When you digest food and drink, carbohydrates are broken down into glucose. The glucose passes into your blood and is either stored or used by the body for energy. It is important to have enough glucose in your blood to provide energy for your body to work properly.
If you have diabetes caused by pancreatic cancer (type 3c diabetes), your blood sugar (glucose) levels may become too high or too low. Blood sugar level is measured in units of millimole per litre – shortened to mmol/l.
Your pancreas normally makes hormones called insulin and glucagon which keep your blood sugar at the right level. Pancreatic cancer can stop your pancreas making enough of these hormones. This can cause type 3c diabetes, which means your blood sugar levels may become too high or too low.
High blood sugar levels can make you more likely to lose weight, feel more tired, thirsty and have problems concentrating. In the long term, high blood sugar levels can damage your heart, eyes, feet and kidneys.
High blood sugar levels can also increase the risk and severity of infections like colds, thrush, wound infections and urine infections. So it’s important that your blood sugar level is properly managed if you are having chemotherapy or surgery.
A low blood sugar level of less than 4mmol/l is called hypoglycaemia, or a hypo. This needs to be treated quickly. A hypo can cause seizures or loss of consciousness if it’s not treated.
Most people with type 3c diabetes will need to monitor their blood sugar level. There are different ways to do this.
If you need to check your blood sugar level regularly, you may be given a blood sugar monitor. Your diabetes nurse will show you how to use it.
You will need to prick your finger to produce a small drop of blood, which you put onto a measuring strip in the monitor. The monitor tells you what your blood sugar level is within a few seconds.
Some people who take insulin use these monitors. A sensor is attached to your arm, with the tip just under your skin. This constantly measures the glucose in the fluid around the cells under the skin (interstitial fluid). The reading is sent to an app on a mobile phone or a reading device.
Using a flash monitor or CGM means that you can easily check your glucose levels at any time, without pricking your finger. The devices have alarms that can be set to alert you if your glucose levels are too high or too low (hypoglycaemia).
Speak to your diabetes team about whether a flash monitor or CGM might be suitable for you. Some people can get a monitor for free on the NHS, so ask your team if you would be eligible. You can buy the monitors privately, but they are quite expensive.
Some people don’t need to check their blood sugar levels regularly, so won’t need a monitor. Your doctor or nurse will do blood tests to check your blood sugar levels.
They may do a random blood glucose test which tells you what your blood glucose level is at that moment. Or they may do an HbA1c test, which shows what your blood glucose level has been on average over the past 12 weeks. Your doctor or nurse may also ask you about any symptoms you have.
Diabetes UK has more information about testing your blood sugar levels.
There is an ideal range for blood sugar levels called the target range. The target range will be specific to you. It may depend on lots of things, including your cancer and treatment, your weight, and how well you are. It may change over time.
If you have lost weight, maintaining or putting on weight is important. The aim will be to manage the diabetes around your diet.
Speak to your diabetes team about your target range.
If you have type 3c diabetes, it can be hard to get your blood sugar level into your target range. Most people will need tablets or insulin to do this.
Read more about how diabetes is treated.
The diabetes team will explain how to take your diabetes medicine and help you manage the diabetes. It usually takes a few weeks for your blood sugar levels to get into range once you start treatment.
Blood sugar levels are affected by many things, including:
If you are eating less because you feel sick or are being sick, or don’t have much appetite, this can affect blood sugar levels. Pancreatic cancer and treatments can cause sickness and reduced appetite. You may need to monitor your blood sugar levels more often. Your diabetes team can help you manage your blood sugar levels if you are eating less.
Some chemotherapy drugs are mixed in sugary liquids. Your oncology team should take your diabetes into account when giving chemotherapy and should monitor your blood sugar levels. Some people find it harder to eat for a few days after having chemotherapy. You may also be sick or have diarrhoea. This can also affect your blood sugar levels.
If you are having chemotherapy, it’s a good idea to monitor your blood sugar levels and let your medical team know if these are higher or lower than normal.
Steroids are sometimes given with chemotherapy or may be used to treat some symptoms like sickness. Steroids can make your blood sugar levels rise. Talk to your diabetes nurse about managing your blood sugar levels if you are having steroids.
Different foods and drinks can affect your blood sugar levels. If you have type 3c diabetes, you should not try to manage your diabetes by reducing how much carbohydrate you have.
If you can, eat regularly and don’t skip meals. You may also need to take pancreatic enzymes when you eat, so that you are able to digest your food and absorb the nutrients from it.
Speak to your diabetes team if your blood sugar levels are often above or below your target range. Don’t change or reduce what you eat to bring your blood sugar levels down unless this has been recommended by your diabetes team or dietitian. Changing what you eat could reduce the nutrition your body gets. Only change your diabetes medicine if your diabetes team tell you to.
There is a lot of information online about changing your diet if you have diabetes – but this is mainly for people with other types of diabetes. This advice may not be right for you if you have type 3c diabetes.
Read more about the difference between type 3c diabetes and type 1 and type 2 diabetes.
“It was made clear to me that with the correct insulin and Creon® I could eat what I wanted.”
Most people are told to avoid drinking sugary drinks outside of mealtimes as they can cause a big rise in your blood sugar level. This can make you feel less well, and it can be hard to bring the blood sugar level back down. But if you are unwell and can’t eat, you may be advised to have sugary drinks.
If you have lost weight or strength or are struggling to maintain your weight, you may need more calories and protein in your diet to help you gain weight and strength. It may include having foods or nutritional supplements that increase your blood sugar level. Your diabetes will need to be managed around this. You may need more medicine to keep within your target range.
Don’t avoid foods or reduce how much you eat, unless your dietitian tells you to, as this will stop you getting the nutrition you need.
Speak to your dietitian about how to put on weight if you have diabetes. Tell them if your blood sugar levels are high. They may suggest changes to your medicine.
Carbohydrates include starchy and sugary foods (see below). When you eat, carbohydrates are broken down into glucose. This is absorbed into the blood and makes your blood sugar levels rise.
Starchy carbohydrates are an important source of energy and a key part of a healthy diet. It’s important that you eat food containing starchy carbohydrate.
Regular portions of starchy carbohydrates help to keep your blood sugar level constant. This is because the glucose is released more slowly from these foods than from sugary carbohydrates. Be aware that food and drinks that have a lot of sugar but not much protein, fibre or fat can cause sudden peaks in your blood sugar.
Starchy foods include:
Foods containing both starch and sugar include:
Sugary foods include:
Fruit, milk and yoghurt all contain sugar. But these are different to the sugar in sweets and sugary drinks and they have less effect on blood sugar levels. Fruit, milk and yoghurt also contain other important nutrients and can be eaten often as part of a healthy diet.
Speak to your dietitian if you would like more information about eating food containing carbohydrates.
You don’t need to avoid sugar if you have type 3c diabetes – it can be part of a balanced diet. But a lot of sugar in your diet does make it harder to keep your blood sugar levels within your target range.
You can use sweeteners instead of sugar and choose ‘no added sugar’ options if you want to reduce the amount of sugar you have. Some sweeteners may cause diarrhoea (runny poo), and you should avoid these. Check the brands with your dietitian. ‘Diet’ versions of sugary drinks won’t affect blood sugar levels.
Diabetic foods aren’t recommended. They are expensive and can also cause diarrhoea if you have a lot of them.
These foods should not make your blood sugar levels rise or drop:
Although these foods may not affect your blood sugar levels, most contain proteins and fats, so you will still need to take pancreatic enzymes when you eat them.
Hypoglycaemia or a ‘hypo’ is a low blood sugar level of less than 4mmol/l. Some people find it helpful to remember ‘four is the floor’, so not to go below this. If untreated, a hypo can cause seizures or loss of consciousness. It needs to be treated promptly.
A hypo can be caused by:
Some treatments for diabetes increase how much insulin your pancreas makes. These include gliclazide and glimepiride. If the dose of these is too high, this can also cause a hypo.
Symptoms of a hypo include:
There are two steps to treating hypoglycaemia. You must follow both steps to properly treat the hypo. It might be useful to share this information with the people you spend time with, particularly if you have recently been diagnosed with diabetes or if you don’t always recognise the symptoms of a hypo.
Step 1: Straight away, take 15-20g of fast acting carbohydrate (sugar). For example:
Milk, foods with fat (like chocolate) or sugar added to drinks are not effective at this stage, as they won’t increase your blood sugar level fast enough.
Wait 10-15 minutes and check your blood sugar level again. If it remains low (below 4mmol/l) repeat step 1. If it has come back to the target range (above 4mmol/l) then go to step 2.
If you have repeated step 1 three times and your blood sugar level is still below 4mmol/l, phone 999 for an ambulance.
Step 2: Eat 15-20g of starchy carbohydrate. This causes a gradual rise in your blood sugar level and can help to keep your sugar level steady after a hypo.
This could be:
• half a sandwich
• 2 plain digestive biscuits or 3 rich tea biscuits
• a medium banana
• a small bowl of cereal
• 1 medium or thick slice of toast
• a 300ml glass of milk
• or your next meal, if it’s due.
Read more about foods containing carbohydrate.
If you take pancreatic enzymes, don’t forget to take these with step 2 of your hypo treatment. You don’t need enzymes with step 1.
Always keep something to treat a hypo with you when you are out and about. If you drive, keep something in the car. Read more about driving and diabetes.
You should also keep your testing kit and something to treat a hypo by your bed in case you have a hypo overnight. If you have type 3c diabetes, your pancreas doesn’t produce enough glucagon and that can make night time hypos more likely. Night time hypos are also more likely if you:
If any of these have happened, you may need a bedtime carbohydrate snack to reduce the risk of a hypo. It is important that you don’t inject insulin with this snack as this could cause your blood glucose levels to drop too low. Do take your pancreatic enzymes with the snack though.
If you have regular hypos, speak to your diabetes team. It’s likely that your diabetes medicine will need to be changed.
We have listed some of the references to the sources used to write this information. If you would like the full list of references, email us at publications@pancreaticcancer.org.uk
Updated June 2026
Review date June 2029
