The glycemic index: understanding and using this concept on a daily basis

Not all carbs are equal: what if I could choose the ones that give me lasting energy?

For decades, carbohydrates have been classified into two simple categories: fast sugars and slow sugars. This distinction, although intuitive, is scientifically inaccurate. Nutrition research has developed much more precise tools to characterize the effect of carbohydrates on glycemia - the sugar level in the blood. The glycemic index (GI) and the glycemic load (GL) are the two most important. Understanding these concepts and knowing how to use them concretely in my food choices is one of the most effective levers for preventing type 2 diabetes, stabilizing my daily energy and optimizing my metabolic health.

1. What is the glycemic index?

The glycemic index (GI) is a measurement which indicates the speed at which the carbohydrates in a food raise blood sugar (blood glucose level) after ingestion, compared to a reference food (pure glucose = GI 100 or white bread = GI 100 depending on the scales).

It is classified into three categories:

When I eat a high GI food, my blood sugar rises quickly, triggering a strong secretion of insulin to bring glucose back into the cells. This rapid drop in blood sugar then generates the feeling of hunger and the well-known slump 1 to 2 hours after the meal. With a low GI food, the glycemic rise is gradual, insulin is released moderately and energy is released over a longer period.

Category	GI Value	Examples
Bottom IG	55 or less	Legumes (25-40), most fresh fruits (30-50), minimally processed whole grains, milk, natural yogurt
Moderate IG	56 to 69	Basmati rice (58), wholemeal rye bread (65), oat flakes (60), sweet potato (63)
High GI	70 or more	White bread (75), cooked white rice (72), boiled potato (78), white sugar (65-70), puffed rice cakes (82)

2. Glycemic load: an even more useful concept

The glycemic index has an important limitation: it does not take into account the quantity of carbohydrates actually consumed. This is where glycemic load (GL) comes into play.

The glycemic load is calculated as follows: CG = (GI x quantity of available carbohydrates in grams) / 100A telling example: watermelon has a high GI (72), which could suggest that it is bad for blood sugar levels. But a 150g serving of watermelon only contains 8g of available carbohydrates. Its glycemic load is therefore: (72 x 8) / 100 = 5.8, which is very low. In practice, eating a slice of watermelon has minimal glycemic impact.

Glycemic load categories per meal:

• ●Low CG: 10 or less

• ●Moderate CG: 11 to 19

• ●High CG: 20 or more

The practical objective: aim for a total daily glycemic load of less than 100, and limit meals with high CG, particularly in the evening and during periods of sedentary lifestyle.

3. Factors that modify the glycemic index of a food

The same food can have a very variable GI depending on the way it is prepared and consumed. This is one of the most practical aspects of this concept: I can modulate the glycemic impact of my meals without fundamentally changing what I eat.

• ●Cooking: the longer a starchy food is cooked, the more its starch is gelatinized and the more its GI increases. Pasta cooked al dente has a GI of 40-50, compared to 60-70 for very cooked pasta. Boiled potatoes have a GI of 78, but cold potatoes (potato salad) go down to 55 thanks to the retrogradation of starch.

• ●The presence of fiber: fiber slows down the digestion and absorption of carbohydrates, lowering the overall GI of the meal. This is why wholemeal bread has a lower GI than white bread, and whole fruit has a lower GI than its juice.

• ●The presence of fats and proteins: the addition of fats and proteins to a carbohydrate meal slows gastric emptying and lowers the overall GI of the meal. Pasta with salmon and olive oil has a lower overall GI than the same pasta eaten alone.

• ●Acidity: acidic foods (lemon, vinegar, fermented foods) slow down the digestion of starches and significantly lower the GI of the meal. Adding balsamic vinegar to a rice salad can reduce its GI by 20 to 35%.

• ●The degree of maturity of the fruits: a very ripe fruit has a higher GI than a barely ripe fruit. Green bananas have a GI of 30, very ripe bananas 60.

• ●Particle size: finely ground flours have a higher GI than whole or coarsely crushed grains. This is why wholemeal rye sourdough bread has a much lower GI than ordinary baguette.

4. GI and chronic disease prevention

The clinical usefulness of the glycemic index and glycemic load is particularly well documented in the prevention and management of several chronic pathologies:

• ●Type 2 diabetes: a systematic review published in Diabetes Care (2008) showed that a low GI diet significantly improved glycated hemoglobin (HbA1c) in diabetic people. Low-CG diets are associated with better insulin sensitivity in prospective studies.

• ●Cardiovascular prevention: a high glycemic load is associated with an increase in blood triglycerides and a reduction in HDL cholesterol, two cardiovascular risk factors. The Nurses' Health Study showed an association between elevated GC and increased risk of coronary heart disease.

• ●Weight management: low GI foods prolong satiety and reduce insulin peaks which promote fat storage. Several meta-analyses have shown a modest but real advantage of low GI diets on long-term weight maintenance.

• ●Energy and cognitive performance: stable blood sugar levels throughout the day are associated with better cognitive performance, better concentration and a more stable mood - benefits that are particularly relevant in the context of corporate work.

5. Use IG every day without making it an obsession

The GI is a useful tool, not a food religion. Applying it intelligently without making it a source of stress or obsession is the key to beneficial use:

• ●I think in terms of meals, not isolated foods: the overall GI of a meal depends on the combination of all its ingredients. A balanced meal with protein, healthy fats and fiber will always have a moderate overall GI, regardless of the base carbohydrate food.- I replace refined cereals with their complete versions: this is the simplest and most impactful substitution. Wholemeal bread vs. white bread, wholemeal rice vs. white rice, wholemeal pasta vs. regular pasta.

• ●I favor legumes as main starchy foods: with a GI of 25 to 40, they are the best sources of low GI complex carbohydrates available.

• ●I systematically add a source of acid to my carbohydrate meals: a vinegar vinaigrette, lemon on the rice, mustard in the sauce. This simple gesture lowers the overall GI of the meal.

• ●I eat whole fruits rather than juice: the fibers in the pulp significantly lower the GI compared to juice without pulp.

• ●I cook my pasta al dente and I eat the cooled potatoes: two simple techniques to benefit from the nutritional benefits of these foods with a reduced glycemic impact.