What are high- and low-GI foods? Which are better, if any? What is the glycaemic index? Should I worry about it?
The glycaemic index (GI) is a food’s ability to raise blood glucose (sugar) levels.

Carbohydrates are ranked on a scale from 0 to 100 according to the extent to which they raise blood glucose levels after eating. In healthy people, protein has minimal effect on blood sugar and fat little, if any.

High GI carbs are those which are rapidly digested, absorbed and metabolised and result in marked fluctuations in blood glucose levels. Carbohydrates with a low GI (55 or less) are those that produce smaller fluctuations in blood glucose and insulin levels.

Let’s look at how the glycaemic index of food affects you in two ways:

Health
At first blush, it might seem obvious that high-GI foods are unhealthy, as spikes in insulin and blood sugar are associated with heart disease and type-2 diabetes.

But actually, for overall health, the GI of dietary carbohydrates have little if any meaningful impact if your diet is ‘sensible’ and consists predominantly of whole foods and minimal highly refined junk-type foods.

While current evidence shows modest beneficial effects of a lower-GI diet compared to a higher-GI diet in terms of glycaemic control and blood lipid profile, it’s important to note that comparisons of different-GI diets often fail to take account of macronutrient and fibre content. Lower-GI foods and diets often have a ‘head start’ because they are typically higher in fibre, protein and micronutrient density.

Body Fat
It is often claimed that high-GI foods lead to an increase in hunger and therefore body fat, partly due to the stimulatory effects of insulin. But contrary to popular belief, insulin has actually been shown to suppress appetite. A classic example of the misconception around high-GI foods and appetite response is boiled potatoes, which have been shown to be highly satiating (meaning they make us feel full).

Another finding that contradicts the widely held belief that only carbs spike insulin: protein-rich beef has been shown to be as potent a stimulator of insulin as carb-heavy brown rice, even though protein raises blood glucose to a much smaller extent than carbs.

It’s also important to note that the GI response of a given food differs between individuals and can be affected by what it’s eaten with (e.g. alongside protein, dietary fat and fibrous veg). As such, worrying about the GI of one food in isolation holds little relevance in most real-world scenarios where there is more than just one ingredient on your plate.

Studies have consistently reported that once confounding variables (e.g. fibre, energy density and macronutrient content) are controlled, neither dietary carbohydrate nor GI has an effect on body composition and on overall energy intake.

Take-home message:
For fat loss, eat in a way that leads to the greatest adherence towards an appropriate energy deficit over time. Poring over GI indices is, frankly, a poor use of time and energy! Instead, create a diet with ample protein, fibre and one that is rich in micronutrient density.

For overall health, think more about the nutritional quality of a given food rather than worrying about its rank on the GI scale. A variety of nutrient-dense foods is considered ‘the spice of life’.

Kevin Garde
Nutritionist and Bodyscan Consultant