Several plant foods, such as whole grains, fruits, and vegetables, are associated with a lower risk of T2D (1), while certain animal foods, such as red and processed meats, are positively associated with T2D risk (2).
People in North America that follow any form of vegetarian diet have a lower risk of type II diabetes, with vegans having the lowest risk. This is regardless of age, gender, education, income, television watching, physical activity, sleep, alcohol use, smoking and BMI (3).
These findings are from observational studies and therefore cannot provide concrete evidence, however they can provide clues to evidence.
A number of randomised control trials have been carried out to study the effects of plant-based diets on blood sugar control.
A 12-week study provided one group of type II diabetics with a vegan diet with whole grains, while the control group were told to follow a conventional diabetic diet (4). The conventional diet was low in fat and consisting of both plant and animal foods. After 12 weeks both groups significantly reduced their HbA1c levels but the reduction was greater in the group that followed the vegan diet (4).
A longer-term study was also carried out to assess the benefits of plant-based diets in people with poor metabolic health (5). One group received usual care advised by government guidelines while the other group received usual care alongside a plant-based diet for 12 months.
There were no limitations on calorie intake and there was no mandatory exercise. The plant-based group reduced their BMI by 4.2 after 12 months, while there was no change in the control group. HbA1c significantly decreased in the intervention group, while there were no differences in the control group. The people in the plant-based group also reported an improved quality of life and a reduction in medication use (5).
Beta Cell Function
Further research suggests that plant-based diets improve blood sugar by improving beta-cell function, which leads to an increase in insulin release in response to a meal. A study looked the effects of a plant-based diet on beta-cell function and insulin sensitivity (6).
38 type II diabetics were told to follow a plant-based diet for 16 weeks, while 37 type II diabetics were told to follow their current mixed diet. After 16 weeks, there was an increase in insulin secretion and insulin sensitivity in the plant-based group. BMI and body fat was only reduced in the plant-based group (6), which may explain the findings.
Substituting red meat with legumes has shown to improve blood sugar control and normalise cholesterol levels in type II diabetics despite being calorie-matched (7). These benefits may be due to fibre and phytochemicals that cannot be obtained from animal foods.
Plants-based diets are typically lower in vitamin B2 and B12 so supplementing may be required. Also, the absorption of calcium and iron is lower in plant foods. However, iron absorption can be increased by consuming iron-rich foods alongside vitamin C-rich foods (8). It is important to meet your vitamin D requirements, which is needed for enhancing calcium absorption.
Plant-based diets are also lower in the omega-3s, DHA and EPA, which are important for brain and eye functions, and cardiovascular health. Plants foods contain the omega-3 alpha-linolenic acid, which can be converted into EPA and DHA but the conversion rate is very low. However, DHA can be obtained from microalgae supplements (9). Therefore, if you decide to follow a plant-based diet then you should carefully plan your meals and supplements to prevent nutrient deficiencies.
The research indicates that a plant-based diet can be used as an effective way for managing type II diabetes. This is likely due to several healthful foods such as whole grains, fruits and vegetables which are high in fibre and phytochemicals. Fruits and vegetables also have a lower calorie density (lower in fat, higher in fibre and water) than animal foods, which can help with fat loss.
It is important to stick to whole and minimally processed foods because refined grains and sugar-sweetened beverages can be consumed on a plant-based diet but are associated with an increased risk of type II diabetes (10,11). This is highlighted in a study published in the PLOS Medicine journal, which found that a healthy plant-based diet markedly reduced diabetes risk compared to a non-vegetarian diet. However, a plant-based diet that was high in less healthy foods slightly increased the risk (12).
Micronutrients are also lost during the refining process of carbohydrates, which is another reason to consume predominantly whole foods. A plant-based diet requires careful meal planning and supplementation to prevent micronutrients deficiencies.
Even if you decide not to follow an exclusively plant-based diet, increasing plant-food consumption and lowering animal food intake will be beneficial for controlling your blood sugar levels.
- Cooper AJ, Forouhi NG, Ye Z, Buijsse B, Arriola L, Balkau B, Barricarte A, Beulens JW, Boeing H, Büchner FL, Dahm CC. Fruit and vegetable intake and type 2 diabetes: EPIC-InterAct prospective study and meta-analysis. European journal of clinical nutrition. 2012 Oct;66(10):1082.
- Micha R, Michas G, Mozaffarian D. Unprocessed red and processed meats and risk of coronary artery disease and type 2 diabetes–an updated review of the evidence. Current atherosclerosis reports. 2012 Dec 1;14(6):515-24.
- Tonstad S, Stewart K, Oda K, Batech M, Herring RP, Fraser GE. Vegetarian diets and incidence of diabetes in the Adventist Health Study-2. Nutrition, Metabolism and Cardiovascular Diseases. 2013 Apr 1;23(4):292-9.
- 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 2;11(6):e0155918.
- Wright N, Wilson L, Smith M, Duncan B, McHugh P. The BROAD study: A randomised controlled trial using a whole food plant-based diet in the community for obesity, ischaemic heart disease or diabetes. Nutrition & diabetes. 2017 Mar;7(3):e256.
- Kahleova H, Tura A, Hill M, Holubkov R, Barnard ND. A Plant-Based Dietary Intervention Improves Beta-Cell Function and Insulin Resistance in Overweight Adults: A 16-Week Randomized Clinical Trial. Nutrients. 2018 Feb 9;10(2):189.
- Hosseinpour-Niazi S, Mirmiran P, Hedayati M, Azizi F. Substitution of red meat with legumes in the therapeutic lifestyle change diet based on dietary advice improves cardiometabolic risk factors in overweight type 2 diabetes patients: a cross-over randomized clinical trial. European journal of clinical nutrition. 2015 May;69(5):592.
- Kristensen NB, Madsen ML, Hansen TH, Allin KH, Hoppe C, Fagt S, Lausten MS, Gøbel RJ, Vestergaard H, Hansen T, Pedersen O. Intake of macro-and micronutrients in Danish vegans. Nutrition journal. 2015 Dec;14(1):115.
- Craig WJ. Health effects of vegan diets–. The American journal of clinical nutrition. 2009 Mar 11;89(5):1627S-33S.
- Hu EA, Pan A, Malik V, Sun Q. White rice consumption and risk of type 2 diabetes: meta-analysis and systematic review. Bmj. 2012 Mar 15;344:e1454.
- Malik VS, Popkin BM, Bray GA, Després JP, Willett WC, Hu FB. Sugar sweetened beverages and risk of metabolic syndrome and type 2 diabetes: a meta-analysis. Diabetes care. 2010 Aug 4.
- Satija A, Bhupathiraju SN, Rimm EB, Spiegelman D, Chiuve SE, Borgi L, Willett WC, Manson JE, Sun Q, Hu FB. Plant-based dietary patterns and incidence of type 2 diabetes in US men and women: results from three prospective cohort studies. PLoS medicine. 2016 Jun 14;13(6):e1002039.