Starting low carb or keto with diabetes medications

By Dr. Andreas Eenfeldt, MD – Updated February 22, 2019

 
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 increase your blood sugar control with type 1 diabetes.

However, you need to know what you are doing. Once you start eating low carb you may instantly have to lower any insulin doses, a lot.

Avoiding the carbohydrates that raise your blood sugar decreases your need for medication to lower it. Taking the same dose of insulin 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 adapt (lower) your medication. This should ideally be done with the assistance of a knowledgeable physician.

No drugs

If you have diabetes and you’re treated either by diet alone or just with Metformin there is very low risk from low blood sugar on low carb. You can get started right away.

Insulin

As a general guide you may need to lower your doses by 30-50% or more when starting a strict low-carb diet.

Unfortunately there’s no way to know the doses required in advance. You’ll have to test your blood sugar frequently and adapt (lower) insulin doses. This should be done with the assistance of a knowledgeable physician.

Note that as a general rule it’s easier to err on the low side, and if your blood glucose goes a bit high you can take more insulin later if needed. That’s OK. If instead you overdose and get low sugar that is potentially far more dangerous. You’ll also have to quickly eat or drink more carbohydrates, and that obviously reduces the effect of the low-carb diet.

Insulin in type 1 diabetes

The advice on insulin above generally applies to type 1 diabetes too. A low-carb, high-fat diet can be fantastic for empowering people with type 1 diabetes to get steady blood sugars. It results in much fewer and milder highs or hypos (when insulin doses are adapted).

If you get regular hypos you should consider lowering your insulin.

One word of warning though: A strict low carb diet results in ketosis, a normal physiological state. 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 is fine for healthy people, but in type 1 diabetes this means you’re uncomfortably close to ketoacidosis (usually at least 10-15 mmol/L). All that’s needed then is forgetting an insulin shot or two, or an insulin pump malfunction, and you might end up very sick in the hospital.

Thus it’s probably best in type 1 diabetes to try a more moderate low-carb diet, with a minimum of around 50 grams of carbs a day, so that you stay out of deeper ketosis (>1.5 mmol/L).

Do not do a strict low-carb diet (below 20 grams a day) unless you’re certain of how to handle this risk. Adding for example a fruit or two a day to it is probably wise, if you have type 1 diabetes. Just to be safe.

It’s also important to remember that while people with type 2 diabetes can relatively 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:

Insulin-releasing pills

Some pills for type 2 diabetes work by releasing more insulin in the pancreas. These can also result in low blood sugar on a low-carb diet, even if the risk is slightly smaller than with injected insulin.

These pills are called sulfonylureas and include glipizide, glibenclamide and glyburide, etc.

You may need to reduce the dose or stop these drugs on a low-carb diet, as you may rapidly become too healthy for them. Discuss it with your doctor in advance.

Metformin

Metformin tablets can be safely taken on a low-carb diet. There’s a very low risk of low blood sugar if you’re only on Metformin.

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. But be observant, check your blood sugar often and discuss it with your doctor as needed.

 

SGLT2 inhibitors (e.g. Farxiga, Jardiance, Invokana)

These drugs¹ are a good way to treat type 2 diabetes, but as a known side effect they increase the risk of a dangerous condition called ketoacidosis. It’s likely that this side effect could become more common on a strict low-carb diet. Proceed with caution and discuss it with your doctor.

It’s worth noting that when ketoacidosis occurs while taking SGLT2 inhibitors, blood glucose is not necessarily high, making it harder to detect.

If you get symptoms of ketoacidosis: extreme thirst, nausea, vomiting, stomach pain, confusion etc. you should stop the medication, eat carbs and contact a doctor immediately.

Learn more

How to reverse type 2 diabetes

More

A low-carb diet for beginners

A keto (strict low-carb) diet for beginners

Low carb for doctors

Are you a doctor or do you know one? Here’s our low carb for doctors resource, with information on how to safely handle medications on a low-carb diet:

Low carb for doctors