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.

Managing your blood glucose does not just mean cutting down on simple carbohydrates – it means having a better understanding of how complex carbohydrates work. Certain types of carbohydrate, especially highly processed foods, such as white bread, release their sugars very quickly, which is unhelpful to you if you are controlling your sugar levels.

By keeping glucose levels fairly constant, you are more likely to avoid dips in energy, which can lead to cravings for sugary foods and the temptation to go for bigger portions of food.

Having a low glycaemic index (GI) diet

A very restricted diet, is not recommended when you are pregnant. However, choosing low glycaemic index foods more often, watching your portions, and limiting the amount of high glycaemic index foods you eat, can help you to manage your blood glucose levels. 

As a general rule, you need to replace foods with a high glycaemic index (such as white bread and sugary foods) with foods with a low to medium glycaemic index, such as wholegrain bread, brown rice, pasta, pulses, fish or chicken.

There are many factors that affect the GI rating of a food:

  • whether it is processed - this usually increases the GI rating
  • how much fibre it has - wholegrains (NOT wholemeal, which is ground up grains) and high-fibre foods increase the GI rating
  • how much protein it has - protein lowers the GI rating

This helpful spreadsheet from the Eurpoean Diogenes study has the levels of GI in many types of food.

The amount of carbohydrate you eat, and when you eat it, usually depends on several things, including how hungry you get, your blood glucose levels and your weight gain. You should aim to have at least 175g of carbohydrate per day.

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. Gemma, mum of one

Managing your glucose levels without cutting out carbs

Here are some tips for managing your glucose levels without cutting carbs out completely.

If you have gestational diabetes, you need to keep an eye on your fat content too. Fats do not contain carbohydrates, but they are very calorific, so if you need to manage your weight then it’s a good idea to keep your fat intake low.

Read more about diet and exercise with gestational diabetes

Read more about treatment for gestational diabetes


  1. NHS Choices [ accessed April 2015] What is the glycaemic index? http://www.nhs.uk/chq/pages/1862.aspx?categoryid=51 Review date: 23/08/2015
  2.  NICE (2015) Diabetes in pregnancy: management of diabetes and its complications from preconception to the postnatal period, National Institute of Health and Care Excellence https://www.nice.org.uk/guidance/ng3
  3. Institute of Medicine (2007) Dietary Reference Intakes: Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC, National Academies Press, 2002 IN doi: 10.2337/dc07-S048 Diabetes Care January 2007 vol. 30 no. suppl 1 S48-S65


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    Last reviewed on March 1st, 2015. Next review date March 1st, 2018.

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    Please note that these comments are monitored but not answered by Tommy’s. Please call your GP or maternity unit if you have concerns about your health or your baby’s health.

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