Starting low carb or keto with diabetes medications
So you have diabetes and you want to try a low-carb or keto diet? Congratulations! It may be the single best thing you could ever do for your health. It can start to reverse your type 2 diabetes, and dramatically improve your blood sugar control if you have type 1 diabetes.1
However, you need to know what you are doing. Once you start eating low carb you will likely have to lower your insulin doses, by quite a lot.2 Doses of some other types of diabetes medications may also need to be reduced.3
Avoiding the carbohydrates that raise your blood sugar level decreases your need for medication to lower it. Taking the same dose of insulin or insulin-stimulating oral medication as you did prior to adopting a low-carb diet might result in low blood sugar, something that can potentially become dangerous.
You need to test your blood sugar frequently when starting this diet and adjust your medication accordingly. This should ideally be done with the assistance of a physician or other health professional with expertise in diabetes (find a low-carb doctor).
Insulin-treated type 2 diabetes
As a general guide you will need to lower your doses when starting a strict low-carb diet.4
The reduction may need to be between 30 and 50%. If you take insulin once or twice daily, both doses should be reduced by the same proportion. If you are on a basal bolus regimen (taking fast-acting insulin before meals, and long-acting insulin once or twice a day), your mealtime doses should be reduced first.
If you remain low carb, it is possible you will be able to stop mealtime insulin altogether. You can then begin to reduce your long-acting insulin, if your blood sugar levels remain stable. Some people on a low carb diet are able to come off insulin completely. If you also take tablets for your diabetes, these should usually not be changed, until you have reduced your insulin as much as you are able to.
Unfortunately, there’s no way of knowing how much insulin is required in advance. You will have to test your blood sugar frequently and lower insulin doses based on your blood sugar readings. This should be done with the assistance of a knowledgeable physician.
Note that as a general rule, it is better to err on the low side of insulin doses. If your blood sugar goes a bit high you can take more insulin later to help bring it down. That’s OK. If instead you take too much insulin and end up having low sugar, that is potentially far more dangerous.
You’ll also have to quickly eat or drink glucose or another form of rapid-acting carbohydrate in order to raise your sugar to a safe level, and that obviously reduces the effect of the low-carb diet.
Insulin in type 1 diabetes
The above advice on insulin also applies to people with type 1 diabetes. A low-carb, high-fat diet can be fantastic for empowering people with type 1 diabetes to get steady blood sugars. It often results in much fewer and milder highs or hypos, as long as insulin doses are reduced appropriately.5
If you get regular hypos, you should consider reducing your insulin dosage before you reduce your carb intake. Most people with type 1 diabetes are treated with a basal bolus regimen, as described above.
Many people use an insulin to carbohydrate ratio (ICR) for their mealtime insulin. In this case, it is easy to manage a low carb diet as you continue to give the same ratio of insulin to the carbohydrates you eat. As you eat less carbohydrate, you will automatically inject less insulin.
In some cases, a higher ICR may be required due to the effect of protein increasing insulin requirements.6 Some people will lose weight with a low carb diet and become more insulin sensitive. If this occurs, it will be necessary to reduce the insulin to carbohydrate ratio, and possibly also the basal insulin doses.
People who use relatively fixed mealtime doses of insulin, or those on twice daily insulin, should use the same approach as those with type 2 diabetes. The difference is of course that people with type 1 diabetes will always need some insulin, even on a very low carbohydrate diet.
It is important to be aware that a diet with less than 50 grams of carbs each day can lead to ketosis. This is a normal physiological state that results from the body burning fat for energy.
A very strict low-carb diet that also restricts protein to moderate amounts can result in quite high, but still physiological (in other words, safe), ketone levels (e.g. 1.5 mmol/L, but sometimes as high as 4). This should not be confused with ketoacidosis, which is a dangerous complication of type 1 diabetes when there is insufficient insulin.
Ketosis is a normal response to using fat for energy. It is fine for healthy people, but in type 1 diabetes this means that you need to be sure you can differentiate ketosis from the much more dangerous ketoacidosis. The latter is associated with high blood sugar levels and dehydration, as well as high ketones.
We therefore recommend that when starting a low carb diet, a person with type 1 diabetes starts with a more liberal low-carb diet, with at least 50 grams of carbs a day. If you wish, you can then begin to reduce your carb intake to 30-40 grams of carbs per day as long as you have a high protein intake that will ensure you do not develop significant ketosis (>1.5 mmol/L).
Do not start a ketogenic low-carb diet (below 20 grams a day) unless you’re certain of how to handle this risk. If you do, test your ketones often, especially if you feel even slightly ill, practice intermittent fasting or have been exercising.7
It’s also important to remember that while people with type 2 diabetes can often reverse their disease enough to stop taking insulin injections entirely, someone with type 1 diabetes will always need to replace the insulin they lack.
With that said, a low-carb diet can have fantastic results for people with type 1 diabetes:
Some pills for type 2 diabetes work by stimulating the pancreas to produce more insulin. These medications can also result in low blood sugar on a low-carb diet.
These pills are either in the group known as sulfonylureas (this includes gliclazide, glipizide, glibenclamide, glyburide, and tolbutamide) or meglitinides (repaglinide and nateglinide).
You will need to reduce the dose or stop these drugs when starting a low-carb diet in order to avoid low blood sugar levels.8 We recommend this is discussed with your doctor in advance.
Metformin tablets can be safely taken on a low-carb diet. There is a very low risk of low blood sugar from taking Metformin.9
GLP-1 agonists (e.g. Victoza) and DPP-4 inhibitors (e.g. Januvia)
These drugs should rarely lead to low blood sugar on a low-carb diet by themselves.10 But be observant, check your blood sugar often, and discuss with your doctor as needed.
SGLT2 inhibitors (e.g. Farxiga, Jardiance, Invokana)
These drugs11 lower blood sugar in type 2 diabetes, and can be helpful in people on a more liberal low carb diet as they directly remove glucose (blood sugar) from the bloodstream. However, they can increase the risk of a dangerous condition called ketoacidosis.12
The risk of this could be increased by a strict low-carb diet.13 It is therefore advised to stop SGLT2 inhibitors before starting a strict low carb diet, and this should be discussed with your doctor.
It’s worth noting that when ketoacidosis occurs while taking SGLT2 inhibitors, the blood sugar level is not necessarily high, making it harder to detect.14
Type 2 diabetes:
Type 1 diabetes:
Asia Pacific Journal of Clinical Nutrition 2016: A randomised trial of the feasibility of a low carbohydrate diet vs standard carbohydrate counting in adults with type 1 diabetes taking body weight into account [moderate evidence]
This is true for people with type 1 diabetes as well as those with type 2 who take mealtime insulin.
How much your insulin dosage will need to be decreased depends on several factors, including carb intake and blood sugar control before starting a low-carb diet. Generally speaking, the lower your average blood sugars before you start eating low carb, the more insulin will need to be reduced when reducing your carb intake.
In one study, people with type 1 diabetes reported 82% less hypoglycemia at the one-year mark of following a low-carbohydrate diet providing about 75 grams of carbs per day:
Other studies have also shown that lower carb intake coupled with low insulin does can result in significantly fewer hypoglycemic episodes in those with type 1 diabetes:
Diabetes, Obesity and Metabolism 2017: Short-term effects of a low carbohydrate diet on glycaemic variables and cardiovascular risk markers in patients with type 1 diabetes: a randomized open-label crossover trial [moderate evidence]
Asia Pacific Journal of Clinical Nutrition 2016: A randomised trial of the feasibility of a low carbohydrate diet vs standard carbohydrate counting in adults with type 1 diabetes taking body weight into account [moderate evidence] ↩
All of these factors increase ketone production in the liver. In people who don’t have diabetes, the pancreas responds to rising ketone levels by releasing more insulin, which signals the liver to produce fewer ketones. Because this feedback loop is absent in those with type 1 diabetes, higher ketone levels may lead to diabetic ketoacidosis unless sufficient insulin is taken.
In low-carb studies, sulfonylurea medications often need to be discontinued within just a few days due to rapid improvement in blood sugar levels.
Nutrition and Diabetes 2017: Twelve-month outcomes of a randomized trial of a moderate-carbohydrate versus very low-carbohydrate diet in overweight adults with type 2 diabetes mellitus or prediabetes [moderate evidence]
Metformin improves insulin sensitivity and decreases the amount of sugar released by your liver but does not increase the amount of insulin released by your pancreas. Therefore, your blood sugar remains stable and doesn’t drop too low, no matter how few carbs you eat.
Unlike sulfonylureas, GLP-1 receptor agonists and DPP-4 inhibitors only lower blood sugar when it is elevated, resulting in very low risk of hypoglycemia.
The Journal of Clinical Endocrinology and Metabolism 2019: SGLT2 inhibitors increase the risk of diabetic ketoacidosis developing in the community and during hospital admission [weak evidence]
Low-carbohydrate diets have been identified as a contributing factor to diabetic ketoacidosis in those taking SGLT2 inhibitors.
Although relatively rare, diabetic ketoacidosis without elevated blood sugar (referred to as euglycemic DKA) has been found to occur in both people with type 1 and type 2 diabetes who take SGLT2 inhibitors.