Are Low Carb Diets Dangerous for T1D?

You should know the benefits and risks of low-carbohydrate / ketogenic diets for people with type 1 diabetes

The Keto Diet is perhaps the hottest trend in eating styles for diabetes and can be effective in losing weight. It is not without controversy, however, because eating a low/no carb diet will induce ketosis in any person.

For a person with T1D, it is important to understand the difference between nutritional ketosis and ketoacidosis – ketoacidosis (DKA) is a life-threatening condition caused by inadequate insulin.

Your need for insulin may decline on a low-carb diet but reducing your doses should be done with care.  DKA may be more likely to occur when insulin needs are higher, such as during an illness, periods of high stress, corticosteroid use, heart attack, and drug abuse. It can also occur when insulin doses are missed or if an insulin pump stops working. DKA risk can be further compounded by medications you may be taking in addition to insulin, specifically SGLT2 inhibitors.

Benefits of a low-carbohydrate diet

There is research that following a low carbohydrate diet will somewhat improve glucose control, both A1C and glucose variability. With any change in diet, insulin adjustments must be made. Most studies show that participants who adhere to a low-carbohydrate diet significantly reduce insulin requirements. This makes sense – less carbohydrate intake results in less insulin needed to handle the influx of glucose from food into the bloodstream.

If dosing using an insulin-to-carb ratio, however, it is important to monitor blood sugars after meals, as you may find that high protein, no carbohydrate meals DO require some insulin to keep post-prandial numbers in check. This is a strategy that needs to be individualized based on your own experience and observations.

The downsides of a low-carb diet

There are other factors that make low-carbohydrate diets tricky to manage.  

A very low carbohydrate diet could cause weight and growth decline in children, which is likely related to reduced palatability of the diet.

  • Children with T1D  are twice as likely to receive a psychiatric diagnosis, including eating disorders.
  • Low carbohydrate diets can also cause fatigue, especially during the first few months as the body adapts to using ketones as a fuel source. Therefore, adopting restrictive eating behaviors could be a precursor to disordered eating and contribute to social isolation.
  • Based on the research available, recommending a low carbohydrate diet or ketogenic diet for blood glucose control in children with T1D is NOT advised.

A major worry for health care providers when recommending a low carbohydrate diet is the potential for negative effects on cholesterol levels.  

  • Multiple studies, in populations with and without T1D, show a significant increase in unhealthy (LDL) cholesterol when following a low carbohydrate diet.
  • This is likely related to the high saturated fat intake that is typical of these diets.
  • Saturated fat increases LDL, a major risk factor for atherosclerosis and cardiovascular disease (CVD).

Replacing saturated fat with mono- or polyunsaturated fat decreases LDL and triglycerides and is associated with lower rates of CVD and death.

Therefore, the quality of fat is of the utmost importance. There is also a concern for micronutrient and electrolyte deficiencies (sodium, potassium, magnesium, calcium) when following a ketogenic or low carbohydrate diet.

Additional concerns to think about

Three other factors should be considered with low carbohydrate or ketogenic diets.

  • Glucagon injections may be less effective when following a low-carb diet. This is because carbohydrate intake is so low that glycogen stores are in a depleted state. Therefore, the glucagon does not have as much glycogen to breakdown to turn into glucose. It has been shown in research that shorter-term low carb diets do elicit a reduced glucose response to glucagon rescue. To my knowledge, glucagon recovery response has not been studied in people that have type 1 diabetes who have been following a low-carb diet (<50g/day) long-term aka Keto-adapted. This could potentially cause adaptations to glycogen that would yield a different response (perhaps a more effective one) when glucagon is used as an emergency remedy treatment.
  • People taking SGLT2 inhibitor drugs (Jardiance, Invokana, Farxiga, Steglatro) are likely at higher risk for ketoacidosis if following a low carbohydrate diet. Therefore, it is not advised to follow such a diet when taking an SGLT2 inhibitor medication. For detailed information, see this IN article.
  • Very high-intensity exercise may not be attainable on a low carbohydrate diet. When exercising at extremely high intensity, the body is reliant on carbohydrates as a fuel source. Therefore, you may notice a decline in performance when doing this specific type of physical activity.


  • You may need to adjust carbohydrate intake to match your needs for exercise.
  • Combining low-carb diets with SGLT2 inhibitor drugs increases your DKA risk and should not be done without very careful healthcare guidance.
  • Understanding how to adjust your insulin to prevent hypoglycemia when following a low carbohydrate diet is of the utmost importance.
  • The quality of dietary fat is key when planning a low carbohydrate diet.  It is recommended that you discuss your new diet with your physician and check your cholesterol levels regularly to ensure your new diet is not having a negative effect.

Reader Comment

I just read through the keto diet for DM1 article, and while I agree there are actual concerns with the diet, I just wanted to point out one glaring inaccuracy. The author states that glycogen is depleted on a low carb diet, but that is simply not true. Here is a link looking at multiple parameters in endurance athletes, low carb and high carb, One of the main takeaways is that resting and post 3hr run glycogen levels are not statistically different. While it looks like you have someone who is an “expert” on DM1 and nutrition based on her credentials and current work, it appears she is not up to date on all aspects as this paper is from 2016, or maybe it is just personal bias. Also, she apparently intentionally simplifies the role of LDL in the parthenogenesis of atherosclerotic cardiovascular disease by leaving out particle size importance and the role of triglycerides, without investigating how these parameters change with diet, and they do in a positive fashion, small LDLs down and trigs down with low carb eating. Whereas she only reports that LDL increases on low carb. This is nuanced because LDL has a variable response to low carb diets, some people actually go down.

Author Response

Thank you for your comments. I am quite up to date on the literature and I am familiar with Dr. Volek and Dr. Phinney’s work. I actually wanted to include particle size in the article but this specific article was created for the lay-reader in mind. When I present on this topic I always include data and discussion on particle size. Perhaps it should have been included here too.

Here is some interesting information on particle size.

McDonald, et al. — — Impact of a modified Atkins diet on cardiovascular health in adults with epilepsy. Epilepsy & Behavior. 2018; 79: 82-86

That study showed an increase in small dense LDL with patients following a low carb diet long term. Increased concentrations of small dense LDL are one of the most frequent dyslipidemias found in patients with premature CAD and may be predictive of MI risk. However, these patients did not exhibit an increase in plaque. The authors suggest that longer-term studies would prove useful for better understanding of this phenomenon. They also suggest that it is safe to follow such a diet, but lipids should be closely monitored when using a low-carb diet for long term therapy. In addition, please refer to the American Heart Association Presidential Advisory on Dietary Fats and Cardiovascular Disease (2017), which further highlights the role of various types of fats on CVD.

The most important thing to keep in mind is that a low-carb diet will likely affect each individual very differently with regards to cardiovascular risk. This is why I suggested close follow up with one’s physician to look at CVD risk factors when a large dietary change such as this one is made. In this study from Leow ZZX et al. you can see an example of how a high saturated fat, low-carb diet in persons with T1D can negatively affect one’s lipids:— The glycaemic benefits of a very-low-carbohydrate ketogenic diet in adults with Type 1 diabetes mellitus may be opposed by increased hypoglycemia risk and dyslipidemia. Diabetes Med. 2018. May 8 DOI: 10.1111/dme.13663

Here is information on glucagon effectiveness.

Ranjan A., et al. — — Low-Carbohydrate Diet Impairs the Effect of Glucagon in the Treatment of Insulin-Induced Mild Hypoglycemia: A Randomized Crossover Study.

This study done in Type 1 patients makes it very clear that if a patient starts on a low-carb diet (<50d/day) it will reduce glucagon effectiveness.

In regards to the Volek et al. study, I do agree that there are interesting phenomena that occur with Keto-adapted athletes, like the one you refer to at 120 minutes post-exercise with these 10 athletes. However, we don’t have any studies like the Rajan et al. one looking at glucagon effectiveness in Keto-adapted athletes. That would be awesome to see!

Nicole Rubenstein is a Registered Dietitian, Board Certified Sports Dietitian and Certified Diabetes Educator. She owns Racer’s Edge Nutrition, a sports nutrition private practice specializing in athletes with diabetes. She is also the lead dietitian in the Endocrinology and Weight Management Departments at Kaiser Permanente in Denver, CO. She completed her undergraduate degree in Nutritional Science from Cornell University and her Master’s Degree in Sports Nutrition at the University of Colorado in Colorado Springs. Prior to her studies, Nicole was a competitive snowboard athlete and travelled the world competing in snowboard racing. She now enjoys snowboarding, mountain biking, scuba diving, cooking, and spending time with her husband and two dogs. Nicole has spent the last 12 years helping patients improve their health through bettering their nutrition habits. Of all the specialties that she has worked with, her primary passion is working with active individuals who have type 1 diabetes.

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