Understanding the glycaemic index

The glycaemic index is a measure of how quickly the foods you eat raise your blood sugar (glucose) levels. Knowing what foods to avoid can help control gestational diabetes.

You don’t need to go on special diets when you are pregnant. Try to eat a range of different foods each day. This will help you get the right balance of nutrients that you and your baby need.

Controlling your blood sugar levels

If you have gestational diabetes, the aim is to keep your blood sugar levels in the target range for pregnancy. Eating a healthy, balanced diet that is low in fat, sugar and salt, and high in fruits and vegetables, will help. 

But you should also try to choose low glycaemic index (low GI) carbohydrate foods. These can help to stop your blood sugar levels from rising very quickly, or ‘spiking’.

“Initially, I found the whole thing quite daunting. What would happen if I ate the wrong thing? My midwife was really helpful. She helped me put things into perspective and encouraged me to focus on taking things 1 day at a time and to keep a food diary. Eventually, I’d built up a collection of recipes for each meal that I knew could help maintain my glucose levels, which became routine for the rest of my pregnancy."


What is the glycaemic index?

The glycaemic index (GI) is a rating system that shows how quickly carbohydrate foods affect your blood sugar level when you eat or drink them.

High GI carbohydrates raise your blood sugar levels quickly, which is not good for you or your baby if you have gestational diabetes. Try to eat less of these foods, which include:

  • sugary drinks and treats (such as biscuits, cakes, sweets)
  • some breakfast cereals, fruity muesli and granola
  • white bread 
  • processed potatoes (oven chips, fries, waffles)
  • white rice
  • white flour products (pies, pasties, sausage rolls).

Lower GI foods are better if you have gestational diabetes, because they raise your blood sugar levels more slowly. These include:

  • vegetables 
  • most fruits (but limit sweeter fruits, such as grapes, mango or dates) 
  • beans and pulses (such as chickpeas, lentils)
  • wholegrain foods (such as wholegrain bread, jumbo porridge oats)
  • wholewheat pasta
  • brown rice
  • high-fibre bread (granary, rye, sourdough)
  • all-bran cereal, nutty muesli.

Lower GI choices for common food types

Here are some lower GI options of carbs that many of us eat most days. When you eat one of these types of food, try to choose a lower GI option.

  • Bread: wholegrain, granary, rye, seeded, sourdough, jumbo oat, wholegrain pitta, wholegrain chapati.
  • Potatoes: new potatoes in their skins, sweet potato, yam, plantain.
  • Pasta: all pasta is low GI, as long as you only cook until still firm inside ('al dente') and don’t have too much. Brown pasta is best of all.
  • Rice: basmati, long grain, brown.
  • Other grains: bulgur wheat, barley, couscous, quinoa. 
  • Breakfast cereals: home-cooked porridge, wholewheat options.

“I had plain porridge for breakfast, then a piece of fruit mid-morning and at lunchtime just a wholemeal sandwich and a yoghurt, and another piece of fruit in the afternoon.” 


Don’t only focus on GI

Making simple changes to your diet by swapping out some high GI foods for lower GI options can be very helpful. But the glycaemic index isn’t the only thing to think about when you decide what to eat.

Not all foods with a high GI are unhealthy, and not all foods with a low GI are good for you. 

If you focus only on the GI of foods, without looking at other aspects (such as sugar and fat content), your diet could be high in fat and calories.

If foods have a higher fat or protein content, the carbohydrates are broken down more slowly. This means their GI value is lower, but it doesn’t mean they’re good for you. 

Foods that are cooked in fat also have a lower GI value. For example, fried crisps have a lower GI value than baked potatoes. However, baked potatoes are still better for your health. 

Parsnips have a high GI, while chocolate cake has a lower GI value. This doesn’t mean you get to eat chocolate cake all the time!

Try to think about having healthy, balanced meals. These should be low in saturated fat, salt and sugar, and contain more fruit and vegetables, wholegrains, pulses, nuts and oily fish. 

The good news is that many low GI foods are high in fibre, which is a key part of a healthy diet. Just be sure to look at the whole nutritional label.

Don’t forget to eat regularly – usually three times a day – and don’t skip meals. It may help to spread your carbohydrate intake through the day and avoid having carbs for breakfast. This is because many people find carbs harder to process at breakfast time.

Also, remember that the amount of carbohydrate you eat has the biggest impact on your blood sugar levels after meals. It’s important to watch your portion sizes and not ‘eat for two’.

Gestational diabetes meal ideas

If you’re not sure where to start, check out our meals for gestational diabetes. We’ve listed lots of meals that could help you control your blood sugar levels, and covered breakfast, lunch, evening meals and healthy snacks. 

Diabetes UK also have some recipes for people with gestational diabetes that you might like to try.

Ask for help

If you have been diagnosed with gestational diabetes, you will get extra care throughout your pregnancy from a specialist healthcare team. 

This will include a dietitian, who can give you advice about your diet, how to plan healthy meals, and how to keep your blood sugar levels stable. If you’re in doubt, make sure you ask!

Learn more about gestational diabetes and your diet.

British Dietetic Association (Maternal and Fertility Nutrition Specialist Group) (2021). Gestational diabetes. Available at: https://www.bda.uk.com/static/e2c3fac8-7a56-4f89-849ac39e97f185fe/Gestational-Diabetes.pdf (Accessed January 2024) (Page last reviewed 02/2021. Next review due 02/2024)

NHS website (2022). Gestational diabetes. Available at: https://www.nhs.uk/conditions/gestational-diabetes/ (Accessed January 2024) (Page last reviewed 08/12/2022. Next review due 08/12/2025)

British Dietetic Association (nd). Food Fact Sheet: Glycaemic Index (GI). Available at: https://www.bda.uk.com/resourceLibrary/printPdf/?resource=glycaemic-index (Accessed January 2024) 

NHS website (2022). What is the glycaemic index (GI)? Available at: https://www.nhs.uk/common-health-questions/food-and-diet/what-is-the-glycaemic-index-gi/ (Accessed January 2024) (Page last reviewed 17/06/2022. Next review due 17/06/2025)

National Institute for Health and Care Excellence (2010). Weight management before, during and after pregnancy. NICE public health guideline 27. Available at: https://www.nice.org.uk/guidance/ph27 (Accessed January 2024) (Page last reviewed 28/07/2010)

National Institute for Health and Care Excellence (2020). Diabetes in pregnancy: management from preconception to the postnatal period. NICE guideline 3. Available at: https://www.nice.org.uk/guidance/ng3 (Accessed January 2024) (Page last reviewed 16/12/2020)

Review dates
Reviewed: 06 March 2024
Next review: 06 March 2027