Although current treatments for diabetic retinopathy (DR) can improve vision and delay the progression of DR, they do not affect the progression of diabetes—which requires changes in diet and lifestyle.1,2 This article outlines the research supporting the benefits of a plant-based diet for patients with type 2 diabetes and a single-center case series investigating the effect of a 2-minute nutritional intervention in the retina practice.

AT A GLANCE

  • Plant-based diets are associated with reduced cardiovascular disease, hypertension, and diabetes.
  • The authors designed a study to evaluate whether a brief discussion of plant-based nutrition with patients with type 2 diabetes could motivate them to change their diet and improve their glycemic control.
  • The study found that, of 283 consecutive patients with type 2 diabetes, 21% incorporated a more plant-based diet, 80% of whom had improved glycemic control, which has been shown to prevent or delay diabetic retinopathy.

THE EVIDENCE

A recent study of the global burden of type 2 diabetes estimated that 70% (14 million) of new cases can be attributed to dietary factors, such as the intake of insufficient whole grains, excessive refined rice and wheat, and excess processed meat.2

Large observational cohort studies indicate that a plant-based diet is associated with reduced mortality, cardiovascular disease, diabetes, and hypertension.3-5 One prospective cohort study in Taiwan reported that vegetarians and non-vegetarians who converted to a vegetarian diet had a 35% and 53% reduction in the risk of diabetes, respectively, compared with non-vegetarians.6

Interventional trials also demonstrate the benefits of plant-based dietary patterns. One randomized controlled study showed that a low-fat vegan diet improved glycemic control in patients with type 2 diabetes more effectively than the standard American Diabetes Association diet at that time.7 A 2014 meta-analysis and systematic review established that a vegetarian diet is associated with a significant reduction in hemoglobin A1c and improved glycemic control for individuals with type 2 diabetes.8 More recently, two intervention studies demonstrated that plant-based diets and exercise were more effective at improving glycemic control and sometimes reversing the effects of type 2 diabetes compared with typical diabetes care.9,10

Evidence from these and other studies demonstrates the benefits of a plant-based diet in improving glycemic control and reducing mortality and microvascular and macrovascular complications of diabetes.11

Results from the Action to Control Cardiovascular Risk in Diabetes (ACCORD) study and the UK Prospective Diabetes Study (UKPDS), both of which studied patients with type 2 diabetes, showed that good glycemic control reduces the incidence and risk of progression of DR.12 In the ACCORD study, strict glycemic control resulted in a 1/3 reduction in the risk of DR progression. In the ACCORD follow-on study (ACCORDION), even when hemoglobin A1c levels became equivalent once the initial study had been completed, the risk of DR progression over the subsequent 4 years was reduced from 12.7% in the standard treatment group to 5.8% in the intensive treatment group.12

We designed a study within our practice to determine if a brief plant-based nutritional intervention in a retina practice could motivate patients with diabetes to meaningfully improve their glycemic control, thereby improving their health and reducing the risk of long-term complications.

STUDY DESIGN AND METHODS

We conducted a consecutive case series of prospectively collected established patients with type 2 diabetes from a single retina practice. The inclusion criteria were patients treated with medication for their diabetes, with no dementia, and who lived at home so they could implement dietary changes. The study continued for 6 months.

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<p>Figure 1. This nutrition card can help clinicians highlight to patients the key foods to eat or avoid in their daily diets. Images courtesy of Allison Menezes, MD.</p>

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Figure 1. This nutrition card can help clinicians highlight to patients the key foods to eat or avoid in their daily diets. Images courtesy of Allison Menezes, MD.

NUTRITION CARD

CLICK HERE to visit www.moreplantsmd.com/nutr-card to download this nutrition card.

All patients with diabetes had previously received a 2-minute discussion on the benefits of whole food plant-based nutrition and an 8x11 informational card describing foods to eat, foods to avoid, and where to access evidence-based nutrition information (Figure 1). Patients were encouraged to eat primarily vegetables, fruits, beans, and whole grains 5 days a week, with flexibility for some animal products on weekends. Patients were also informed that the implementation of these recommendations could improve glucose levels within 16 days.13 As such, it was important for them to check glucose levels regularly and notify their primary care physician if levels decreased so that medications could be adjusted.

During follow-up visits, patients were surveyed as to whether they had changed their diet and whether their glycemic control or weight had changed. Age, duration of diabetes, and level of DR were documented. For patients who indicated that they adopted a more plant-based diet, they self-reported the duration and percent of plants in their diet and any change in hemoglobin A1c levels, fasting glucose levels, medications, and weight.

Days of plant-based eating included consuming vegetables, fruits, legumes, and whole grains with minimal red meat, chicken, fish, eggs, or dairy products. Whole foods rather than processed foods were emphasized. Patients who reported improved hemoglobin A1c, reduced diabetes medications, or improved fasting glucose measurements (without additional medications) were designated to have improved glycemic control.

Results

Over 6 months, 283 consecutive established patients with type 2 diabetes were identified. Of these, 60 patients (21%) changed their diets to include more plants (with at least 2 days per week designated as plant based). The average age and duration of diabetes in patients who chose their usual diet or who adopted a more plant-based diet were similar. Of the 60 patients who chose a more plant-based diet, 24 (40%) had nonproliferative DR, 11 (18%) had proliferative DR, and 26 (43%) had diabetic macular edema (DME). There was no significant change in retinopathy noted in the short duration of this study other than less DME with anti-VEGF therapy.

Of the 60 patients who changed to a more plant-based diet (range: 15% to 100% plant-based), 80% improved their hemoglobin A1c by an average of 1.0 percentage points (range: 0 to 4.0; Figure 2). Weight loss was reported in 68% of these patients with an average loss of 11 lbs (range: 0 to 98 lbs; Figure 3). As expected, patients who ate a plant-based diet more than 50% of the week had better results, with an average improved hemoglobin A1c of 1.3 percentage points and weight loss of 14.3 lbs.

One patient with type 2 diabetes for 15 years was on 175 units of insulin and had DME. He adopted a 100% whole food plant-based diet, and within 3 months, his hemoglobin A1c decreased from 9 to 5.2 percentage points. Within a year, he had lost 98 lbs and discontinued all medications for diabetes and hypertension. He required intermittent intravitreal anti-VEGF injections for a year and none thereafter.

<p>Figure 2. Study results of 60 patients with diabetes who focused on a plant-based diet suggest that patients who had a plant-based diet more than 50% of the time experienced a higher reduction in hemoglobin A1c percentage points compared with patients who had a plant-based diet less than 50% of the time.</p>

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Figure 2. Study results of 60 patients with diabetes who focused on a plant-based diet suggest that patients who had a plant-based diet more than 50% of the time experienced a higher reduction in hemoglobin A1c percentage points compared with patients who had a plant-based diet less than 50% of the time.

<p>Figure 3. Study results of 60 patients with type 2 diabetes who focused on a plant-based diet showed that those who stayed with a plant-based diet more than 50% of the time experienced more weight loss than patients who had a plant-based diet less than 50% of the time.</p>

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Figure 3. Study results of 60 patients with type 2 diabetes who focused on a plant-based diet showed that those who stayed with a plant-based diet more than 50% of the time experienced more weight loss than patients who had a plant-based diet less than 50% of the time.

Limitations and Future Recommendations

The limitations of our study are evidenced by self-reported findings and the results from a single health care provider. Future studies should use a larger sample size, blinded interviewers, objective glucose and weight measurements, and multiple providers. If these findings are reproducible, then this brief, consistent nutritional intervention could be applicable across multiple medical specialties to scale the message of the benefits of plant-based eating for our patients' health and the reduction of risk and progression of DR.

KEY TAKEAWAYS 

After receiving brief nutritional information, 21% of patients in our study were motivated to adopt a more plant-based diet. This resulted in improved glycemic control in 80% of patients and weight loss in 68% of these patients, suggesting that retina specialists have an opportunity to positively affect the long-term health of patients and, ultimately, reduce the complications of diabetes with a simple, brief intervention.

1. Kherani S, Kim JE. A DRCR Retina Network Update A to Z. Retina Today. 2022;16(6):42-44.

2. O'Hearn M, Lara-Castor L, Cudhea F, et al. Incident type 2 diabetes attributable to suboptimal diet in 184 countries. Nature Medicine. 2023;29:982-995.

3. Shan Z, Li Y, Baden MY, et al. Association between healthy eating patterns and risk of cardiovascular disease. JAMA Intern Med. 2020;180(8):1090-1100. 

4. Hu Y, Liu G, Yu E, et al. Low-carbohydrate diet scores and mortality among adults with incident type 2 diabetes. Diabetes Care. 2023;46(4):874-884.

5. Appel LJ, Moore TJ, Obarzanek E, et al. A clinical trial of the effects of dietary patterns on blood pressure. N Engl J Med. 1997;336(16):1117-1124.

6. Chiu THT, Pan WH, Lin MN, Lin CL. Vegetarian diet, change in dietary patterns, and diabetes risk: a prospective study. Nutr Diabetes. 2018;8(1):12.

7. Barnard ND, Cohen J, Jenkins DJA, et al. A low-fat vegan diet improves glycemic control and cardiovascular risk factors in a randomized clinical trial in individuals with type 2 diabetes. Diabetes Care. 2006;29(8):1777-1783.

8. Yokoyama Y, Barnard ND, Levin SM, Watanabe M. Vegetarian diets and glycemic control in diabetes: a systematic review and meta-analysis. Cardiovasc Diagn Ther. 2014;4(5):373-382.

9. Hanick C, Peterson CM, Sabate J, Davis BC. Effects of a plant-based intensive lifestyle intervention in adults with type 2 diabetes: a randomized controlled trial. Diabetes. 2022;71(Supp 1):551-P.

10. Tripathi P, Kadam N, Sharma B, et al. Effectiveness of an intensive lifestyle modification program on type 2 diabetes remission in Indian population. Diabetes. 2023;72(Supp 1):1790-P.

11. McMacken M, Shah S. A plant-based diet for the prevention and treatment of type 2 diabetes. J Geriatr Cardiol. 2017;14(5):342-354.

12. Ferris III FL, Nathan DM. Preventing diabetic retinopathy progression. Ophthalmology. 2016;123(9):1840-1842.

13. Anderson JW, Ward K. High-carbohydrate, high-fiber diets for insulin-treated men with diabetes mellitus. Am J Clin Nutr. 1979;32(11):2312-2321.