Weight loss was 9.7 pounds (4.4 kg) in the vegan group and 6.6 pounds (3.0 kg) in the ADA group.
HbA1c declined 0.34 point in the vegan group and 0.14 point in the ADA group.
Before any changes in lipid-lowering medications, total cholesterol decreased by 20.4 mg/dL (0.53 mmol/L) in the vegan group and 6.8 mg/dL (0.18 mmol/L) in the ADA group, and LDL cholesterol decreased by 13.5 mg/dL (0.35 mmol/L) and 3.4 mg/dL (0.09 mmol/L) in the vegan and conventional groups respectively.
Interestingly, the study participants rated the vegan and ADA diets as being equally acceptable.
Several additional reports from the PCRM team were released between 2014 and 2018. In 2014, a systematic review and meta-analysis of vegetarian diets and glycemic control in diabetes showed vegetarian diets produced a significant 0.39 point reduction in HbA1c and a nonsignificant reduction in fasting blood glucose of 0.36 mmol/L (6.5 mg/dL).
A 2015 twenty-week pilot study reported significant improvements in diabetic neuropathy with a low-fat vegan diet.
In 2018, significant improvements in beta cell function and insulin sensitivity were reported in overweight adults with no history of diabetes.
Prior to joining the PCRM team as director of clinical research, the lead author of this study, Hana Kahleova, MD, conducted a number of trials using plant-based diets in the treatment of diabetes in the Czech Republic. The first, a 2011 study, randomized seventy-four participants with diabetes to a vegetarian diet or a conventional diabetic control diet with the same number of calories.
The vegetarian diet contained about 60 percent of energy from carbohydrate, 15 percent protein, and 25 percent fat, while the conventional diabetic diet provided about 50 percent carbohydrate, 20 percent protein, and 30 percent fat (7 percent or less saturated fat and less than 200 mg cholesterol a day). One portion of low-fat yogurt was the only animal product permitted in the diet.
In the intervention group, 43 percent of participants reduced diabetes medications compared to 5 percent in the control group. Intervention participants dropped 13.6 pounds (6.2 kg) compared to 7 pounds (3.2 kg) in the control group and had greater losses in visceral fat. The vegetarian group also had better improvements in insulin sensitivity, markers of inflammation, oxidative stress, and blood lipids.
In 2013, Kahleova’s team reported improved quality of life, mood, and eating behavior with a vegetarian diet.
A 2014 trial comparing vegan meals with meat-rich meals containing the same calories found that the meat meal was accompanied by an impaired gastrointestinal hormone response and increased oxidative stress.
A novel 2016 study compared the effects of low-calorie vegetarian versus conventional diabetes diets on physical fitness in people with diabetes.
Maximal oxygen consumption (VO 2 max) increased by 12 percent in the vegetarian group, whereas no significant change was observed in the conventional diet group. Maximal performance (watt max) increased by 21 percent in the vegetarian group but was unchanged in the conventional diet group.
A second novel trial released in 2017 examined the effects of low-calorie vegetarian versus conventional diabetes diets on thigh adipose (fat) tissue distribution in participants with diabetes.
Greater reduction was observed in total leg area and in intramuscular fat in participants consuming the vegetarian diet.
Only those consuming the vegetarian diet experienced a significant reduction in subfascial fat (the type of fat that lines our muscles).
Participants on the vegetarian diet also had more favorable changes in HbA1c, fasting plasma glucose, and beta cell insulin sensitivity.
In 2019, a study involving sixty men (twenty with diabetes, twenty obese, and twenty healthy) reported favorable effects on gut hormones and satiety in those eating a vegan meal with tofu compared with a meat-and-cheese-based meal matched for energy and macronutrients.
A Korean research team measured glycemic control in patients with diabetes on a carbohydrate-rich vegan diet compared with a control group on a conventional diabetic diet.
The vegan diet consisted of whole grains (predominantly brown rice), vegetables, fruits, and legumes, along with a selection of foods that don’t spike blood sugar levels (green vegetables and seaweed). The conventional mixed diabetic diet provided 50, 60 percent carbohydrate, 15, 20 percent protein, less than 25 percent fat, less than 7 percent saturated fat, minimal trans-fat intake, and 200 milligrams or less per day of cholesterol.
HbA1c levels decreased by 0.5 percentage point in the vegan group compared with 0.2 percentage point in the conventional group.
When the analysis was restricted to participants who were highly adherent to their respective diets, HbA1c dropped 0.9 percentage point in the vegan group and 0.3 percentage point in the conventional diet group.
The inclusion of individuals older than age sixty in this trial, and in the majority of vegetarian trials mentioned in the meta-analysis above, supports recommending plant-based diets to all age groups with diabetes, including older adults.
The authors concluded that both diets led to reductions in HbA1c levels; however, glycemic control was better with the vegan diet than with the conventional diet.
They recommended that dietary guidelines for patients with type 2 diabetes should include a vegan diet for better management and treatment.
A 2016 review published in Canadian Journal of Diabetes reported that plant-based diets are best for people with diabetes.
Researchers reviewed thirteen studies that explored the efficacy and acceptability of plant-based diets as treatment for diabetes.
Diabetes patients who followed a plant-based diet improved their insulin sensitivity, reduced their diabetes medications, and lowered their intakes of saturated fat and cholesterol.
Results also showed high acceptance rates and, as a result of decreased meat consumption, lower disease prevalence among those who followed a plant-based diet.
The research team called on clinicians to provide more frequent and standardized nutrition education and support for plant-based diets as diabetes treatment.
In 2017, an American review of plant-based diets in the prevention and treatment of diabetes was published. In this report, plant-based diets are defined as eating patterns that emphasize legumes, whole grains, vegetables, fruits, nuts, and seeds and discourage most or all animal products.
The authors provide evidence from observational and interventional studies demonstrating the benefits of plant-based diets in treating and reducing key diabetes-related macrovascular and microvascular complications. They suggest that the focus of the diet should be on overall eating patterns while including unrefined versus refined carbohydrates, monounsaturated and polyunsaturated versus saturated and trans fats, and plant rather than animal protein. They also thought the best way to highlight the advantages of a plant-based diet would be to underscore its benefits: the promotion of a healthy body weight, increased intake of fiber and phytonutrients, improved food, microbiome interactions, and decreased intake of saturated fat, advanced glycation end products (see page 76 ), nitrosamines (a possible carcinogen), and heme iron (a form of iron associated with heart disease).
Three reviews that looked at plant-based diets in the prevention and treatment of diabetes were released in 2018.
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The first review, from the United States, concludes that health-care providers should feel confident in recommending a vegetarian diet to patients who have prediabetes or diabetes.
However, they clearly distinguish between healthful and unhealthful plant-based diets. The use of diets rich in whole grains, fruits, vegetables, nuts, legumes, and unsaturated fats are advised, while the use of diets containing higher amounts of refined grains, added sugars, and saturated fats are cautioned against. The authors add that there is evidence that a healthful vegan diet has the greatest therapeutic value, especially for reducing fasting blood glucose levels and reducing the risk of complications, such as cardiovascular disease.
The second review, from Indonesia, concludes that in patients with diabetes, HbA1c reduction is greater in those consuming plant-based diets compared with patients consuming a conventional diet.
The third review was a meta-analysis of eleven studies and 433 participants with diabetes.
Eight of the trials reported on vegan diets and three on vegetarian diets. In six of the studies, patients reduced or discontinued medications used to treat diabetes or symptoms of diabetes. Participants reported improvements in blood glucose levels as well as blood cholesterol levels. They also experienced improvements in physical health and mental health. Nerve pain diminished, depression levels dropped, and overall quality of life was enhanced.
In 2006, I had the privilege of serving as the lead dietitian on a diabetes lifestyle research project in the Republic of the Marshall Islands (RMI), which lies about 2,300 miles southwest of Hawaii. The project was funded by the United States and was a joint venture of the RMI Ministry of Health and Canvasback Missions, Inc.
In several countries of the South Pacific, the prevalence of diabetes among adults is in the range of 25, 33 percent. The RMI has the highest prevalence of diabetes in the world, with 32.9 percent of all adults being affected.
A century ago, when people lived off the land and sea and were slim and physically active, diabetes was virtually unheard of.
The Marshallese diet consisted of edible plants, such as coconut, breadfruit, taro, pandanus, bananas, and leafy greens, along with fish and other seafood.
In the 1950s, only three people in the RMI were known to have the disease.
By the 1990s, the prevalence had reached 30 percent, and now more than half of all hospital admissions in the capital city of Majuro are due to diabetes and its complications.
Today, the majority of Marshallese are sedentary and live predominantly on imported, processed foods.
A typical adult’s breakfast consists of cake donuts or sweet pancakes and coffee, while children often start the day with popsicles, chips, soda pop, sweet cereal, or dry ramen noodles with Kool-Aid powder sprinkled on top for extra flavor.
Lunch and dinner feature sticky white rice with meat or fish.
Favorite meats are Spam, canned corned beef, grilled chicken, and variety meats, such as turkey tails.
Meals are often washed down with a sweetened beverage.
It would be difficult to design a diet that could more efficiently induce diabetes than the diet that has been adopted by the Marshallese people.
Our team conducted a randomized controlled trial with five groups and a total of 169 participants.
We compared an intensive diet-and-lifestyle program with conventional treatment for type 2 diabetes.
One group followed a whole-foods, plant-based diet that was high in fiber, antioxidants, and phytochemicals (the protective substances in plants).
They also received daily education about nutrition and lifestyle, including shopping tours, cooking classes, and instruction in growing vegetables to keep food costs down.
Participants took part in one-hour fitness classes at least four times a week, walked after each meal, and were encouraged to do strength and flexibility exercises at home.