In mid-July 2021 researchers with the Physicians Committee for Responsible Medicine reviewed the literature for evidence of the effect of diet on type-2 diabetes prevention and treatment. (1) Their research showed that eating patterns emphasizing fruits, vegetables, legumes and whole grains and removing animal products improve the risk factors for diabetes including blood sugar levels, cholesterol levels, blood pressure, body weight and risk of cardiovascular disease. In addition, the need for medication to control blood sugar can be greatly reduced or disappear altogether. This is nothing new, however. Decades of scientific literature have confirmed over and over again that diets consisting of mainly plants are a powerful weapon in the prevention and reversal of type-2 diabetes. Let’s look at this evidence.
Reducing the Risk of Type-2 Diabetes
Note: The 2021 review (1) uses the term “plant-based” for diets consisting predominantly of grains, vegetables, legumes, fruits, nuts, seeds, and products made from them. This term includes vegetarian diets (which exclude meat) and two subset vegetarian diets, lacto-ovo vegetarian diets (which include dairy products and eggs) and vegan diets (which exclude all animal products).
An omnivorous diet is one that includes food sourced from both animals and plants.
The 2021 review mentioned in the introduction illustrated that eating plant-based reduces risk of type-2 diabetes while eating meat (including poultry) increases this risk. Here are some of its findings (1).
- Analysis of the Adventist Health Study-2 revealed that, when compared to non-vegetarians, vegans had a 77% reduction in the risk of developing type-2 diabetes and lacto-ovo vegetarians had a 54% reduction in the same risk. This lowering of risk appears to be the result of avoiding animal-derived food products and was independent of the diets’ beneficial effects on body weight.
- A study from Harvard that included participants from the Health Professionals Follow-Up Study, the Nurses’ Health Study, and the Nurses’ Health Study II discovered that increasing meat by only half a serving a day was associated with a 48% increase in type-2 diabetes risk over four years.
- The Tzu Chi Health Study from Taiwan found significant reductions in type-2 diabetes risk among vegetarian Buddhists. Compared with Buddhists eating an omnivorous diet, the vegetarian Buddhists had a 51% lower risk of developing diabetes in men and a 75% lower risk in postmenopausal women after controlling for BMI (Body Mass Index) and other lifestyle factors. Note that omnivores in this population consume relatively little meat or fish by Western standards while the vegetarian group consumes more soy products, green leafy vegetables, nuts and whole grains; less tea; and similar amounts of dairy products and fruits compared to the omnivores.
- Plant-based eating improves body weight, insulin sensitivity and the function of the cells of the pancreas that make insulin, all key underlying factors in the development of type-2 diabetes.
Treatment of Type-2 Diabetes
Plant-based diets, especially vegan diets, can play a large role in the treatment of type-2 diabetes. They improve blood sugar control, reduce A1C levels (the average blood sugar level over the preceding 3 months), improve body weight and lower cardiovascular risk factors. Plant-based diets regularly result in reductions in the dose of medications or insulin needed to control blood sugar and in discontinuing these therapies altogether. (1)
The review also notes that plant-based eating patterns outperform other dietary approaches for treating type-2 diabetes such as bariatric surgery, very-low-calorie diets, low-carbohydrate diets, Mediterranean diets and the DASH Diet (Dietary Approaches for Stopping Hypertension). (1)
Additionally, plant-sourced diets are beneficial in reducing the complications of type-2 diabetes, including cardiovascular disease, chronic kidney disease, neuropathy (dysfunction of nerves including numbness, pain and weakness caused by high blood sugar levels) and diabetic retinopathy (blood vessel damage in the eye due to high blood sugar levels that impairs vision and progresses to blindness). (1)
A study from the UK in 2018 had similar findings. Researchers reviewed eleven controlled trials on dietary interventions for type-2 diabetes and found consistent evidence that plant-based diets are the most efficient dietary plan for the promotion of overall health and quality of life in type-2 diabetes patients. Compared to control groups eating an omnivorous diet or a diet recommended by a national diabetes association, eating plant-based is associated with lower A1C levels, better weight control and lower total and low-density cholesterol along with significant improvements in emotional well-being, depression, triglyceride levels and in the neuropathic pain caused by uncontrolled blood sugar in diabetes. Furthermore, adherence to eating a plant-based diet was high compared to that of the control groups. This suggests high rates of acceptability of eating plant-based among the participants of the intervention groups. (2)
Potential Mechanisms for the Benefits Offered by Plant-Based Eating to Type-2 Diabetes
Plant-based eating patterns reduce insulin resistance (1)
Insulin resistance happens when the body does not respond to the hormone, insulin, so that the glucose (sugar) in the bloodstream cannot enter the cells where it is needed for energy. The result is high blood sugar levels. It is caused by the accumulation of fats within muscle and liver cells, a situation that is highly responsive to changes in the diet. Most plant-sourced foods are inherently low in fat. The effects of dietary fat on blood sugar can be observed not only after long-term consumption of a high-fat dietary pattern. Elevated blood sugar levels occur even after consuming only one fatty meal and they can remain significantly high for hours after that meal.
Plant-based eating can protect the intestinal barrier (1)
The lining of the gastrointestinal tract acts as a semipermeable barrier that allows the absorption of nutrients into the blood while at the same time preventing the transport of potentially harmful toxins and microorganisms across the barrier and into the bloodstream. Diets high in fat can disrupt this normal intestinal protective layer.
Plant-based eating patterns encourage a healthy body weight (1)
Weight management is important in improving sensitivity to insulin and blood sugar control. Eating plant-based has proven to be a very effective way to manage weight. Randomized trials show that consuming plants results in greater weight loss than when eating diets containing animal products. In addition, much of the fat that is lost comes from visceral fat (fat located in the abdomen that surrounds important body organs, causing inflammation and metabolic disturbances) which has the additional health advantages of reducing inflammation and insulin resistance. The weight loss that occurs with plant-based eating patterns is attributable to increased fiber and carbohydrate intake as well as to reduced fat intake, both resulting in a reduction in the energy density of the diet. Moreover, plant-based eating increases the thermic effect of food (the after-meal burn of calories). Surprisingly, diets used in these studies did not restrict portion sizes and participants reported that they were not hungry between meals.
Plant-based eating patterns improve the function of beta-cells (1)
Beta-cells are the cells in the pancreas that produce insulin. Randomized trials have shown that insulin secretion increases markedly while eating a low-fat plant-based diet when compared to controls eating their regular meal choices. Such studies demonstrate the potential of eating plants in the reversal of beta-cell dysfunction and insulin resistance in patients with type-2 diabetes.
Plant-based eating patterns stimulate secretion of hormones that influence blood sugar (3)
Gastrointestinal hormones such as incretins and amylin are released from the small intestine after meals to help in the production and action of insulin, the balancing of blood sugar levels and the suppression of the appetite after eating. Lower secretion of incretins and insulin after eating is now recognized as one of the key mechanisms involved in the development of type-2 diabetes.
In 2019, a randomized crossover study compared two meals equal in energy, one vegan and one that included meat, and tracked the blood levels of glucose, insulin and other hormones in type-2 diabetics. Results showed that the blood sugar levels did not differ significantly between the two meals. However, the secretion of insulin as well as the actions of both insulin and incretin hormones were significantly enhanced after the vegan meal compared with the non-vegan meal. Amylin concentrations were also higher. In addition, several parameters of beta-cell function were improved. Researchers note that these effects have direct implications for the treatment of type-2 diabetes.
What Dietary Plans are Currently Being Recommended to Type-2 Diabetes Patients?
The results of the research we have looked at here as well as that from many other studies have shown that eating plant-based may be the most powerful way to control type-2 diabetes. But this is still contrary to much of the dietary advice presently being offered by diabetes associations around the world.
To point out a few, Diabetes Canada, the American Diabetes Association, the International Diabetes Federation and Diabetes Australia are all recommending similar dietary selections for the prevention and management of type-2 diabetes (4,5,6,7).
- Eating a wide variety of fruits and vegetables including legumes
- Eating whole grains
- Eating nuts and seeds
- Limiting processed foods including processed meats and fast foods
- Limiting red meats, added sugar, sugar-sweetened beverages, sweet baked goods, saturated fats and refined grains
- Choosing lean animal proteins (poultry without the skin or fish) with some suggestions for substitutions with protein sourced from vegetables
- Choosing low-fat dairy
- Choosing plant oils and nuts over animal fats
- Reducing weight and maintaining a healthy weight
In the past few years, Diabetes Canada and the American Diabetes Association have acknowledged that a completely plant-based diet is within the scope of their recommendations. But so far, national guidelines have not made it clear that eating only minimally processed plant-sourced foods and completely avoiding all animal-sourced foods is not only one of the dietary patterns that can be beneficial for type-2 diabetes, but is the one backed by science as having the greatest influence on both lowering the risk of developing type-2 diabetes and on its treatment and management.
In a recent article published in the BMJ (British Medical Journal) discussing the politics of nutrition, the authors state that dietary factors are of paramount importance in the prevention and treatment of type-2 diabetes. Yet they admit that controversy and confusion remain still. Among countries that offer dietary guidelines for the management of type-2 diabetes, recommendations have evolved from their previous focus on specific diets, such as low-fat or low-carb, to the recognition that a much more important consideration is the quality of the food being consumed. Furthermore, the notion that type-2 diabetes is irreversible has been unequivocally refuted. It is now well understood that the disease can be controlled and even reversed with prudent lifestyle alterations. These are signs of progress. But much more clarity is needed for the people who are suffering from type-2 diabetes. They should be informed about the power of everyday food choices for influencing the course of this disease. (8)
Here are some of the contentious issues to be overcome so that well-defined and easy to understand dietary guidelines can be created. (8)
- What is the healthiest proportion of each macronutrient (carbohydrates, proteins and fats) when it comes to type-2 diabetes management and prevention?
- What is the definition of a low-fat diet? The term “low-fat” has been used in research to describe diets containing such vague and varying fat levels of “less than 35%”, “a maximum of 20%” right down to “15% or less”.
- Which diet is better for weight loss – a low-fat diet or a low-carbohydrate diet?
- Should fish still be a recommended food in spite of the high probability that it is contaminated by chemicals such as methylmercury and polychlorinated biphenyls?
- Are any dairy products at all healthy, low-fat or high-fat, due to their possible contaminants such as dangerous microorganisms (bacteria and viruses), environmental pollutants (dioxins, furans, polychlorinated biphenyls and organochlorine pesticides) and hormones such as estrogen?
- Are isolated plant oils healthy (polyunsaturated and monounsaturated oils from plants, coconut oil, palm oil, olive oil) or should the recommendations for fat intake emphasize higher-fat whole plant foods such as avocados, nuts and seeds as a better source?
What is now required is high quality research focused on overcoming the limitations of some of the existing research, thereby resolving the areas of disagreement and misperception for countries wrestling with food guidelines. With new science in this area publishing almost daily, perhaps we are getting close to a time when guidelines for type-2 diabetics will provide clear and concise recommendations on what to eat and how to go about adopting a lifestyle transformation that can both prevent and reverse this devastating disease. (8)
1 Jardine, M.A., Kahleova, H., Levin, S.M., Ali, Z., Trapp, C.B., Barnard, N.D. Perspective: Plant-Based Eating Pattern for Type 2 Diabetes Prevention and Treatment: Efficacy, Mechanisms, and Practical Considerations. Advances in Nutrition. November 2021; 12(6): 2045–2055. Doi.org/10.1093/advances/nmab063
2 Toumpanakis, A., Turnbull, T., Alba-Barba, I. Effectiveness of plant-based diets in promoting well-being in the management of type 2 diabetes: a systematic review. BMJ Open Diabetes Res Care. Nov.2018; 6(2): 000534. Doi:10.1136/bmjdrc-2018-000534.
3 Kahleova, H., Tura, A., Klementova, M., et al. A plant-based meal stimulates incretin and insulin secretion more than an energy- and macronutrient-matched standard meal in type 2 diabetes: a randomized crossover study. Nutrients. 2019; 11: 486-497. Doi: 10.3390/nu11030486.
8 Forouhi, N.G,, Misra. A,, Mohan, V., Taylor, R., Yancy, W. Dietary and nutritional approaches for prevention and management of type 2 diabetes. BMJ 2018; 361:k2234. Doi:10.1136/bmj.k2234.
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