A Plant-Based Diet for the Prevention and Treatment of Diabetes

The global prevalence of diabetes in 2019 was 9.3% (463 million people). (1) In the US alone, it is estimated that in 2060 that 2 in 5 people will be diagnosed with diabetes; a shockingly high statistic. (2) In 2017, $327 billion was spent on direct and indirect costs associated with diabetes in the US alone, which was a 26% increase from 2012. (3) Aside from the monetary expenditure, diabetes causes tremendous suffering and a lowered quality of life and is primarily a preventable disease of lifestyle. For the purpose of this article, when I mention diabetes, I am referring to type 2 diabetes.

Insulin resistance pathogenesis

As a person gains weight (usually from caloric excess), their adipocytes (fat cells) grow in number and size, and they eventually start to accumulate fat in tissue and organs, where it isn’t supposed to be, such as muscle and liver. This intracellular lipid accumulation in muscle and liver cells impairs insulin signalling within the cell. Usually when insulin binds to receptors on a cell, it causes a cascade of intracellular reactions to place ports into the cell membrane to allow glucose to enter the cell. When there is fat sitting within the cell, it impairs these reactions and fewer ports are placed in the cell membrane, resulting in less glucose entering the cells and more staying in our blood stream, causing high blood glucose levels. (4)

Furthermore, long term exposure of the beta cells in the pancreas (the insulin-producing cells) to fatty acids prevents adequate insulin secretion in response to high blood glucose levels. Beta cells take up the circulating fatty acids and store them as triacylglycerol. When in excess, this intracellular lipid inhibits the beta cells from producing sufficient insulin and causes apoptosis (cell death) of the beta cells, resulting in the loss of both the total number and functional number of beta cells. (5)

There are other contributing factors to insulin resistance in the pathogenesis of diabetes, such as dysbiosis and reduced short-chain fatty acid production, inflammatory mediation, leptin resistance, etc, but our focus is going to be on the main pathways detailed above. (6)

The treatment for diabetes

Current treatment modalities for type 2 diabetes focus on either increasing insulin production by the beta cells in the pancreas, increasing insulin sensitivity in the cells, or ultimately, replacing insulin with injected insulin when the other treatments fail, or the diabetes is severe enough. While these medications are vital to keep a person alive and prevent further complications of persistently elevated blood glucose, they are not addressing the underlying disease process of insulin resistance. Therefore, even if blood glucose levels are adequately controlled on medication initially, the insulin resistance will continue to worsen, and the medication requirements will continue to rise if we don’t simultaneously address the insulin resistance.

What is meant by “reversing diabetes”?

The American College of Lifestyle Medicine defines reversal of type 2 diabetes as the “normalisaiton of blood glucose and HbA1c (a marker of glucose control over the previous 3 months), and the discontinuation of ALL diabetes medication (oral and injectable).” The remission of type 2 diabetes is defined as “HbA1c of <5.7 (non-diabetic normal range) for at least 1 year with no active pharmacology or procedures”. (7)

Plant-based diets for diabetes prevention

Several large cohort studies have shown that adherence to a plant-based diet is preventive against type 2 diabetes. The Adventist Health Study 2 (8) that looked at nearly 61,000 people, found that the incidence of diabetes reduced in a stepwise fashion as individuals removed animal products from their diet, with a vegan diet being the most protective (2.9% incidence as compared to 7.6% incidence in non-vegetarians). BMI can be a confounder, as an elevated BMI independently increases the risk of diabetes, however, even after controlling for BMI, the vegans still had a significantly lower risk. A 17 year follow up of the Adventist Mortality and Adventist Health Study (9) showed that weekly meat consumption was associated with a 74% increased risk of developing diabetes compared to a vegetarian diet, again with persistent lower risk in the vegetarians after controlling for BMI.

A cohort of over 4,000 Taiwanese individuals found that vegetarian men had half the risk, and vegetarian post-menopausal woman had a quarter of the risk of developing diabetes compared to non-vegetarians. (10)

And the largest prospective study of plant-based diets, looked at the incidence of diabetes in the Nurses Health Study, the Nurses Health Study 2 and the Health Professionals Follow Up study, amounting to over 4.1 million person-years of follow up. (11) It showed that adherence to a healthful plant-based eating pattern was associated with a 34% lower risk of developing diabetes, compared to those eating more animal products and processed foods.

Similar results were reported from the European Prospective Investigation into Cancer and Nutrition (EPIC) study. (12) Over 340,000 individuals were followed for 11.7 years, and the results showed that processed meat, red meat, total meat and poultry intakes were associated with an increased risk of diabetes.

And finally, the Rotterdam study showed that a higher intake of plant-based foods and a lower intake of animal products was associated with a lower risk of prediabetes and type 2 diabetes. (13)

Plant-based diets for diabetes treatment

Conventional knowledge and many recommendations made to patients by doctors and dietitians, leave patients in fear of consuming carbohydrates thinking that they will increase blood glucose and result in poorer control of their diabetes. As we can see from the pathophysiology of diabetes, the problem is not glucose, the problem is the inability of the body to handle glucose due to intracellular lipid accumulation.

It is not new knowledge that plant-based diets can improve diabetic control. In 1979, 20 insulin-dependent men with diabetes were placed on a predominantly plant-based diet for 16 days in a metabolic ward study (they stayed in a ward and everything they ate was controlled). Despite maintaining their weight, 9 of the 20 were able to eliminate their insulin entirely and had improved glycaemic control despite having discontinued their insulin, and the remaining 11 had significantly reduced insulin requirements. (14)

A 74-week randomised control trial of 99 participants compared a low fat vegan diet to a diet following the American Diabetes Association guidelines for people with diabetes, and the vegan group had significantly greater reductions in HbA1c, total and LDL cholesterol. (15)

Similarly, 93 participants were randomised to consume a vegan diet including fish, or a diet recommended by the Korean Diabetes Association, and the results showed that the vegan plus fish diet had more significant reductions in HbA1c compared to the control diet, even after controlling for energy intake and waist circumference. They also found that the more adherent participants were, the more marked the results. (16)

Two systematic reviews and meta-analyses in 2014 and 2018 looking at controlled trials found that vegetarian and vegan diets were associated with improved glycaemic control and HbA1c in individuals with diabetes. This effect was greater that improvements in comparator diets. (17, 18)

The improvement in diabetic control can largely be attributed to the weight loss experienced on a vegan diet, due to the low caloric density of the diet. However, evidence also suggests that increases in fiber and vegetable protein intake, reduction in saturated fat and animal protein intake, and reduced intramyocellular lipid play a role too. (19)

There is also evidence that a plant-based diet can assist in treating the complications of diabetes. Diabetes can become complicated by chronic kidney disease, and when the glomeruli are damaged, they leak protein into the urine, which is what doctors commonly measure as one of the markers of kidney disease. Substituting meat for plant-based sources of protein, such as soy, can reduce proteinuria in patients with chronic kidney disease (20) as well as mortality resulting from CKD (21). Small randomised controlled trials have also shown that plant-based diets can alleviate the burning sensation associated with diabetic neuropathy (nerve damage, commonly causing burning and painful sensations in the feet). (22, 23)

What about fruit intake and diabetes?

A common misperception is that because fruit contains various sugars, it should not be consumed by people with diabetes. However, the sugar found in fruit is not the same as the fruit found in cookies. Fruit in sugar comes packaged together with fiber (which firstly reduces the rate of absorption of the glucose, reducing spikes in blood glucose compared to the sugar found in processed foods, and secondly, results in increased production of short chain fatty acids in the gut, that have been shown to improve glycaemic control), phytonutrients, antioxidants, and anti-inflammatory compounds.

Higher fruit intake has been shown by several studies to reduce the incidence of diabetes. Looking At the Nurses Health Study, the Nurses Health Study 2 and the Health Professionals Follow Up Study, increased consumption of whole fruits was associated with lower rates of diabetes, despite varying glycaemic load values, whereas fruit juice was associated with increased rates of diabetes. (24)

Another study done on over 7,500 Australians, followed up for over 10 years, found that total fruit intake was associated with improved beta cell function, improved insulin sensitivity, and reduced rates of diabetes, after adjusting for other diet and lifestyle factors. (25) Similarly, almost 7,000 individuals participated in the Stockholm Diabetes Prevention Program cohort, and those with the highest total fruit and vegetable intake had a 24% reduced risk of developing both diabetes and prediabetes. (26)

Studies have shown that there have been no adverse effects reported of supplementing a diet with additional fruit, and it may actually provide beneficial effects on blood glucose and HbA1c levels. As such, fruit intake should not be restricted in individuals with diabetes. (27, 28, 29, 30).

Conclusion

Plant-based diets have been shown to reduce the risk of developing diabetes and can be used to improve glycaemic control in those with diabetes, as well as to reduce diabetic medication burden. There is no evidence that whole foods carbohydrate sources, including fruit, have a negative impact on glycaemic control, and their consumption should be encouraged as part of a healthful diet, even in those living with diabetes.

References

1. Saeedi P, Petersohn I, Salpea P, Malanda B, Karuranga S, Unwin N, Colagiuri S, Guariguata L, Motala AA, Ogurtsova K, Shaw JE, Bright D, Williams R; IDF Diabetes Atlas Committee. Global and regional diabetes prevalence estimates for 2019 and projections for 2030 and 2045: Results from the International Diabetes Federation Diabetes Atlas, 9th edition. Diabetes Res Clin Pract. 2019 Nov;157:107843.

2. Lin, J., Thompson, T.J., Cheng, Y.J. et al. Projection of the future diabetes burden in the United States through 2060. Popul Health Metrics 16, 9 (2018).

3. American Diabetes Association; Economic Costs of Diabetes in the U.S. in 2017. Diabetes Care 1 May 2018; 41 (5): 917–928.

4. Mahadev K, Zilbering A, Zhu L, Goldstein BJ. Insulin-stimulated hydrogen peroxide reversibly inhibits protein-tyrosine phosphatase 1b in vivo and enhances the early insulin action cascade. J Biol Chem. 2001 Jun 15;276(24):21938-42.

5. Oh YS, Bae GD, Baek DJ, Park EY, Jun HS. Fatty Acid-Induced Lipotoxicity in Pancreatic Beta-Cells During Development of Type 2 Diabetes. Front Endocrinol (Lausanne). 2018;9:384.

6. Pancreas: Roy Taylor; Type 2 Diabetes: Etiology and reversibility. Diabetes Care 1 April 2013; 36 (4): 1047–1055.

7. Buse JB, Caprio S, Cefalu WT, et al. How do we define cure of diabetes? Diabetes Care. 2009;32(11):2133-2135.

8. Tonstad S, Butler T, Yan R, et al. Type of vegetarian diet, body weight, and prevalence of type 2 diabetes. Diabetes Care 2009; 32: 791–796.

9. Vang A, Singh PN, Lee JW, et al. Meats, processed meats, obesity, weight gain and occurrence of diabetes among adults: findings from Adventist Health Studies. Ann Nutr Metab 2008; 52: 96–104.

10. Chiu TH, Huang HY, Chiu YF, et al. Taiwanese vegetarians and omnivores: dietary composition, prevalence of diabetes and IFG. PLoS One 2014; 9: e88547.

11. Satija A, Bhupathiraju SN, Rimm EB, et al. Plant-based dietary patterns and incidence of type 2 diabetes in US men and women: results from three prospective cohort studies. PLoS Med 2016; 13: e1002039.

12. Consortium IA, Bendinelli B, Palli D, Masala G, Sharp SJ, Schulze MB, Guevara M, van der ADL, Sera F, Amiano Pet al.. Association between dietary meat consumption and incident type 2 diabetes: the EPIC-InterAct study. Diabetologia. 2013;56:47–59.

13. Chen Z, Zuurmond MG, van der Schaft N, Nano J, Wijnhoven HAH, Ikram MA, Franco OH, Voortman T. Plant versus animal based diets and insulin resistance, prediabetes and type 2 diabetes: the Rotterdam Study. Eur J Epidemiol. 2018;33:883–93.

14. Anderson JW, Ward K. High-carbohydrate, high-fiber diets for insulin-treated men with diabetes mellitus. Am J Clin Nutr. 1979 Nov;32(11):2312-21.

15. Barnard ND, Cohen J, Jenkins DJ, Turner-McGrievy G, Gloede L, Green A, Ferdowsian H. A low-fat vegan diet and a conventional diabetes diet in the treatment of type 2 diabetes: a randomized, controlled, 74-wk clinical trial. Am J Clin Nutr. 2009 May;89(5):1588S-1596S.

16. Lee YM, Kim SA, Lee IK, Kim JG, Park KG, Jeong JY, Jeon JH, Shin JY, Lee DH. Effect of a Brown Rice Based Vegan Diet and Conventional Diabetic Diet on Glycemic Control of Patients with Type 2 Diabetes: A 12-Week Randomized Clinical Trial. PLoS One. 2016 Jun;11(6):e0155918.

17. 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 Oct;4(5):373-82.

18. Toumpanakis A, Turnbull T, Alba-Barba IEffectiveness of plant-based diets in promoting well-being in the management of type 2 diabetes: a systematic reviewBMJ Open Diabetes Research and Care 2018;6:e000534.

19. Barnard ND, Katcher HI, Jenkins DJ, Cohen J, Turner-McGrievy G. Vegetarian and vegan diets in type 2 diabetes management. Nutr Rev. 2009 May;67(5):255-63.

20. Azadbakht L, Atabak S, Esmaillzadeh A. Soy protein intake, cardiorenal indices, and C-reactive protein in type 2 diabetes with nephropathy: a longitudinal randomized clinical trial. Diabetes Care 2008; 31: 648–654.

21. Almeida JC, Zelmanovitz T, Vaz JS, et al. Sources of protein and polyunsaturated fatty acids of the diet and microalbuminuria in type 2 diabetes mellitus. J Am Coll Nutr 2008; 27: 528–537.

22. Crane MG, Sample C. Regression of diabetic neuropathy with total vegetarian (Vegan) diet. J Nutr Med 1994; 4: 431–439.

23. Bunner AE, Wells CL, Gonzales J, et al. A dietary intervention for chronic diabetic neuropathy pain: a randomized controlled pilot study. Nutr Diabetes 2015; 5: e158.

24. Muraki I, Imamura F, Manson JE, Hu FB, Willett WC, van Dam RM, Sun Q. Fruit consumption and risk of type 2 diabetes: results from three prospective longitudinal cohort studies. BMJ. 2013 Aug 28;347:f5001.

25. Bondonno NP, Davey RJ, Murray K, et al. Associations Between Fruit Intake and Risk of Diabetes in the AusDiab Cohort. J Clin Endocrinol Metab. 2021;106(10):e4097-e4108.

26. Barouti AA, Tynelius P, Lager A, Björklund A. Fruit and vegetable intake and risk of prediabetes and type 2 diabetes: results from a 20-year long prospective cohort study in Swedish men and women. Eur J Nutr. 2022;61(6):3175-3187.

27. Christensen AS, Viggers L, Hasselström K, Gregersen S. Effect of fruit restriction on glycemic control in patients with type 2 diabetes--a randomized trial. Nutr J. 2013;12:29. Published 2013 Mar 5. doi:10.1186/1475-2891-12-29.

28. Butler AE, Obaid J, Wasif P, Varghese JV, Abdulrahman R, Alromaihi D, Atkin SL, Alamuddin N. Effect of Date Fruit Consumption on the Glycemic Control of Patients with Type 2 Diabetes: A Randomized Clinical Trial. Nutrients. 2022 Aug 25;14(17):3491.

29. Bryce R, WolfsonBryce JA, CohenBryce A, et al. A pilot randomized controlled trial of a fruit and vegetable prescription program at a federally qualified health center in low income uncontrolled diabetics. Prev Med Rep. 2021;23:101410.

30. Chandalia M, Garg A, Lutjohann D, von Bergmann K, Grundy SM, Brinkley LJ. Beneficial effects of high dietary fiber intake in patients with type 2 diabetes mellitus. N Engl J Med. 2000 May 11;342(19):1392-8.