How We Calculate Real-Life GL

Look up the GI of each carb food

Glycaemic index (GI) ranks how quickly a food's carbohydrate raises blood sugar compared with pure glucose. We take GI values from the International Tables of Glycemic Index and Glycemic Load Values 2021, the standard reference compiled from published studies [1]. Where a specific branded product isn't listed, we use the closest matching food and say so.

Calculate the standard GL

Glycaemic load (GL) combines GI with how much carbohydrate you actually eat. For each carb food in the recipe:

GL = GI × available carbs (g) ÷ 100

We add these together to get the calculated GL for the whole meal. Available carbs means total carbohydrate excluding fibre, which is how UK food labels already list it.

10 or underLow
11–19Medium
20 or overHigh

Adjust for protein and fat

GI values are measured on foods eaten on their own. In a real meal, protein and fat slow digestion and lower the blood sugar response. Without an adjustment, calculated GL overestimates the real response.

Researchers Wolever and Bhaskaran estimated that each gram of protein lowers the glycaemic response by about 1.3%, and each gram of fat by about 0.4%, with the two effects adding together. Applying these corrections to published meal data reduced the overestimate from 32% to 11% [2]. A later study using an adjusted model of this kind correctly predicted the measured GI of 15 out of 17 mixed meals [3].

Reduction (%) = (1.3 × protein g) + (0.4 × fat g), capped at 40%
Real-life GL = calculated GL × (1 − reduction)

We cap the reduction at 40% because the published figures come from meals with smaller amounts of protein and fat than many of our recipes. Capping keeps our estimates conservative.

For readers with PCOS or type 2 diabetes: a separate study found that the glucose-lowering effect of protein didn't depend on how insulin resistant a person was [4].

Worked example

The Glucose Steady Full English

Carb food	GI	Available carbs	GL
½ tin baked beans (~200g)	40	26g	10.4
1 slice Jason’s Grains & Seeds sourdough	54	19g	10.3
Chicken sausages and roasted tomatoes	–	small	~3
Calculated GL			~24
Adjustment: (1.3 × 51g protein) + (0.4 × 37g fat) = 81%, capped at 40%			−40%
Real-life GL			~14

The sourdough’s GI isn’t published, so we use 54, the value for white sourdough. Figures are rounded. For comparison, a typical café fry-up (bacon, sausages, a full portion of beans, white toast and a hash brown) comes to a real-life GL of around 27–30 by the same method. See the full recipe.

What this number is, and isn't

It's an estimate, not a measurement. No one has measured these exact meals in a lab. The method is published and repeatable, so anyone can check our numbers.
We don't adjust separately for fibre. Fibre in each food is already reflected in its GI value, so counting it again would double-count it.
Your response may differ. Blood sugar responses vary between people and from day to day, depending on sleep, activity, stress and what you ate earlier.
This isn't medical advice. If you have diabetes, PCOS or another condition, or take medication that affects your blood sugar, speak to your GP or care team before changing how you eat.

References