- The glycemic index in one minute
- Low, medium and high GI bands explained
- Everyday foods and where their GI falls
- What can change a food's GI score
- Why the glycemic index isn't the whole story
- Using GI sensibly day to day
- When to talk to a professional
- Sharing what you know about food and nutrition
- Frequently asked questions
The glycemic index (GI) is a scale from 1 to 100 showing how quickly a carbohydrate food raises your blood glucose. NHS sources class under 55 as low, 55 to 70 as medium and over 70 as high. It's a guide, not a verdict on whether a food is good for you.
You've probably seen "low GI" on a loaf of bread or heard it mentioned in a diet conversation and wondered what the number means. It's a fair question, because the glycemic index (spelled glycaemic in the UK) is one of the most quoted and most misunderstood ideas in everyday nutrition.
I've pulled this together from NHS trust and NHS Scotland patient information, so you get the plain version. It's general education only. If you have diabetes or any health condition, a GP, dietitian or diabetes team is the right person to tailor advice to you.
The glycemic index in one minute
NHS Scotland's My Diabetes My Way describes the glycaemic index, or GI, as a scale from 1 to 100 that shows how quickly a carbohydrate food raises the level of glucose in your blood. Foods that break down fast during digestion release glucose quickly and score higher. Foods that break down slowly release it gradually and score lower.
The scale only applies to foods that contain carbohydrate. Cheese, meat, fish and eggs have little or no carbohydrate, so they don't get a GI value at all.
Low, medium and high GI bands explained
The NHS sources I read use the same three bands:
| GI band | Score | What it suggests |
|---|---|---|
| Low | Under 55 | Glucose is released more slowly |
| Medium | 55 to 70 | Somewhere in the middle |
| High | Over 70 | Glucose is released quickly |
One small wrinkle: some hospital leaflets write the medium band as 56 to 70, which only matters for a food scoring exactly 55. Don't worry about it. The point is the general direction, not the last digit.
Everyday foods and where their GI falls
Kent Community Health NHS Foundation Trust publishes a GI chart with values per 100 grams. A few examples from it show how varied everyday foods are:
| Food | GI value | Band |
|---|---|---|
| Oats | 50 | Low |
| Apple | 30 | Low |
| Basmati rice | 50 | Low |
| White long-grain rice | 60 | Medium |
| Baked potato | 69 | Medium |
| White bread | 75 | High |
| Watermelon | 75 | High |
| Cornflakes | 93 | High |
You'll notice some surprises. Watermelon is high GI, yet it's still a fruit with real nutritional value, which is exactly the caveat NHS Scotland flags: a high GI doesn't automatically mean a food is bad.
What can change a food's GI score
GI isn't a fixed label stamped on a food. The same ingredient can score very differently depending on how it's prepared. The Kent chart gives some clear examples:
- Ripeness: green bananas score 30, while well-ripened bananas score 65.
- Cooking: raw carrots score 35, cooked carrots 85.
- Form: fresh apricots score 20, dried apricots 35.
- Type of rice: long-grain white rice scores 60 and instant white rice 70.
- What it's eaten with: pairing carbohydrate with protein, healthy fats or vegetables helps moderate the effect on blood glucose.
That last point matters most in real life, because most of us eat mixed meals rather than single foods. NHS Scotland gives the example of a high-GI baked potato eaten with low-GI baked beans, which together make a medium-GI meal.
Why the glycemic index isn't the whole story
NHS Scotland makes a point that's easy to miss: the amount of carbohydrate you eat matters at least as much as its GI. A large portion of a low-GI food can still raise blood glucose substantially, and NHS Scotland says the carbohydrate load matters more than the type.
It also warns that low GI doesn't mean healthy. Ice cream, nuts and chocolate sit in the low to medium range but are high in fat and calories, so they're foods to enjoy in small amounts. A GI number tells you about one thing, the speed of glucose release, and nothing about vitamins, fibre, salt or fat.
Fibre and vitamins matter too. If you'd like to understand the nutrients a GI chart can't show you, my explainer on what micronutrients are and where they come from is a good companion read.
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Using GI sensibly day to day
The NHS guidance I read suggests treating GI as a tool rather than a rulebook:
- Look at the whole meal, not single ingredients.
- Choose lower-GI carbohydrates, such as oats, basmati rice, wholewheat pasta or apples, as the base of meals and snacks.
- Add protein, healthy fats or salad and vegetables to carbohydrate-rich meals.
- Don't cut out high-GI foods completely. Many are nutritious.
- Keep portions of carbohydrate in mind as well as the type.
Drinking enough through the day is part of general healthy eating too, and I've covered the official guidance in my piece on how much water you should drink a day.
When to talk to a professional
If you have diabetes, are pregnant, or manage another condition affecting blood glucose, don't change how you eat based on a chart alone. The Kent trust's leaflet is clear that its guidance should be followed on the advice of a healthcare professional. Your GP, practice nurse, diabetes team or a registered dietitian can build a plan around your own needs and medicines.
Sharing what you know about food and nutrition
If you're a dietitian or nutrition writer who explains topics like GI to everyday readers, there's an audience that would value your expertise.
Dietitians and nutrition writers can find nutrition blogs that accept contributor articles here.
Frequently asked questions
Is a low GI food always a good choice?
No. NHS Scotland points out that foods such as ice cream, nuts and chocolate have a low to medium GI but are high in fat and calories, so they're best in small amounts.
Do all foods have a GI value?
No. Foods with little or no carbohydrate, such as cheese, meat, fish and eggs, don't have a GI value.
Why does cooking change the GI of a food?
Cooking can make carbohydrate easier to digest, so glucose is released faster. The Kent trust chart lists raw carrots at 35 and cooked carrots at 85.
Should I avoid high GI foods completely?
Not necessarily. High-GI foods such as watermelon can still be nutritious, and the overall mix of a meal matters more than any single item.
Does the amount I eat matter as well as the GI?
Yes. NHS Scotland explains that the amount of carbohydrate you eat matters as much as its GI, so portion size still counts.
Who should I ask about using GI if you have diabetes?
Speak to your GP, diabetes team or a registered dietitian. They can tailor advice to your medicines and your own targets.
