The glycaemic index (GI) is a measure of the extent to which a food raises blood sugar. Generally speaking, the higher the GI, the unhealthier the food is. Lots of sugar generally means lots of insulin ” and excess of which can promote of a slew of unhealthy biochemical processes including increased fat-making and reduced fat mobilisation (and hence weight gain) within the body, and a raised risk of ‘insulin resistance’ which can ultimately lead to type 2 diabetes (see Wednesday’s post for more on this).
Some doubt the usefulness of the GI in nutritional management, but I for a long time have thought it is actually quite a graphic measure of the likely health effects a food will have. In the GI scale, glucose (pure and very fast releasing sugar) is assigned a value of 100. Very few will not understand the implications of eating wodges of French bread, wholemeal bread or fist-sized baked potatoes when they see that the GIs of these foods are about 95, 70 and 85 respectively. Most individuals will immediately recognise the wisdom in cutting back on these foods.
The potential benefits of eating a low-GI diet were tested recently by French researchers . In this study, 38 individuals were randomly assigned to eat a diet where the starch in the diet was either of a low GI or high GI nature. The individuals were not instructed to limit how much they ate. The trial lasted for just 5 weeks.
Despite the short duration of the trial, the group eating the low GI starch lost significantly more weight than the high GI starch consumers (1.1 kg on average compared to 0.3 kg). They also saw significant improvements in their cholesterol level (an average drop of almost 10 per cent) as well as the ratio of total cholesterol to ‘healthy’ HDL cholesterol. Both these changes would generally be viewed as a sign of reduced risk of cardiovascular disease. In comparison, the high GI eating group did not see these benefits.
The trial did not find that eating the lower GI diet improved the effectiveness of insulin (insulin sensitivity) compared to the higher GI diet. However, insulin sensitivity generally takes quite a while to change, and 5 weeks is probably not long enough for benefit to be seen in this particular parameter.
The authors of the study concluded that: Lowering the GI of daily meals with simple dietary recommendations results in increased weight loss and improved lipid profile and is relatively easy to implement with few constraints. These potential benefits of consuming a LGI (low glycaemic index) diet can be useful to develop practical dietetic advice.�
The results of this study mirror my own experience in practice: that it is possible to get benefits from dietary change that focuses not on the calorific value of the foods that people eat, but the form than these calories come in. Such an approach often liberates individuals from feelings of hunger and sacrifice that so often comes as part and parcel of conventional ‘diets’, and makes their new regime much more sustainable. I have seen countless individuals make what look like permanent positive shifts in their eating habits by embracing this sort of approach. On the other hand, I’ve know very few who have managed to ‘last’ on a diet that explicitly restricts food in terms of calorie content and therefore leaves them hungry. Quality, not quantity, is the key.
1. de Rougemont A, et al. Beneficial effects of a 5-week low-glycaemic index regimen on weight control and cardiovascular risk factors in overweight non-diabetic subjects. British Journal of Nutrition 2007;98(06):1288-1298