Volume 23, Number 1 - April 2020

Low carbohydrate diets and diabetes

By
Kate Marsh

BSc, MNutrDiet, PhD, Grad Cert Diab Edn & Mgt

Advanced Accredited Practising Dietitian & Credentialled Diabetes Educator

Northside Nutrition & Dietetics (NSW)

editor@adea.com.au

Kate is a CDE and Advanced APD and is the current editor of the Australian Diabetes Educator (ADE) and Chair of the Editorial Advisory Group (EAG). She is a Fellow of the ADEA and the Australasian Society of Lifestyle Medicine (ASLM).

Kate currently divides her time between clinical practice and health and medical writing, and has a private practice in Sydney where she works mostly with individuals with diabetes and women with PCOS (who are at high risk of developing GDM and T2 diabetes).

Kate has been a member of the EAG since 2005 and chair since 2015. She is also a long-time editorial board member for Diabetes Management Journal (DMJ) and a board member of ASLM. Kate writes regularly for Diabetic Living magazine and the limbic Diabetes Educator/Endocrinology. She also works as a freelance writer for Diabetes Australia.

Kate has published articles in a number of other consumer publications and medical journals, written four consumer books and has contributed the dietary chapters to several textbooks on the topics of diabetes, vegetarian and plant-based diets, PCOS, insulin resistance, glycemic index and pregnancy.  She also speaks regularly on these topics to both health professionals and consumers and is a guest lecturer on PCOS at The University of Sydney.

Kate is a member of the Guideline Development Group for the PCOS International Evidence-Based Guidelines and the PCOS Centre for Research Excellence (CRE) Translation Committee.  She was also a member of the working parties developing the current evidence-based guidelines for the diagnosis and management of PCOS and type 1 diabetes in Australia

Kate is a recipient of the DAA Young Achievers Award, was a NSW finalist in the 2006 Telstra Business Women’s Awards, and was awarded the DAA Joan Woodhill Prize for Excellent in Research – Doctorate Award for her PhD study on low GI diets for women with PCOS. In 2015 she was awarded the inaugural ADEA Jan Baldwin National CDE of the Year.

Introduction

Low carbohydrate diets, including low carbohydrate high fat (LCHF) and ketogenic (keto) diets have been gaining popularity in the general population, particularly for weight loss, but also in people with diabetes, as a way of managing blood glucose levels.  However, there is confusion amongst both people with diabetes and health professionals about the suitability of these diets.  This article aims to provide an overview of the current research on low carbohydrate diets and diabetes, to help diabetes educators to understand the benefits and risks of this dietary approach, along with important considerations for people with diabetes who choose to adopt a lower carbohydrate eating plan.

What is a low carbohydrate diet?

There is no standard definition of ‘low carbohydrate’ used in research.  The term low carbohydrate has been used to describe diets as low as 20g of carbs per day or for those with a more modest reduction in carbs (less than 45% of total energy intake).  However, Feinman et al. have proposed definitions for different levels of carbohydrate restriction to be used in research, outlined in Table 1.

Table 1: Definition of a low carbohydrate diet

Description CHO intake (grams/day) CHO intake (% total energy)
Very low carbohydrate ketogenic diet 20-50g/day <10%
Low carbohydrate diet <130g/day <26%
Moderate carbohydrate diet 26-45%
High carbohydrate diet >45%

In practice, low carbohydrate and very low carbohydrate diets restrict or exclude a wide range of foods including wholegrains, starchy vegetables, legumes, most fruits and some dairy foods, replacing them with non-starchy vegetables, meat, poultry, seafood, eggs, olive oil, coconut oil, nuts, and dairy foods such as cheese, butter, cream and Greek yoghurt.  They often encourage choosing higher fat cuts of meat and full-fat dairy foods.

Are we really eating too many carbs?

Advocates of low carbohydrate diets say that eating too much carbohydrate is contributing to our increasing waistlines and development of chronic disease, including diabetes. However, evidence doesn’t support these claims.

Current government guidelines recommend a carbohydrate intake between 45 and 65% of energy, coming predominantly from low energy density and/or low glycaemic index foods1.  This range is based on meeting requirements for micronutrients (vitamins and minerals) as well as fat and protein needs. In the 2011-2012 Australian Health Survey the average Australian adult was consuming only 43.5% of energy as carbohydrate, below the lower end of this range2.

Furthermore, at the time of the survey, only 30% of Australians were eating the recommended serving of non-discretionary grains, 31% the recommended servings of fruit and less than 4% were meeting the recommended serves of vegetables and legumes3.  Only one-third of grain foods consumed were wholegrain or high fibre products, compared to the recommended two-thirds. Instead the average Australian consumed 35% of their energy from ‘discretionary’ foods (foods which are energy-dense but provide little nutritional value)4.  While we are still awaiting additional findings from the more recent 2017-2018 National Health Survey, data on fruit and vegetable consumption show similarly low intakes to the previous survey5.  So, it seems that our problem is not that we are eating too many carbs but that we are choosing less healthy options.

What does the research say about low carbohydrate diets and diabetes?

Most of the research on the use of low carbohydrate diets in diabetes management has been conducted in people with type 2 diabetes (T2D) and several systematic reviews and meta-analyses have been published over the past few years. The authors of these reviews have come to similar conclusions: that while lower carbohydrate diets may result in improvements in glycaemic management in the short-term (3-6 months), they don’t appear to be significantly better than higher carbohydrate diets in the longer-term (12 months or more)6–8. Some studies show greater short-term improvements in glycaemic markers with lower carbohydrate intakes6–8.  However, research also suggests that very low carbohydrate diets are difficult to sustain, an important consideration when making dietary recommendations7.

Furthermore, similar benefits (including weight loss, improvements in glycaemic management and cardiovascular risk factors, and reductions in medication use in T2D) have been achieved with other dietary patterns, including Mediterranean, vegetarian and vegan diets, the latter two typically high in carbohydrate and lower in fat9, 10.  This suggests that while carbohydrate restriction may be one option for the dietary management of T2D, it is not the only option, nor is it necessary for optimising glycaemic management or achieving weight loss.

There is currently limited evidence to support the efficacy and safety of low carbohydrate diets in individuals with type 1 diabetes (T1D). While there is some evidence to show lower HbA1c levels and reduced insulin needs in those following a low carbohydrate diet, most studies are small and uncontrolled11, 12. Only three small randomised controlled studies have been published comparing higher and lower carbohydrate diets, showing varying findings13–15.  One study found significant reductions in HbA1c and insulin use in the low carbohydrate diet group but no differences in cardiovascular risk markers or glycaemic variability15.  A second study reported more time spent in euglycaemia, less time in hypoglycaemia and less glucose variability on a low carbohydrate compared to high carbohydrate diet but no differences in mean glucose levels or cardiovascular risk markers. The researchers also noted impairments in cognitive function following the low carbohydrate diet14.  The third study found reduced glycaemic variability and time spent in hypoglycaemia on a low carbohydrate compared to high carbohydrate diet but no differences in time spent within the target range (3.9-10.0mmol/L) or cardiovascular risk markers13.

There are also a number of concerns cited around the use of low carbohydrate diets in those with T1D including the potential for micronutrient deficiencies, growth restriction in children, and the development of ketoacidosis, hypoglycaemia and dyslipidaemia11, 16, 17. One study found that a low carbohydrate diet may reduce the effectiveness of glucagon to correct hypoglycaemia18. Again, long-term adherence to a restricted diet and the impact on social normalcy also needs consideration11.

Current dietary recommendations for diabetes management

In their 2020 nutrition recommendations, the American Diabetes Association cite a lack evidence to be able to make specific recommendations about the ideal amount of carbohydrate for people with diabetes, including those with T1D, but highlight the importance of monitoring carbohydrate intake and considering the blood glucose response to dietary carbohydrate for improving postprandial glucose management19.  They also say that while there is some evidence for potential short-term (up to 1 year) benefits for the use of low carbohydrate diets for individuals with T2D and pre-diabetes, that long-term sustainability of such diets is an issue, and that this type of eating plan isn’t appropriate for certain groups including women who are pregnant or lactating, children, those with renal disease or disordered eating behavior, and people taking sodium-glucose cotransporter 2 inhibitors (SGLT2i).  They do, however, recommend limiting refined starches and added sugars and focusing on carbohydrates from vegetables, legumes, fruits, dairy foods and wholegrains. Similar recommendations are made in the Diabetes UK Evidence-based nutrition guidelines for the prevention and management of diabetes20.

Diabetes Australia released a position statement on low carbohydrate eating in 2018, which suggests that low carbohydrate diets may be useful in lowering blood glucose levels and weight in the short-term (up to 6 months) in people with T2D but that further research is needed to establish the effectiveness and safety of low carbohydrate diets for people with T1D21.  They also recommend that people with diabetes who wish to follow a low carb diet should do so in consultation with their diabetes healthcare team, including seeking advice from an Accredited Practising Dietitian experienced in diabetes management.

Diabetes UK published a position paper in 2017, with similar recommendations to Diabetes Australia 22. They conclude that low carbohydrate diets can be safe and effective in the short-term in managing weight, and improving glycaemic control and cardiovascular risk in people with T2D but that a low carbohydrate diet should not be regarded as a more superior or a better approach than other strategies.  They also highlight the lack of evidence for the use of low carbohydrate diets in people with T1D and caution against the use of these diets in children due to serious concerns about the impact on growth.

Dietary recommendations for diabetes – the bottom line

Based on research to date, there is insufficient evidence to support specific macronutrient recommendations for individuals with diabetes 23. Instead, diets varying in macronutrient distribution may be suitable to achieve nutritional goals23. It is recommended that macronutrient distribution is individualised, taking into account total energy needs and metabolic goals. Emphasis should be on healthy eating patterns containing nutrient-dense foods, with less focus on specific nutrients24, 25.  The eating plan also needs to align with an individual’s overall treatment plan including their medication regimen and physical activity levels25.  Nutrition recommendations should also take into consideration factors including cultural background, personal preferences, co-occurring conditions and socioeconomic factors19, 24.

A major benefit of low carbohydrate diets is the elimination of reduction in intake of processed starches and added sugars – foods that most people, diabetes or not, would benefit from removing from their diet.  Despite all the differences of opinion, most, if not all, health professionals would agree that there are many carbohydrate-containing foods that shouldn’t feature regularly in a healthy diet. This includes refined starches (such as biscuits, cakes, pastries, highly processed breakfast cereals and white bread) and added sugars (such as confectionary and sugar-sweetened drinks).   There is good evidence to support the health benefits of reducing intake of refined starches and added sugars, including for the prevention and management of T2D, and it is likely that most of the benefits of going low carb come from eliminating these foods, rather than restricting overall carbohydrate intake per se.

However, low carbohydrate diets also typically restrict foods (such as wholegrains, legumes, fruits and some vegetables) which are important sources of vitamins, minerals and dietary fibre and are the basis of eating patterns associated with a reduced risk of chronic disease and all-cause mortality.  Furthermore, there is evidence that low carbohydrate diets, particularly those high in animal foods, can worsen insulin sensitivity, increase T2D risk  and increase overall mortality26–28.   Diets high in saturated fat are similarly associated with increased insulin resistance and risk of T2D29–32.   And restricting carbohydrate intake and consuming more fat and protein, particularly from animal sources, has been shown to negatively impact the gut microbiome, potentially increasing inflammation and risk of gastrointestinal disease including colon cancer33–36. There is also increasing evidence for the role of the gut microbiome in the development of obesity and T2D37.

Low carbohydrate diets – role of the diabetes educator

Credentialled Diabetes Educators (CDEs) are able to provide general nutrition advice as part of the Diabetes Self-Management Education (DSME) process.  This includes general/introductory nutrition information on the role of food (including the role of carbohydrate foods) in diabetes management38.  However, if someone with diabetes is considering a low carbohydrate diet, it is important that they are referred to an Accredited Practising Dietitian (APD) for individualised medical nutrition therapy.

It is also important to advise people who are taking diabetes medications, particularly insulin, sulphonylureas and SGLT2i, of the need to seek medical advice prior to starting a low carbohydrate diet. Significantly reducing carbohydrate intake can increase the risk of hypoglycaemia for those taking insulin or sulphoylureas, and these medications will likely need adjustment.  Restricting carbohydrate while taking SGLT2i may lead to euglycaemic diabetic ketoacidosis (DKA) so these medications should be ceased prior to significantly reducing carbohydrate intake39, 40.   Regular blood glucose monitoring should be encouraged, to help with medication adjustment, along with monitoring of ketones in those at risk of DKA.

Conclusion

Low carbohydrate diets are one dietary approach that may help to improve blood glucose levels and weight management for those with T2D, at least in the short-term. However, they are not the only option, and may not be the best dietary approach for optimal long-term health.  If someone chooses to adopt a low carbohydrate eating plan, they should be encouraged to choose more plant sources of fat and protein over animal sources and to ensure a high intake of dietary fibre from plant foods including non-starchy vegetables, nuts, seeds and lower carbohydrate fruits. For those who are taking medication, particularly insulin, sulphonylureas and SGLT2i, close medical supervision is important to reduce the risk of hypoglycaemia and DKA.

Acknowledgements

I would like to acknowledge Dr Alan Barclay, APD, for reviewing and providing feedback on this article prior to publication.

References

1.

National Health and Medical Research Council (NHMRC). Nutrient Reference Values for Australia and New Zealand Including Recommended Dietary Intakes. Canberra; 2006. https://www.nhmrc.gov.au/about-us/publications/nutrient-reference-values-australia-and-new-zealand-including-recommended-dietary-intakes. Accessed January 28, 2020.

2.

Australian Bureau of Statistics. 4364.0.55.007 – Australian Health Survey: Nutrition First Results – Foods and Nutrients, 2011-12. https://www.abs.gov.au/ausstats/abs@.nsf/Lookup/by Subject/4364.0.55.007~2011-12~Main Features~Carbohydrate~705. Accessed February 3, 2020.

3.

Australian Bureau of Statistics. 4364.0.55.012 – Australian Health Survey: Consumption of Food Groups from the Australian Dietary Guidelines, 2011-12. https://www.abs.gov.au/ausstats/abs@.nsf/Lookup/by Subject/4364.0.55.012~2011-12~Main Features~Key Findings~1. Accessed February 4, 2020.

4.

Australian Bureau of Statistics. 4364.0.55.007 – Australian Health Survey: Nutrition First Results – Foods and Nutrients, 2011-12. https://www.abs.gov.au/ausstats/abs@.nsf/Lookup/by Subject/4364.0.55.007~2011-12~Main Features~Discretionary foods~700. Accessed February 3, 2020.

5.

Australian Bureau of Statistics. 4364.0.55.001 – National Health Survey: First Results, 2017-18. https://www.abs.gov.au/ausstats/abs@.nsf/Lookup/by Subject/4364.0.55.001~2017-18~Main Features~Fruit and vegetable consumption~105. Accessed February 4, 2020.

6.

Snorgaard O, Poulsen GM, Andersen HK, Astrup A. Systematic review and meta-analysis of dietary carbohydrate restriction in patients with type 2 diabetes. BMJ Open Diabetes Res Care. 2017;5(1). doi:10.1136/bmjdrc-2016-000354

7.

McArdle PD, Greenfield SM, Rilstone SK, Narendran P, Haque MS, Gill PS. Carbohydrate restriction for glycaemic control in Type 2 diabetes: a systematic review and meta-analysis. Diabet Med. 2019;36(3):335-348. doi:10.1111/dme.13862

8.

Sainsbury E, Kizirian N V., Partridge SR, Gill T, Colagiuri S, Gibson AA. Effect of dietary carbohydrate restriction on glycemic control in adults with diabetes: A systematic review and meta-analysis. Diabetes Res Clin Pract. 2018;139:239-252. doi:10.1016/j.diabres.2018.02.026

9.

Salas-Salvadó J, Becerra-Tomás N, Papandreou C, Bulló M. Dietary Patterns Emphasizing the Consumption of Plant Foods in the Management of Type 2 Diabetes: A Narrative Review. Adv Nutr. 2019;10:S320-S331. doi:10.1093/advances/nmy102

10.

Huo R, Du T, Xu Y, et al. Effects of Mediterranean-style diet on glycemic control, weight loss and cardiovascular risk factors among type 2 diabetes individuals: A meta-analysis. Eur J Clin Nutr. 2015;69(11):1200-1208. doi:10.1038/ejcn.2014.243

11.

Seckold R, Fisher E, de Bock M, King BR, Smart CE. The ups and downs of low-carbohydrate diets in the management of Type 1 diabetes: a review of clinical outcomes. Diabet Med. 2019;36(3):326-334. doi:10.1111/dme.13845

12.

Turton JL, Raab R, Rooney KB. Low-carbohydrate diets for type 1 diabetes mellitus: A systematic review. de Souza RJ, ed. PLoS One. 2018;13(3):e0194987. doi:10.1371/journal.pone.0194987

13.

Schmidt S, Christensen MB, Serifovski N, et al. Low versus high carbohydrate diet in type 1 diabetes: A 12-week randomized open-label crossover study. Diabetes, Obes Metab. 2019;21(7):1680-1688. doi:10.1111/dom.13725

14.

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, Obes Metab. 2017;19(10):1479-1484. doi:10.1111/dom.12953

15.

Krebs JD, Strong AP, 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. doi:10.6133/apjcn.2016.25.1.11

16.

de Bock M, Lobley K, Anderson D, et al. Endocrine and metabolic consequences due to restrictive carbohydrate diets in children with type 1 diabetes: An illustrative case series. Pediatr Diabetes. 2018;19(1):129-137. doi:10.1111/pedi.12527

17.

Bolla AM, Caretto A, Laurenzi A, Scavini M, Piemonti L. Low-carb and ketogenic diets in type 1 and type 2 diabetes. Nutrients. 2019;11(5). doi:10.3390/nu11050962

18.

Ranjan A, Schmidt S, Damm-Frydenberg C, et al. Low-carbohydrate diet impairs the effect of glucagon in the treatment of insulin-induced mild hypoglycemia: A randomized crossover study. Diabetes Care. 2017;40(1):132-135. doi:10.2337/dc16-1472

19.

Facilitating Behavior Change and Well-being to Improve Health Outcomes: Standards of Medical Care in Diabetes-2020. Diabetes Care. 2020;43:S48-S65. doi:10.2337/dc20-S005

20.

Dyson PA, Twenefour D, Breen C, et al. Diabetes UK evidence-based nutrition guidelines for the prevention and management of diabetes. Diabet Med. 2018;35(5):541-547. doi:10.1111/dme.13603

21.

Diabetes Australia. Low Carbohydrate Eating for People with Diabetes Position Statement.; 2018. https://www.diabetesaustralia.com.au/position-statements. Accessed February 4, 2020.

22.

Diabetes UK. Position Statement: Low-Carb Diets for People with Diabetes.; 2017. https://www.diabetes.org.uk/professionals/position-statements-reports/food-nutrition-lifestyle/low-carb-diets-for-people-with-diabetes. Accessed February 4, 2020.

23.

Wheeler ML, Dunbar SA, Jaacks LM, et al. Macronutrients, food groups, and eating patterns in the management of diabetes: A systematic review of the literature, 2010. Diabetes Care. 2012;35(2):434-445. doi:10.2337/dc11-2216

24.

Evert AB, Dennison M, Gardner CD, et al. Nutrition therapy for adults with diabetes or prediabetes: A consensus report. Diabetes Care. 2019;42(5):731-754. doi:10.2337/dci19-0014

25.

American Diabetes Association. 5. Lifestyle management: Standards of medical care in diabetes. Diabetes Care. 2019;42:S46-S60. doi:10.2337/dc19-S005

26.

de Koning L, Fung TT, Liao X, et al. Low-carbohydrate diet scores and risk of type 2 diabetes in men. Am J Clin Nutr. 2011;93(4):844-850. doi:10.3945/ajcn.110.004333

27.

Noto H, Goto A, Tsujimoto T, Noda M. Low-carbohydrate diets and all-cause mortality: a systematic review and meta-analysis of observational studies. PLoS One. 2013;8(1):e55030. doi:10.1371/journal.pone.0055030

28.

Adeva-Andany MM, González-Lucán M, Fernández-Fernández C, Carneiro-Freire N, Seco-Filgueira M, Pedre-Piñeiro AM. Effect of diet composition on insulin sensitivity in humans. Clin Nutr ESPEN. 2019;33:29-38. doi:10.1016/j.clnesp.2019.05.014

29.

Riserus U. Fatty acids and insulin sensitivity. Curr Opin Clin Nutr Metab Care. 2008;11(2):100-5. doi: 10.1097/MCO.0b013e3282f52708.

30.

Riserus U, Willett WC, Hu FB. Dietary fats and prevention of type 2 diabetes. Prog Lipid Res. 2009;48(1):44-51. Epub 2008 Nov 7.

31.

Rivellese AA, Lilli S. Quality of dietary fatty acids, insulin sensitivity and type 2 diabetes. Biomed Pharmacother. 2003;57(2):84-87. doi:10.1016/S0753-3322(03)00003-9

32.

Haag M, Dippenaar NG. Dietary fats, fatty acids and insulin resistance: short review of a multifaceted connection. Med Sci Monit. 2005;11(12):RA359-67. Epub 2005 Nov 24.

33.

Brinkworth GD, Noakes M, Clifton PM, Bird AR. Comparative effects of very low-carbohydrate, high-fat and high-carbohydrate, low-fat weight-loss diets on bowel habit and faecal short-chain fatty acids and bacterial populations. Br J Nutr. 2009;101(10):1493-1502. doi:10.1017/S0007114508094658

34.

Russell WR, Gratz SW, Duncan SH, et al. High-protein, reduced-carbohydrate weight-loss diets promote metabolite profiles likely to be detrimental to colonic health. Am J Clin Nutr. 2011;93(5):1062-1072. doi:10.3945/ajcn.110.002188

35.

Agans R, Gordon A, Kramer DL, Perez-Burillo S, Rufián-Henares JA, Paliy O. Dietary fatty acids sustain the growth of the human gut microbiota. Appl Environ Microbiol. 2018;84(21). doi:10.1128/AEM.01525-18

36.

David LA, Maurice CF, Carmody RN, et al. Diet rapidly and reproducibly alters the human gut microbiome. Nature. 2014;505(7484):559-563. doi:10.1038/nature12820

37.

David LA, Maurice CF, Carmody RN, et al. Diet rapidly and reproducibly alters the human gut microbiome. Nature. 2014;505(7484):559-563. doi:10.1038/nature12820

38.

Dietitians Association of Australia (DAA) and the Australian Diabetes Educators Association (ADEA). The Role of Credentialled Diabetes Educators and Accredited Practising Dietitians in the Delivery of Diabetes Self Managment and Nutrition Services for People with Diabetes.; 2015. https://www.adea.com.au/About_Us/Policy.

39.

Hayami T, Kato Y, Kamiya H, et al. Case of ketoacidosis by a sodium-glucose cotransporter 2 inhibitor in a diabetic patient with a low-carbohydrate diet. J Diabetes Investig. 2015;6(5):587-590. doi:10.1111/jdi.12330

40.

Yabe D, Iwasaki M, Kuwata H, et al. Sodium-glucose co-transporter-2 inhibitor use and dietary carbohydrate intake in Japanese individuals with type 2 diabetes: A randomized, open-label, 3-arm parallel comparative, exploratory study. Diabetes, Obes Metab. 2017;19(5):739-743. doi:10.1111/dom.12848

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