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Understanding the glycaemic index

The glycaemic index is a measure of how quickly sugars are released into the bloodstream. Knowing what foods to avoid helps control gestational diabetes.

Controlling your glucose levels

You don’t need to go on special diets when you are pregnant. It’s important to eat a variety of different foods every day to get the right balance of nutrients that you and your baby need.

If you have gestational diabetes, the aim is to keep your glucose 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 include good-quality low glycaemic index (GI) carbohydrate foods.

It may help to spread your carbohydrate intake through the day and avoid carbs for breakfast (many women find carbs harder to process at breakfast time.

“Initially, I the whole thing quite daunting. What would happen if I ate the wrong thing? My midwife was really helpful. She helped my 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 glucose level.

High GI carbohydrates raise your glucose levels quickly, which is not good for your baby if you have gestational diabetes. These foods include:

  • sugary drinks and confectionary (biscuits, cakes, sweets, chocolate etc)
  • breakfast cereals, muesli and granolas
  • white bread
  • processed potatoes (oven chips, french fries, waffles)
  • white rice
  • white flour products (pies, pasties, sausage rolls).

Low or medium GI foods are better for you because they raise your glucose levels slowly. These include:

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

Here are some everyday carbs with examples of a lower GI choice:

Bread: lower GI choices include multigrain, granary, rye, seeded, wholegrain, jumbo oats, pita bread and wholemeal chapatti.

Potatoes: lower GI choices include new potatoes in their skins, sweet potato and yam.

Pasta: all pasta is considered low GI, but you should cook until al dente and watch your portion size.

Rice: lower GI choices include basmati rice, long grain rice and brown rice.

Other grains: lower GI choices include bulgur wheat, barley, couscous and quinoa.

Breakfast cereals: lower GI choices include home-cooked porridge, all bran, bran buds and shredded wheet.

“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. At tea-time I’d have something like a baked potato with chilli but small portions.” 


Don’t only focus on GI

Making some simple changes to your diet by replacing some high GI foods with lower GI alternatives can be very helpful. But try not to rely only on the glycaemic index when you decide what to eat.

Keep in mind that not all foods with high GI are unhealthy and not all foods with a low GI are healthy. For example, 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! If you focus only on the GI of foods, without looking at other aspects (such as sugar and fat content), your diet could be unbalanced and high in fat and calories.

It’s important 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. 

Also try to remember that it is the amount of carbohydrate you eat, rather than its GI rating, that has the biggest influence on your glucose levels after meals. It’s important to watch portion sizes and not ‘eat for two’.

Ask for help

There’s a lot of information out there about eating well, so try not to get overwhelmed. Remember that 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 keep your glucose levels stable.


NHS Choices. Treatment. Gestational Diabetes (Page last reviewed: 06/08/2019 Next review due: 06/08/2022)

The Association of UK Dietitians. Glycaemic Index. (Page last reviewed: January 2017. Next review date: January 2020)

NHS Choices. What is the glycaemic index (GI)? (Page last reviewed: 23/07/2018 Next review due: 23/07/2021)

NICE (2015). Diabetes in pregnancy: management from preconception to the postnatal period. National Institute for health and care excellence

Review dates
Reviewed: 24 July 2020
Next review: 24 July 2023

This content is currently being reviewed by our team. Updated information will be coming soon.