Low-Carb Diets:Their Role in Blindness Prevention

There is much to be said about the role of diet in minimising the risks associated with type 1 and type 2 diabetes. As primary practitioners we have a responsibility to share evidence based information and tools with
our patients. In doing so, we can contribute significantly to their longevity and quality of life.

Recently I experienced one of those moments that cuts you to the core as a practitioner. A 32-year-old female patient came into my practice for an emergency appointment complaining of watery vision in her left eye. Without the privilege of pretests, this was a case of playing detective. I quickly established that Karen* was type 1 diabetic on an insulin pump, though if I hadn’t been offered this piece of knowledge, I’d have assumed the person in front of me was a healthy individual with their life ahead of them – such was her presentation. Karen proceeded to tell me that she had had three surgeries on her eyes, the details of which she was unsure. In terms of her insulin, she was running 40Iµ basal and about 10Iµ in response to meals, so in the vicinity of 70-80Iµ per day – not extreme but a reasonable insulin load. Despite this, she was running a glucose level of 8mmol/L which would approximate to an HbA1c of 59mmol/mol (again not extreme in terms of modern aims, in fact close to the 58mmol/mol often recommended). I quickly learnt that Karen was taking vitamin D and folic acid, and she was under the care of a fertility specialist, as she was having difficulty starting a family. I tested Karen’s vision and found that she had hand movement vision in her left eye and her right eye was best corrected to 6/9. Dilation drops were administered and at that moment, I experienced something no eye care practitioner would ever hope to see, especially in a young patient with so much ahead of her. My heart began to break. I don’t know whether it was the fact that we were of similar age, or that I am lucky enough to have a young daughter of my own. Or perhaps it was the memory of a colleague ophthalmologist in Ballina the year prior who showed me a photo of a 20-year-old patient and said, “this girl will not see her children grow up”. My thoughts focussed on Karen’s prospective pregnancy. If her eyes, and potentially her other organs, looked as bad as they did now, how would the pregnancy demands of growth factors, hormones, blood pressure and insulin resistance affect her? And, had she been given the best information earlier, could all of this been prevented?


As optometrists we are very aware of the graph from Skyler,1 which shows the relationship between HbA1c and the risk of microvascular complications. The graph clearly demonstrates that a patient’s risk of complications increases with an A1c higher than 53 mmol/mol, with the retina being most susceptible to damage. While a very low carb diet was traditionally recommended to manage type 1 diabetes2,3 concerns surrounding hypoglycaemia, ketoacidosis, dyslipidemia, nutrient deficiency, growth failure in children and sustainability became barriers to implementation. The discovery of insulin as a novel management tool for type 1 diabetes in 1921 was seen as groundbreaking and recognised with a Nobel Prize in 1923.4 Over the years, the quality of insulin became more pure, more consistent in its potency and longer lasting. However, more recently, very low carbohydrate diets have regained favour. In May 2018, Lennerz, Barton, Bernstein et al.5 observed that a very low carbohydrate, moderate protein diet, as described by Dr Bernstein’s book “Doctor Bernstein’s Diabetes Solution”, gave a cohort of type 1 diabetes patients (the Type 1 Grit cohort) an average HbA1c close to 38mmol/ mol. The cohort was able to achieve these fantastic levels of glucose control with low rates of adverse events. While this data gives cause for hope, especially when examining some of the cohort’s anecdotes, the authors are quick to state that at this point it is merely observational and suffers from self-selection bias. Further study to determine the long term safety of the diet, along with high quality randomised controlled trials are required. This view was reiterated in a letter to the editor later the same year titled, Management of Type 1 Diabetes With a Very Low–Carbohydrate Diet: A Word of Caution. 6 Despite these reservations, the study prompted the American Diabetes Association to shift its position with regards to low and very low carbohydrate diets for diabetes management. In its April 2019 Consensus Report,7 with regards to type 1 diabetes, the Association stated that a meta-analysis of random control trials comparing diets with >45% carbohydrates to <45% carbohydrates showed a more pronounced benefit to A1c when a patient’s diet is restricted to below 26% carbohydrates in the first six months, but not into 12 and 24 months. They also stated that a meta-analysis comparing low carbohydrate diets (<40%) against low fat diets (<30%) found that the former was more effective in improving A1c, lowering triglycerides and blood pressure, increasing high-density lipoprotein cholesterol, and reducing diabetic medications in trials up to six months. Thirdly, a meta-analysis of studies of low carbohydrate eating patterns out to one year also found that the larger the carbohydrate restriction, the better the A1c. While current evidence shows that eating this way, with its often greater consumption of saturated fats, does not appear to increase the risk of cardiovascular disease, longer term data is needed, in particular into the potential cardiovascular risks often associated with low-density lipoproteins.8-10


With all of this knowledge in mind, you may be asking why I was so heartbroken when I examined Karen? After all, if I were to encourage her to adapt a very low carbohydrate diet, she may be able to achieve an insulin dose closer to 40Iµ per day, as per the Type 1 Grit cohort. Additionally, she may be able to achieve an A1c closer to 38mmol/mol (as opposed to = 58mmol/mol) which would extend the life of her retina vessels. In doing so, she may not need to rely on an insulin pump and, with less insulin she may find it easier to start a family… In turn, she will be gifted with the opportunity to see her family grow up, both figuratively and literally.


COVID-19 has provided evidence of the increased health risks people face when they live with co-morbidities, especially in the realms of metabolic dysfunction and diabetes. Our 2020 Australian of the Year, ophthalmologist, Dr James Muecke has provided evidence of the impact that poor diet has on our health. As a strategy to stem the rising tide of type 2 diabetes, he has called for greater control over the amount of sugar and carbohydrates prescribed in our diet. Shouldn’t we, as primary practitioners, also make it our responsibility to step up and do our best to stem the rising tide? By sharing information and tools with those at risk of diabetes we can help optimise their survival rate and their quality of life – after all, everyone deserves the opportunity to watch their families grow up around them.

I am an optometrist with Visique Shattky in Hawke’s Bay, New Zealand.

I have special interests in behavioural optometry, sports vision, TBI recovery, dry eye and specialty lens fitting.

*Patient name changed for anonymity.

References: 1. Skyler JS. Endocrinol Metab Clin North Am. 1996; 25:243-254

2. 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. Paediatr Diabetes. 2018; 19 (1):129-137

3. Kanikarla-Marie P, Jain SK. Hyperketonemia and ketosis increase the risk of complications in type 1 diabetes. Free Radic Biol Med. 2016;95:268-277

4. Newburgh LH, Marsh PL. The use of a high fat diet in treatment of diabetes mellitus. Arch Intern Med (chic). 1921;27 (6):699-705

5. Lennerz BS, Barton A, Bernstine RK, et al. Management of Type 1 Diabetes With a Very Low-Carbohydrate Diet. Paediatrics. 2018;141(6):e20173349

6. Management of Type 1 Diabetes With a Very Low– Carbohydrate Diet: A Word of Caution. Elizabeth J. MayerDavis, Lori M. Laffel and John B. Buse Pediatrics 2018, 142 (2) e20181536B

7. Evert AB, Dennison M, Gardner CD, et al. Nutrition Therapy for Adults With Diabetes or Prediabets: A Consensus Report. Diabetes Care. 2019 May; 42(5): 731-754.

8. Bhanpuri NH, Hallberg SJ, Williams PT et a;. Cardiovascular disease risk factor responses to a type 2 diabetes care model including nutritional ketosis induced by sustained carbohydrate restriction at 1 year: an open label, non-randomised, controlled study. Cardivasc Diabetol. 2018;17:56

9. Forsythe CE, Phinny SD, Fernandez ML et al. Comparison of low fat and low carbohydrate diets on circulating fatty acid composition and markers of inflammation. Lipids 2008;43:65-77

10. Tay J, Luscombe-Marsh ND, Thompson CH, et al. Comparison of low- and high-carbohydrate diets for type 2 diabetes management: a randomised trial. Am J Clin Nutr 2015;102:780-790


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