Patients with type 1 diabetes are generally recommended to follow a low Glycaemic Index (GI), high carbohydrate diet, with carbohydrates comprising 45-65% of the daily calorie intake.¹ This is believed to help maintain glycaemic control while reducing the risk of cardiovascular disease in later life. However, low carbohydrate diets are becoming popular among some patients with type 1 diabetes, as a way to reduce insulin requirements, lower blood glucose levels, and aid weight loss.²

Low carbohydrate diets have been shown to be beneficial in type 2 diabetes, with meta-analysis data showing that low carbohydrate diets achieved higher rates of diabetes remission (defined as glycated haemoglobin [HbA1c] of <6.5%) than control diets. Additionally, low carbohydrate diets resulted in clinically important improvements in weight loss, insulin sensitivity and triglyceride levels.³ But are low carbohydrate diets beneficial in type 1 diabetes? Here’s what the evidence shows.

Low Carbohydrate Diets in Type 1 Diabetes: The Evidence

Large-scale randomised controlled trials on low carbohydrate diets in type 1 diabetes are lacking; however, a number of observational and open-label clinical trials have been conducted in adults and adolescents with type 1 diabetes. While some outcomes differed, all of these trials demonstrated significant improvements in glycaemic control, with significant reductions in HbA1c levels, and increased time spent in the ideal range for blood glucose.^4-9

Is it Safe?

Hypoglycaemia and Diabetic Ketoacidosis

One of the concerns raised around low carbohydrate diets for type 1 diabetics is that it may increase the risk of serious hypoglycaemic episodes and diabetic ketoacidosis.² One observational study found that patients on a low carbohydrate diet had an incidence of 0.9 hypoglycaemic episodes per day.⁴ As this was an uncontrolled study, it is not known how this incidence compares to similar patients following a higher carbohydrate diet; however it has been described as a high incidence.¹⁰  Of the remaining trials, two observed no significant difference in hypoglycaemic episodes compared to controls,^5,8 while two studies reported a reduced frequency of hypoglycaemia in those following the low carbohydrate diet.^6,7 Hypoglycaemic episodes reduced by 75% in one study after 6 months on the low carbohydrate diet.⁷ The remaining study did not specifically report on incidence of hypoglycaemic episodes.⁹ There were no episodes of diabetic ketoacidosis reported in these studies. Several studies did report reduced insulin requirements with a low carbohydrate diet, so dose adjustments are necessary to maintain healthy blood glucose levels.^5-7

Nutritional Status

Type 1 diabetes mainly affects children and adolescents, who may be at greater risk of nutritional deficiency with restricted diets.² One study conducted in type 1 diabetic adolescents did show a reduced intake, below the recommended daily amount, of several nutrients, including iron, folate, vitamin B1, and calcium, after 6 months on a low carbohydrate diet.⁹ Further studies in children with type 1 diabetes are lacking. However, a systematic review on the safety of low carbohydrate and ketogenic diets in children with refractory epilepsy reported mixed findings on bone heath and growth patterns, with some studies reporting no changes and others reporting negative effects. However, studies that included vitamin and mineral supplementation alongside the low carbohydrate diet found no adverse effects on bone health or growth.¹¹

Cardiovascular Health

Concerns have been raised about the effects of a higher fat diet such as ketogenic or low carbohydrate diet on cardiovascular health.² Of the studies conducted in type 1 diabetics, effects on cardiovascular risk factors were variable. One uncontrolled observational study reported that serum lipid levels were above the recommended range in the majority of patients on a low carbohydrate diet.⁴ Four studies found no significant changes in lipid profiles,^5,6,8,9 while one reported significant improvements in blood lipids on the low carbohydrate diet.⁷ Two studies also reported no changes in blood pressure, and another reported reduced C-reactive protein (CRP) levels.⁹ In support of these findings, a Cochrane review found that there were no significant changes in cardiovascular risk factors associated with a low carbohydrate diet over two years.¹²

What’s The Verdict?

There are not enough high-quality, large-scale studies to give a definitive recommendation; however, these preliminary results are very promising in support of a low carbohydrate diet. Diabetes Australia states that there is no perfect, one-size-fits-all diet for type 1 diabetes, and advises that the best diet is the one that works for the individual patient. If patients wish to try a low carbohydrate or ketogenic diet, they should be supported to do so, and offered appropriate guidance on how to do so safely.² To reduce the risk of serious hypoglycaemic episodes or diabetic ketoacidosis, extra close monitoring of blood glucose levels is required, with continuous glucose monitoring ideal.¹⁰ Appropriate dose adjustment of insulin is required, with patients advised by experts to err on the side of avoiding hypoglycaemia rather than hyperglycaemia. One review recommended an initial basal insulin dose reduction of 10-20%, which should be adjusted weekly; however any medication adjustments must be discussed by the patient with their diabetes medical team.¹⁰ Diabetes Australia advises that a low carbohydrate diet should not be recommended for anyone with increased nutritional demands, such as children, and pregnant or breastfeeding women. However, they acknowledge that individual assessment is required.² If a reduced carbohydrate diet is being utilised in these patient groups, a high-quality multivitamin and mineral supplement seems pertinent to reduce the risk of nutritional deficiencies impacting growth and development.¹¹ Periodic monitoring of blood lipids and blood pressure also seems like a sensible step.

The Bottom Line

As is so common in the field of healthcare, there is no simple answer to suit all patients. It is vital to assess the needs and requirements of the individual sitting in front of you. However, the available evidence suggests that, with appropriate guidance and monitoring, a low carbohydrate or ketogenic diet can be highly beneficial for individuals with type 1 diabetes.

References

¹ Australian Type 1 Diabetes Guidelines Expert Advisory Group. National evidence‐based clinical care

guidelines for type 1 diabetes in children, adolescents and adults [Internet]. Canberra; Australian Government Department of Health and Ageing. 2011. [Cited 10 July 2024]. Available from: https://www.diabetessociety.com.au/documents/Type1guidelines14Nov2011.pdf

² Diabetes Australia. Low carbohydrate eating for people with diabetes [Internet]. Canberra; Diabetes Australia. 2018 [cited 10 July 2024]. Available from: https://www.diabetesaustralia.com.au/wp-content/uploads/Diabetes-Australia-Position-Statement-Low-Carb-Eating.pdf

³ Goldenberg JZ, Day A, Brinkworth GD, Sato J, Yamada S, Jönsson T, et al. Efficacy and safety of low and very low carbohydrate diets for type 2 diabetes remission: systematic review and meta-analysis of published and unpublished randomized trial data. BMJ. 2021 Jan 13;372:m4743.

⁴ Leow ZZX, Guelfi KJ, Davis EA, Jones TW, Fournier PA. The glycaemic benefits of a very‐low‐carbohydrate ketogenic diet in adults with Type 1 diabetes mellitus may be opposed by increased hypoglycaemia risk and dyslipidaemia. Diabet Med. 2018 Sep;35(9):1258-63.

⁵ Krebs JD, Parry Strong A, Cresswell P, Reynolds AN, Hanna A, Haeusler S. 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. Asia Pac J Clin Nutr. 2016;25(1):78-84.

⁶ Ranjan A, Schmidt S, Damm‐Frydenberg C, Holst JJ, Madsbad S, Nørgaard K. 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. Diabetes Obesity Metabolism. 2017 Oct;19(10):1479-84. DOI:10.1111/dom.12953

⁷ Shaker Mahmood B. Impact of low carbohydrate diet on patients with type 1 Diabetes. E3S Web Conf. 2023;391:01132. DOI:10.1051/e3sconf/202339101132

⁸ Sterner Isaksson S, Ólafsdóttir AF, Ivarsson S, Imberg H, Toft E, Hallström S, et al. The effect of carbohydrate intake on glycaemic control in individuals with type 1 diabetes: a randomised, open-label, crossover trial. The Lancet Regional Health - Europe. 2024 Feb;37:100799. DOI:10.1016/j.lanepe.2023.100799

⁹ Levran N, Levek N, Sher B, Gruber N, Afek A, Monsonego-Ornan E, et al. The Impact of a Low-Carbohydrate Diet on Micronutrient Intake and Status in Adolescents with Type 1 Diabetes. Nutrients. 2023 Mar 15;15(6):1418. DOI:10.3390/nu15061418

¹⁰ Buehler LA, Noe D, Knapp S, Isaacs D, Pantalone KM. Ketogenic diets in the management of type 1 diabetes: Safe or safety concern?. CCJM. 2021 Oct;88(10):547-55. DOI:10.3949/ccjm.88a.20121

¹¹ Wells J, Swaminathan A, Paseka J, Hanson C. Efficacy and Safety of a Ketogenic Diet in Children and Adolescents with Refractory Epilepsy—A Review. Nutrients. 2020 Jun 17;12(6):1809. DOI:10.3390/nu12061809

¹² Naude CE, Brand A, Schoonees A, Nguyen KA, Chaplin M, Volmink J. Low-carbohydrate versus balanced-carbohydrate diets for reducing weight and cardiovascular risk. Cochrane Database of Systematic Reviews. 2022 Jan 28;2022(1):1. DOI:10.1002/14651858.CD013334.pub2