What do we really know about the links between the glycemic index and health?

This article was written in partnership with the health channel of the University of Paris, Pour une bonne santé (PuMS).

Among the panoply of diets that bloom with the return of spring, there is one which has had some success for a few years now: the “GI” diet, two letters designating the glycemic index.

Substituting in the 1980s the erroneous (and still overused) distinction between fast sugar and slow sugar, the concept of the glycemic index was developed by two specialists in nutritional sciences, David Jenkins and Tom Wolever. It is intended to measure the impact of a food on glycemia (the level of sugar in the blood) and, therefore, on various diseases.

The mainstream press has since picked up on the concept. But can we really lose weight, prevent the onset of diabetes, limit the risk of cardiovascular accident or even cancer by playing on the glycemic index? The scientific literature is rather divided.

From index to glycemic load

The glycemic index represents the ability of a food to increase blood sugar levels within 2 hours of ingestion.

This development is not dependent on the amount of carbohydrates, in other words carbohydrates (“sugars”). Take the example of an apple and a banana, with an equivalent amount of sugars. Following the ingestion of the first, whose glycemic index is low, the blood sugar rises little and quickly returns to its initial value. On the other hand, the second, whose glycemic index is high, causes a greater increase in blood sugar, with a real peak, which also lasts longer.

The glycemic index of a food is defined by comparison with a reference food whose GI value is set at 100: if we choose white bread as a reference, for example, a food whose glycemic index is of 50 has a hyperglycemic power two times less.

Finally, the concept of glycemic index has been added that of glycemic load, in order to take into account the carbohydrate content of foods: some indeed have a high glycemic index, but containing few carbohydrates, they ultimately have little. impact on blood sugar – unless they are actually consumed in excess.

Good for losing weight?

Several interventional studies have examined the effects of diets incorporating the concepts of glycemic index and load on weight loss.

Some research has noted a benefit, with weight loss 3 to 4 kg greater than that of a diet targeting a reduction in energy intake, portions or fat. Two studies conducted in diabetic patients also revealed a slight decrease in abdominal overweight.

These results are however singular. Indeed, most other studies have not found an association, and a negative link has even been described between glycemic index and body mass index – a quantity used to assess a person’s build.

Read more: The body mass index, a good tool to know if your weight is healthy?

In summary, these contradictory data do not allow us to say that a diet with a low index or glycemic load is particularly effective for losing weight.

Another finding could explain it: contrary to popular belief, the glycemic index does not seem to have an influence on feelings of hunger or satiety, which was confirmed by a Cochrane review published in 2017.

In fact, foods with a low GI trigger a weaker response when it comes to insulin – this hormone produced by the pancreas and whose role is to regulate our blood sugar. But the level of ghrelin – the hunger hormone – is unchanged. So that on average, the daily energy intake is not changed during a low glycemic index diet.

Good for preventing the onset of diabetes?

Several observational studies show a positive association between a low GI diet and the risk of developing type 2 diabetes.

Note, however, that it is difficult to attribute these results to the GI itself rather than consuming a diet higher in fiber, or poorer in carbohydrates. And in practice, it is probably the combination of these three parameters that proves most effective.

Good for the heart and blood vessels?

Most observational studies do not find any links between on the one hand cardiovascular risk factors, namely hypercholesterolemia and high blood pressure, and on the other hand the adoption of a low glycemic index diet. .

However, possible beneficial effects have been suggested on blood lipid levels, but these supposed effects were very limited.

Finally, no association has been described between a low glycemic index diet and the occurrence of vascular, cardiac or cerebral accidents – as noted in the 2017 Cochrane review already mentioned.

Good for cancer prevention?

Several studies have shown that a high glycemic index diet is associated with a slight increased risk of colorectal cancer.

Here again, it is undoubtedly in part the presence of fiber, rather than the low glycemic index of foods, which, conversely, would be protective. Indeed, if there is one piece of data accepted by consensus, it is the interest of a diet rich in fiber to prevent digestive cancers.

In addition, an increasing trend in bladder and kidney cancer has been found in the case of a diet with a high glycemic index. An increased risk of urological cancer has already been described in hyperglycemia or hyperinsulinemia, such as diabetes or metabolic syndrome.

Two mechanisms have been put forward to explain this link. On the one hand, urinary tract infections favored by hyperglycemia could increase the risk of kidney cancer. On the other hand, insulin can increase the expression of growth factors (IGF-1) and induce the proliferation of cancer cells.

Finally, it should be noted that no association was found for hormonal cancers (breast, endometrium, prostate, ovary), or for cancers of the stomach, pancreas and lungs.

Diets associated with better health

If there is one lesson to be learned from the abundant scientific literature on low glycemic index diets, it is that they are associated with better health! And this, even if nothing allows for the moment to affirm that focusing its efforts on this index can make it possible to lose weight, cure or prevent diseases.

In view of all the data, offering a diet with a low glycemic index is therefore not the first of the necessary recommendations: it is not, moreover, one of the benchmarks of the National Health Nutrition Program. However, once the basic messages of this program have been understood and integrated, taking into account the glycemic index of foods can be useful.

Such an approach indeed leads to consuming more fiber, but also to reducing the proportion of refined foods on one’s plate. However, it is not impossible that we can thus prevent the appearance of certain cancers. However, given the complexity of the low glycemic index diet, it should rather be proposed as an additional goal to achieve, for informed people who wish to deepen their knowledge in nutrition.