (GI value greater than 70) include potatoes, white rice and bread. The opposite to this are the low GI foods that break down slowly, releasing glucose gradually in the blood. Low GI foods (GI value less than 55) include pasta, legumes and porridge. It is thought that low GI foods are the most satisfying and sustaining and help reduce overeating.
Yunsheng Ma and colleagues from the University of Massachusetts investigated the association of body mass index (BMI) with dietary intake of carbohydrates. Information from 572 healthy adults aged 20 to 70 years was collected between 1994 and 1998. The data included a seven-day dietary survey, body weight (BMI) and levels of physical activity.
The researchers conclude that daily dietary GI is positively associated with BMI - people with a higher BMI tend to eat high GI carbohydrates and those who have a lower BMI tend to eat low GI carbohydrates. It is thought that those who generally eat more high GI foods produce more insulin and store more fat.
Ma and team also note that, "our data did not support the current public trend of lowering total carbohydrate intake or lowering glycaemic load for weight loss."
References available on request