Reading labels
The carbohydrate line is the one you dose against. What it means, where it hides, and what the rest of the label adds.
The number that matters most for insulin is the carbohydrate figure, because carbs are what raise your glucose and what you dose against. Everything else on the label is useful, but that one line is the one you actually work with.
- Look at carbohydrate (the total grams that turn into glucose in your blood), not fat or protein, when you’re deciding a mealtime dose.
- Check whether the figure is per 100g or per portion, because the two can be wildly different and mixing them up throws the whole sum off.
- The “of which sugars” line sits inside the total carb figure, so you don’t add it on top; it’s already counted.
- Reading the carb figure too high means too much insulin and a hypo (glucose dropping too low); reading it too low means glucose runs up instead.
- Weighing the food beats guessing from the packet, because a “portion” on the label is rarely the amount on your plate.
Total carbohydrate is the line you dose against
UK food labels give you carbohydrate two ways: per 100g, and often per portion. The per 100g figure is the one that lets you do your own maths, because you can weigh what you’re actually eating and scale from there. The per-portion figure is only accurate if you eat exactly the portion the manufacturer decided on, which almost nobody does.
Under total carbohydrate you’ll see “of which sugars”. That’s not a separate thing to count. It’s telling you how much of the total is sugar rather than starch, and it’s already inside the bigger number. If a label says 30g carbohydrate, of which 12g sugars, the figure you care about is 30, not 42.
A misread label moves glucose in both directions
Getting the carb figure wrong isn’t a maths quibble, it changes where your glucose ends up. If you read the number as bigger than it really is, or dose for 80g when you ate 40, you can take more insulin than the food needs and your glucose can drop too low. That’s a hypo, and with a big overshoot it can arrive fast. If you read the number smaller than it really is, the food outruns the dose and glucose climbs instead.
So the label sum isn’t about being tidy. It’s the thing standing between a reasonable dose and a glucose that heads off in one direction or the other. That’s why the per 100g versus per portion question below matters more than it looks.
Per 100g versus per portion
This is where most label sums go wrong, and it’s not a knowledge gap, it’s a design problem. A cereal box might say 76g carbohydrate per 100g, and 30g per 45g serving. Both are true. But if you pour out 80g of cereal (easy to do) and dose for the 30g portion figure, you’ve counted less than half of what you ate, and your glucose will climb through the afternoon.
The fix is boring and it works: weigh the food, use the per 100g figure, and scale. Kitchen scales cost a few pounds and take the guesswork out of the part of this that most affects your glucose. Over time you’ll eyeball familiar meals, but early on, and with anything new, the scale is the honest answer.
Carbs aren’t the whole picture
A label tells you grams of carbohydrate. It doesn’t tell you how fast those carbs will hit, or what the fat and protein alongside them will do. A meal high in fat, a curry, a pizza, a takeaway, tends to slow how quickly glucose rises and can push it up for hours afterwards, long after a normal dose has finished working. The carb figure gives you no hint of that.
So reading a label well gets you the starting number. It doesn’t get you the shape of the whole meal. That’s not a failure of the label, it’s just the limit of what a packet can know about your body. The rest you learn by watching what actually happens after you eat.
What changes how a label lands for you
The same 30g of carbohydrate does not behave the same in every meal or at every time of day. Fat and protein slow it down. Your insulin-to-carb ratio (how much insulin covers a given amount of carbohydrate) may differ at breakfast versus dinner. And cooked pasta weighs very differently from dry pasta, so check whether a label figure is for the raw or cooked food. Labels are a starting point, not a verdict.
Reading a label in real situations
Examples, not instructions or doses.
You pour a bowl without thinking and it looks like a normal amount. The box says 30g carbohydrate per 45g serving. You weigh it: 85g. That’s closer to 57g of carbohydrate, not 30. Dose for 30 and glucose runs up; the label wasn’t wrong, the portion was just bigger than the one printed on the side.
A yoghurt says 15g carbohydrate, of which 11g sugars. You only need the 15. The sugars line is inside it, telling you most of these carbs come from natural and added sugar rather than starch. Add the sugars on top by mistake and you’ve dosed for 26g of food that was only 15, which can pull your glucose low.
There’s no packet to read. You’ve dosed for roughly the carbs, and two hours later you’re fine, but by hour four your glucose is climbing. That’s the fat and protein arriving late, which no label could have told you.