Glycemic index and glycemic load

Not just a diabetes thing.

The glycemic index (GI) measures how fast a food raises your blood sugar after you eat it. It is expressed relative to a reference food assigned the value 100: here glucose = 100, the most widely used convention, which you can change in your preferences (some studies use white bread as the reference, which gives values roughly 1.4 times higher for the same food).

⚠️ That 100 is a benchmark, not a ceiling: it is a ratio to the reference food, not a percentage. A food absorbed faster than the reference therefore goes past 100. On the white bread scale, pure glucose reaches 143, which is why the "high" threshold lands exactly on 100 there: above it, you raise blood sugar faster than white bread does.

Low GI < 55

Slow absorption, steady blood sugar: lasting fullness, constant energy

Medium GI 55-70

Moderate absorption

High GI > 70

Fast absorption, a blood sugar spike followed by a crash: fatigue, cravings, irritability

› 1. GI and carbs: two different things

A food can be low in carbs but high GI, high in carbs but moderate GI, or both at once. These are two complementary measures, not interchangeable ones.

🍉 Watermelon

GI 72

Very fast absorption, but so few available carbs (7.5g/100g) that the real spike stays limited, unless you eat a lot

🫘 Lentils

GI 29

14g of available carbs per 100g, but fiber and protein slow absorption right down

🥔 Baked potato

GI 85

~20g of available carbs per 100g on top of a very high GI: both factors add up, immediate blood sugar spike

It is not just how much sugar you eat: it is how fast it reaches your blood.

› 2. Glycemic load: combining GI and quantity

GI has a limit: it says nothing about how many carbs you actually eat. That is where glycemic load (GL) comes in, combining the two:

GL = GI × available carbs (g) / 100

Low GL < 10 Moderate GL 10–20 High GL > 20

Take watermelon again: high GI (72), but so few available carbs (7.5g/100g) per serving that the real glycemic load stays low. Conversely, a food with a moderate GI but very high in carbs can carry a high glycemic load.

🍉 Watermelon

GL 3.6

High GI (72), but only 7.5g of available carbs per 100g: the real load on blood sugar stays low

🍚 Cooked white rice

GL ≈ 20

High GI (73), and ~28g of carbs per 100g: the glycemic load climbs sharply

🥖 White baguette

GL ≈ 52

High GI (95) and very high in carbs (~55g/100g): the worst of both worlds, a major blood sugar spike

You can compare the GL of every fruit on the Fruit page (column hidden by default, switch it on under "Filters").

› 3. Why this concerns you, not just people with diabetes

A high GI triggers a strong insulin release to bring blood sugar back down. That rapid drop brings on fatigue, a dip in focus, sometimes irritability: the familiar afternoon slump. Over the long run, repeated spikes encourage insulin resistance and weight gain.

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Energy

High GI = fast rise then sharp crash. Low GI = steady energy that lasts.

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Mood & focus

The blood sugar crash brings irritability, brain fog, trouble concentrating.

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Sleep

A high GI in the evening activates the nervous system and delays falling asleep. The blood sugar crash that follows can cause micro-awakenings. Choosing a low GI in the evening supports deep, restorative sleep.

› 4. Insulin resistance

Normally, insulin acts as a key that opens cells to let glucose in from the blood. With repeated blood sugar spikes, the pancreas has to produce more and more insulin to do the same job. In time, cells get used to it and "ignore" the signal: that is insulin resistance.

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What happens

Glucose stays in the blood longer. The pancreas wears itself out producing ever more insulin. The liver stores the excess glucose as fat.

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The long-term risks

Type 2 diabetes, metabolic syndrome, cardiovascular disease.

It is a silent process that sets in over years, often with no visible symptoms at first. You can develop insulin resistance long before being diagnosed with diabetes.