GI – more complicated than it sounds!

GI, or glycemic index, is a term that first saw the light of day in 1981, in the prestigious American Journal of Clinical Nutrition. It was a research group at the University of Toronto, led by nutrition professor David Jenkins, who presented results of a clinical study. The group had examined how fast and steep blood sugar rose after eating various carbohydrate-rich foods. Neither Jenkins nor any of his colleagues could have any idea what impact the concept would have for many decades to come.

Until this study, which was soon followed by several more, all carbohydrates had been considered equal. This meant, among other things, that only the amount and not the quality of the carbohydrates was used to calculate the dose of insulin a diabetic needed in connection with a meal. It was now established that different carbohydrates had completely different effects on the blood sugar rise, and the road was open for a more precise insulin dosage.

As the GI concept gained a foothold and spread worldwide, several diets also emerged more or less firmly entrenched in the concept. GI and Atkins are the best known, but there is also a long list of more or less extreme protocols – such as LCHF, Keto, and Paleolithic diets – that involve removing as much carbohydrates as possible from the diet. I do not intend to enter into the discussion of the pros and cons of these diets, but note that a reasonable proportion of high-quality carbohydrates in the diet works well for most people.

What then are good and bad carbohydrates? Simply put, the “fast,” i.e., those with a high GI, which give a high and fast rise in blood sugar, are more difficult for the body to handle. The “slow” ones, on the other hand, give a lower and slower rise that is kinder to the body and provide a more prolonged feeling of satiety. Fast ones are, for example, white bread, breakfast cereals, several kinds of rice, French fries, and everything that contains refined sugar. Slow are, for example, bread where the grain has been allowed to retain part of its structure, such as whole or cut kernels, beans, peas and lentils, and pasta cooked to retain its chewing resistance.

But at the same time, it is (unfortunately) not that simple. A food ingredient with a high GI isn’t necessarily worse than one with a lower GI. Several different factors determine how what we eat affects blood sugar. Take boiled potatoes and pasta as examples. The carbohydrates in potatoes are fast, but at the same time, the potatoes contain so much water that they give a good feeling of satiety without us getting so many calories.

On the other hand, the pasta contains a much higher proportion of carbohydrates, which means that we get many more calories before we are full. This is one reason why the term “glycemic load” (GL) is sometimes used instead, where a food’s GI is multiplied by the content of carbohydrates in a meal. GL makes it easier to compare regular servings of different foods and their expected effect on blood sugar.

And as if this was not complicated enough, the rise in blood sugar is also affected by the composition of the whole meal and, in fact, by the order in which we eat the different ingredients. An ingredient with a high GI, say white rice, can be compensated with another, for example an acidic salad dressing that lowers the blood sugar response. Research shows that if we start the meal with a small amount of protein – for example in the form of soup or a piece of chicken before the fried potatoes – it reduces the effect of carbohydrates on blood sugar. Therefore, it may be wise to serve, e.g., nuts, olives, or cheese as an aperitif instead of chips or white bread.

To sum up, I do not think one should focus too narrowly on GI to decide how wholesome food is. It’s better to learn principles such as that whole structures are better than decomposed, soured products (including sourdough bread) are better than unsoured and eating the breakfast egg before the sandwich or porridge. As long as we make sure to get a variety during the day and week, we can eat most foods. But it is good to know that some simple things can make a massive difference to well-being and health. Also, do not forget to notice how different foods and eating patterns make you feel. There is a lot to learn there.

Want to know more? Here are some links.

Glycemic index of foods: a physiological basis for carbohydrate exchange

International table of glycemic index and glycemic load values: 2002 

Mechanisms through which a small protein and lipid preload improves glucose tolerance

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