Everything you need to know about gestational diabetes and diet

Gestational diabetes

One part of my day job is acting as the specialist dietitian for the gestational diabetes clinic. I therefore see quite a lot of women post diagnosis and of course it can be an anxious time for these women. They often present with a number of questions and I therefore thought I’d take a some time to discuss the dietary considerations for gestational diabetes.

What is gestational diabetes

Gestational diabetes is an inability for your body to control it’s blood glucose levels during pregnancy. This manifests as a result of the hormones produced during pregnancy interfering with the action of your body’s insulin. Essentially, your body develops some resistance to insulin meaning the cells are not as receptive to insulins message. This leads to some of the glucose in the blood being unable to enter the cells where it wants to go which results in an increase in blood glucose levels.

This can be diagnosed via two methods. A fasting blood glucose test first thing in the morning with a positive diagnosis of blood glucose levels above 5.6mmol/l. Alternatively, your midwife may give you a glucose containing drink and test your blood glucose levels 2 hours later. This is known as an oral glucose tolerance test or OTTG. If your glucose levels are above 7.8mmol/l this too is diagnostic.

Usually this test will not be conducted until around 26 weeks of your pregnancy unless you are identified as high risk such as previously developing gestational diabetes.

How is gestational diabetes different from other forms of diabetes

Gestational diabetes not permanent. It typically only lasts the duration of the pregnancy with blood glucose levels returning to normal once you have delivered your baby. Gestational diabetes usually becomes more difficult to manage as the pregnancy progresses. By the third trimester your body will develop it’s peak insulin resistance and therefore you may find it difficult to control your blood glucose levels during this period.

Developing gestational diabetes can be an indicator for an increased risk of developing type 2 diabetes in later life or actually flag preexisting type 2 diabetes. Therefore, we recommend if you develop gestational diabetes it is worth attending a yearly check up at your GP surgery following birth. It is also recommended following healthy living advice to help minimise your risk.

I’ve been diagnosed, now what

Depending on the service you have access to and the guidelines they follow, you will generally be asked to monitor you blood glucose levels 6 times per day. This means testing your blood glucose levels pre and post breakfast, lunch and dinner.

You will be given blood glucose targets depending on the time of day and ideally your levels will not exceed these. These are:

Under 5.3mmol/l upon waking

Under 6mmol/l between meals (i.e. before lunch and dinner)

Under 7.8mmol/l 1 hour after meals

The reason for this is these are the levels at which your baby is at no increased risk of harm. Allowing blood glucose levels to frequently go above this can lead to a number of issues with the birth and the baby it self.

Without gestational diabetes your body should be able to keep your glucose levels below these targets. Nonetheless, when talking any form of diabetes, these targets are quite tight and therefore the wrong dietary choices can lead to spikes in your glucose levels.

I’m measuring bloods glucose levels, what do the results mean

When you visit your gestational diabetes team they will look at your diary of blood glucose levels to help decide the next course of action.

The first measure we look at is the morning fasting test. This is a good indicator of how well your body is able to control it’s glucose levels independent of external influences such as food and activity. Usually if these figures are above the 5.3mmol/l target it will be indicative of some medication. There is nothing you can do about this figure unless eating late or throughout the night.

Upon waking our livers begin to release glucose in order to prepare the body for the day. In any form of diabetes this can be problematic and cause abnormal spikes in the morning despite not eating anything. We refer to this as the dawn phenomenon.

Measuring between meals, unless snacking, also give us an indication of how well the body is able to cope on its own. Post meal figures tell us how well your body is able to tolerate carbohydrate in your diet. If you are seeing regular spikes above 7.8mmol/l following meals it could mean you are having too many or the wrong type of carbohydrates at meals.


It is the carbohydrate containing foods in your diet which we are primarily concerned with in any form of diabetes. I have previously wrote about this and you can find here.


Ultimately, the biggest deciding factor in what your glucose levels do following a meal will be the total carbohydrate intake. Whether these come from starchy foods like bread, rice, pasta; natural sugars like fruit, milk sugars or processed sugars such as cakes, biscuits, chocolate, sugary drinks, it is the total amount which counts.

You can help the process by choosing lower glycaemic index (what the glycemic index is can be found here) foods such as wholegrain cereals and breads, sweet potatoes, new potatoes, basmati or brown rice, brown pasta, oats, fruit, vegetables and avoiding mashing or juicing foods. However, this can be seen as just another tool in your toolbox to help you control your glucose levels. It is the total carbohydrate which will make the biggest difference.

We recommend keeping carbohydrate foods to no more than a fist portion at meal times. However, we appreciate pregnant ladies may have an increased appetite. Therefore we do not say eat less but instead replace your usual carbohydrate portion with foods which will not effect your glucose levels like vegetables or protein based foods like meat, fish, eggs, nuts, beans, pulses and lentils.


Most ladies who are going to spike will typically spike following breakfast. This is because of the dawn phenomenon I previously mentioned but also due to our staple breakfast foods. In the UK breakfast tends to consist of cereal, toast, or oats. Some of these foods can be low glycaemic index but they are all primarily carbohydrate. Combine this with the dawn phenomenon and you may find some ladies spike at breakfast.

Therefore, breakfast is a prime example of how we can reduce the total carbohydrate intake and replace it with vegetable or protein foods. One example is if you have two slices of toast for breakfast and are finding your glucose levels spike, you can replace one slice of toast with an egg or two. Another alternative is to have a more continental style breakfast incorporating some vegetables – perhaps cooked in an omelette, cooked meats/fish, a small amount of fruit in yogurt amongst many other examples.

Essentially you are only limited by your own imagination using the principle that vegetables and protein based foods are mostly neutral on blood glucose levels. If you are against moving away from carbohydrates in the morning, I would recommend trying the lower glycaemic index carbohydrates first to see if this helps.

Lunch and dinner

The other meals of the day can also cause spikes in your glucose levels. You may find you see less spikes than at breakfast for three reasons.

First, the dawn phenomenon has warn off by lunch.

Second, because we eat more variety at these meals it can mean less carbohydrate in total is eaten.

Third, we also eat more protein and fat at these meals which act to slow down the absorption of carbohydrates.

Fat and protein

When eating carbohydrates in combination with fat and protein it can act to slow the absorption of the carbohydrate. You basically get less carbohydrate entering the system at any one time. Again, this doesn’t mean by eating more fat and protein you can eat as much carbohydrate as you wish because remember the biggest factor in your blood glucose response is the total carbohydrate eaten.


It is good practice to try to combine a variety of foods groups at each meal. As a rule we say half the plate should be dedicated to vegetables with a quarter to protein and a quarter to carbohydrates. If you can’t tolerate vegetables, bulk out the plate with lean protein choices like poultry, fish, eggs, or lean beef.

This will help to keep the total carbohydrate content of the meal lower and help to slow the absorption of it once entering digestion.

Choose lower glycaemic index foods to further help slow absorption and ensure you are having plenty of nutritious food.

Fruits do not need to be avoided but aim to eat no more than one portion at a time. A portion is 2 small fruits i.e. kiwi, clementine, 1 medium fruit like an apple or a quarter to a half of a larger fruit like a mango or a handful of grapes, berries, etc. Be cautious of dried fruit as this has a very high sugar content. Aim to spread out your fruit intake throughout the day and maybe limit yourself to no more than 3 portions per day.

Snacks follow the same principles. Good examples can be crisp breads, oat cakes, nuts, seeds, fruit, pre-packed protein pots made of meat, fish or beans, pulses or lentils or vegetable sticks with hummus.

Limit the amount of processed sugar you eat including foods such as sweets, biscuits, cakes, chocolate, or sugary drinks.

If you find your levels are spiking or you have eaten something you know will push you high, aim to go for a 20 minute walk after meals. This will help to reduce your figures.


Some ladies will have perfect glucose scores despite what they eat and others will have a near perfect diet and see spikes. It is all to do with the hormones of the pregnancy effecting your insulins ability to control your glucose levels. Therefore, if you are trying everything in your power to control the glucose levels with no luck, do not worry.

There is a balancing act as there is only so much you can cut back in the diet before it becomes restrictive and unrealistic. Some ladies are happy to go virtually carbohydrate free but as nutritionists we do not tend to recommend such measures. Therefore, patients who really struggle to control their glucose levels despite eating virtually no carbohydrates may benefit from the addition of some medication. Alternatively, you may eat a normal or high carbohydrate diet and not want to change this. Again, medication may be a good alternative in this instance. There are no harmful effects to the baby by commencing medication and this will allow you to have more flexibility in your diet. Have a conversation with your gestational diabetes team explaining your thoughts on the diet and see what they think is the best management strategy.


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