Gestational diabetes diet – everything you need to know

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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 a gestational diabetes diet and help you understand the condition more clearly.

What is gestational diabetes

Gestational diabetes is an inability for your body to control it’s blood glucose levels during pregnancy. This happens because the placental hormones being produced during pregnancy interfere with how your body controls its glucose levels. Insulin is the hormone in your body which helps to lower blood glucose levels. In gestational diabetes, your body develops some resistance to insulin meaning the cells in your body struggles to lower its glucose levels like normal. As a result, some of the glucose in the blood is unable to enter the cells where it wants to go which results in an increase in blood glucose levels.

This is usually 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.

With the covid 19 pressures, some trusts have moved to random glucose sampling and have increased the threshold to 9mmol/L. 

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 is 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.

Risk factors for developing gestational diabetes

There’s a few factors that contribute to how likely you are to develop gestational diabetes. These factors are similar to the risk factors for developing type 2 diabetes and this is why people who have gestational diabetes are at an increased risk of developing type 2 diabetes later in life. 

Such factors include: 

  • Age (being over 35 increases the risk) 
  • Ethnicity (South Asian and Afro Caribbean heritage increases the risk)
  • Weight and lifestyle
  • History of polycystic ovarian syndrome 
  • Family history of diabetes 
  • Genetics 

Obviously most of these you cannot change. Lifestyle and body weight are 2 modifiable risk factors to help reduce the risk going into pregnancy or once diagnosed. The risk will also increase if you have more than one risk factor. 

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 (or under 6.4mmol/L 2 hours later)

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 itself.

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.

Waking levels

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 regularly above the 5.3mmol/l target it may be indicative of some medication. However, your diabetes/obstetric team can discuss this with you.

Upon waking our livers begin to release glucose in order to prepare the body for the day. The hormones released from the placenta and other hormones designed to get you out of bed in the morning are also at their highest level in the morning.  Therefore, patients find themselves prone to glucose spikes upon waking and at breakfast. 

If your glucose levels are over 5.3mmol/L upon waking, it doesn’t necessarily mean you are doing anything wrong. So try not to be too hard on yourself. It is mostly hormonal. 

How to lower high waking glucose levels

From experience there are 2 main factors that can help control waking levels. As mentioned above medication may be recommended. This will usually be a tablet known as Metformin or insulin. Metformin is taken between once and four times a day.

There are many different types of insulin regimens but to help high waking levels only, normally only one insulin injection a day will suffice.

Both medications have extensive research about their safety in pregnancy and your medical team can discuss this with you. 

The other factor that may effect your waking glucose level is how active you were the day before. Often ladies who are more active have lower waking values compared to the days they are more idle. How much is enough will depend on the individual. 

If you have a high reading in the morning, try not to stress too much. Try some exercise throughout the day to see if it helps your overall and waking levels. However, try not to over do it as we appreciate you’re also carrying a little one. 

Other factors that may cause variable waking levels include the time you wake up (those hormones vary throughout the day) and whether you ate overnight or not. There are also many factors that can additionally effect them. Not everyone will experience a high reading and ultimately, for most people, it is just a hormonal response. 

Gestational diabetes diet

The dietary advice for gestational diabetes is primarily concerned with keeping glucose levels within target. However, this doesn’t replace the other dietary advice normally provided in pregnancy regarding food safety and supplementation.

Make sure if you’re diagnosed early in the pregnancy you continue to take your 400mcg folic acid supplement daily. If you have existing diabetes, this needs to be increased to 5mg once daily. 

You can find this advice on the NHS website, which you can access here. 

There are also foods you should avoid in pregnancy.  For more information visit the NHS website you can find here. 


Ultimately, the biggest deciding factor in what your glucose levels do following a meal will be the total carbohydrate intake. We’ve blogged lots about carbohydrates here in the past.  However, we’ll give you a quick summary.  

Carbohydrates are found in any starchy foods such as bread, pasta, rice, cereal, dhal, oats, potatoes, pastry and to a much smaller extent, beans, pulses, lentils and chickpeas. 

Sugar is also a type of carbohydrate. These can be either processed or natural sugars. Processed sugars are products like cake, biscuits, sweets, jam, marmalades but also include juice, sugary drinks and honey.

Natural sugars include fruit and a small amount of natural sugar in milk and yogurt called lactose. Natural sugars have much less sugar in them compared to process sugars and so are less likely to cause high glucose readings. 

Whether the carbohydrates come from starchy foods like bread, rice, pasta, natural sugars like fruit and milk or processed sugars such as cakes, biscuits, chocolate, sugary drinks, it is the total amount which counts. Some foods may push your glucose levels higher much quicker than others. 

Foods not effecting glucose levels

Foods that have no or very little effect on glucose levels come from some of the other food groups. Protein foods such as meat, fish, eggs, nuts and seeds, do not effect glucose levels. Vegetables and salad have very small amounts of carbohydrate and therefore are considered mostly neutral in terms of their glucose effect. Finally, fat does not effect glucose levels. Meaning foods like fat, butter, oils, cheese and avocados do not effect glucose levels. 

Remember though, high fat foods provide many calories and therefore eating too much may cause additional weight gain during the pregnancy. Although, in reality, the dietary changes made from lowering your carbohydrate intake often compensates. 

The difference in how quickly carbohydrates are absorbed 

Not all carbohydrate containing foods are digested and absorbed at the same speed. Some get into your body very quickly increasing the likelihood of a high glucose level. Whereas others are more slowly absorbed and therefore less carbohydrate enters your system at any given time. 

This is called the glycaemic index or GI. Again we have blogged about this previously, which you can find here (what the glycemic index is can be found here).

Ultimately, replacing high glycemic index foods (quickly absorbed) with low glycaemic index foods (slowly absorbed) can act as another tool to help lower glucose levels.

High GI foods include white starchy foods like white bread, pasta, rice, mashed potato, juice, crisps, cereal with milk, tropical, dried or overly ripe fruits and sugary foods. 

Low GI foods include brown, wholegrain or granary rice, pasta and bread, sweet potatoes, new potatoes, basmati or brown rice, brown pasta, oats and overnight oats, most other fruits (apples, berries, oranges etc), vegetables, beans, pulses and lentils and avoiding mashing or juicing foods can help. 

Food pairing

Fat, protein and fibre also helps to lower the glycaemic index by slowing down the absorption of foods. For example, a slice of toast by itself may be absorbed more quickly than a slice of toast with an egg on it. An apple may be more slowly absorbed with some peanut butter on it. A full meal with protein and vegetables alongside the starch will be more slowly absorbed compared to a bowel of cereal. 

However, 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.

In fact, adding extra fat for the sake of it is often not necessary. However, if certain foods are causing high glucose levels, you could experiment with food pairing. 

General advice

We’ll look at advice for the individual meals in a moment. In the meantime, there are some general principles we can summarise here.

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.

If you find even a fist is too much, you can continue to reduce your portion size whilst replacing this with vegetables and protein. For example, move from a fist, to a palm size. 

Also replace high GI foods with low GI foods and this way you are giving yourself the best chance of not having glucose spikes after meals. 


Most ladies who are going to spike will typically spike following breakfast. This is because your hormones are at their most active in the morning and also because most of our staple breakfast foods are carbohydrate heavy.

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 hormonal effect 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.

If you do spike after breakfast, as first line advice, try replacing high GI foods with low GI foods. An example is replacing cereal with porridge oats. If this doesn’t work, you can take one step further and move to overnight oats and/or make the oats with full fat yogurt. 

Remember though, it is the total carbohydrate that will be the biggest factor on your glucose response. Therefore, if lower GI options do not work, then you may have to lower your total carbohydrate intake.

One example of how to do this 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. Perhaps even a healthy fry up might work for you. Using turkey bacon, eggs, avocado and tomatoes as a replacement for starch will help lower your carbohydrate intake. 

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. You can also reduce the portion and/or try eating little but more often. 

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 hormone effect is wearing 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 fibre, protein and fat at these meals which act to slow down the absorption of carbohydrates.

However, if you do see spikes after these meals, the above advice is the same here. Choose lower GI options and lower your total carbohydrate intake. Make sure you replace the lost food with vegetable and protein options to prevent hunger.

Measuring between/before meals

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.

Whereas before meal readings demonstrate how well your body can lower its glucose levels after eating. This reading should ideally be below 6mmol/L. However, this assumes you haven’t eaten. If your reading is above 6mmol/L but below 7.8mmol/L but you have eaten carbohydrates between the meal then this is still fine as long as you aren’t then going above 7.8mmol/L later.

Difference between pre and post meal readings

One thing to take note of is the difference between your fasting or pre meal glucose level and your post meal glucose level. 

Obviously, if your pre meal glucose level is 7mmol/L, because you had some fruit as a snack, you only have a 0.8mmol/L margin before going high after the meal. 

On the other hand, if you chose a protein snack, like jerky for example and your glucose level before the meal is 5mmol/L, you now have a 2.8mmol/L margin at the meal before you have a high glucose level. In other words, you can eat more carbohydrate with the meal. 

Therefore, the difference can help provide more evidence about how the food at your meal has impacted your glucose levels. If you wake up with a glucose of 7mmol/L and rise to 7.9mmol/L after eating, this isn’t much of a glucose rise. Therefore, the high reading is due to waking up high in the first place. In all likelihood, your carbohydrate portion or choice was ok for you in this instance. 

However, if you woke up with a glucose level of 4.5mmol/L but saw a glucose rise to 9.5mmol/L after the meal, you can see this is a big difference. Therefore, your carbohydrate portion or the GI of that food, likely needs to be addressed. 

Summary of advice

It is good practice to try to combine a variety of foods groups at each meal. Therefore, a gestational diabetes diet still should be balanced and healthy.  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, jerkey, 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.


Exercise helps to lower glucose levels. This is because glucose is energy and by burning off more energy, you will help to lower your glucose levels. 

How much is enough depends on the individual. We know with pregnancy comes problems such as pelvic pain and discomfort. Therefore, the message with exercise is to do as much as possible but to tolerance. You know when you have over done it and therefore do not over exert yourself. 

Even walking for 10 minutes after meals can help lower glucose levels. Therefore, when it comes to gestational diabetes and exercise, every little helps. 

If you find your exercise levels drop off later into the pregnancy, you might find your glucose levels are higher than before. Don’t panic. It just means you may need to be more disciplined with your diet for the remainder of the pregnancy. 


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, the risk factors and your weight and lifestyle pre conception. These ultimately effect 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.

Need more help

If you need more support we offer a range of 1:1 consultancy services and online programmes focused on helping you improve your glucose control and health for the long term. These include our type 2 diabetes recovery programme, type 1 glucose stability programme and winning weight loss programme. Go to the pages using the links above or in the headers or get in touch if you have questions.