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Expert Critique

FROM THE ASCO Reading Room

Justin B. Echouffo Tcheugui MD, PhD Johns Hopkins University

Evidence has been accruing on the benefits of a vegan or plant-based diet (consisting of 10% fat, 15% protein, and 75% carbohydrates) for the management of diabetes. There is still however, a low rate of adoption of such a diet among patients. Even a partial adoption of plant-based eating patterns has been shown to provide benefits, reinforcing the need for improving the uptake among patients.

The benefits of a vegan diet among patients with type 2 diabetes are multiple. These include an improvement in HbA1c, fasting glucose, and fasting insulin levels, as well as in neuropathy-related symptoms. Compared with the more conventional low-fat, low-sugar diet, a vegan diet was associated with a reduction in the number of medications and an improvement in LDL-cholesterol, among people with diabetes. A plant-based diet has also been shown to significantly improve insulin resistance (as estimated by the measured by the Homeostasis Model Assessment index).

However, the adoption of a plant-based diet by patients remains a challenge, given its significant difference from their usual diet. The Academy of Nutrition and Dietetics has issued a position paper detailing the basics of a plant-based diet, including for patients with diabetes, which can serve as a guide for practitioners. Experts have postulated that if approached appropriately, the adoption may be easier than it seems. They argue that clinicians can achieve this by initiating the conversation about the change more often, to identify those interested in a plant-based diet. For those adopting a plant-based diet, it is of utmost importance to establish a structure, which is best done in conjunction with a dietitian or diabetes educator. This helps to set realistic expectations, manage the change process, and maximize adherence. Clinicians should however be aware that some plant-based diets can be unhealthy (if extremely rich in refined carbohydrates and fried foods). Plant-based diets can also lead to deficiency in vitamin B12. Hence, the need for a supervision by a nutritionist, especially given the risk of hypoglycemia at the start of a changeover, and the need for supplementing vitamin B12. It is also important for clinicians to bear in mind that patients who are not ready to fully embrace a plant-based diet can still derive some benefits from a partial adoption. However, it would be preferable for to encourage a full adoption, as this is associated with better outcomes.

Full Critique

Evidence continues to show that a vegan or plant-based diet holds tremendous benefits for patients with diabetes. The challenge, experts said, may be convincing patients to adopt that lifestyle and helping them properly maintain it.

A vegan diet for diabetes patients is generally defined as consisting of approximately 10% fat, 15% protein, and 75% carbohydrates, with vegetables, fruits, grains, and legumes the primary items consumed. No animal products -- including meat, dairy products, and eggs -- are part of a vegan diet. However, evidence shows that patients can still reap benefits with only a partial adoption of plant-based eating patterns.

Benefits

A scientific review published in May in the showed the range of improvements type 2 diabetes patients can achieve with a vegan diet. A 2015 study cited in the review found significant decreases in HgA1c levels (-0.15%), fasting glucose (-0.53%), and fasting insulin (-10 pmol/L) in patients who switched 35% of their daily protein from animal sources to plant sources. In another study cited, 81% of patients resolved their burning neuropathy after spending 25 days on a plant-based diet.

"A plant-based diet is really one-stop shopping from a health perspective," said paper co-author Michelle McMacken, MD, an assistant professor at NYU School of Medicine and director of the Bellevue Adult Weight Management Program in New York. "It is really extraordinarily effective in protecting against and treating diabetes, and we see this in a wealth of clinical trials."

A seminal 2006 study published in found that type 2 diabetes patients who followed a vegan diet fared significantly better than those who followed a more conventional low-fat, low-sugar diet based on American Diabetes Association guidelines. At the end of the study, 43% of the vegan patients reduced their diabetes medications compared with 26% of ADA dieters. HbA1c levels fell an average of 1.23 points for the vegan group compared with 0.38 points for the ADA group (P=0.01), and LDL cholesterol fell 21.2% in the vegan group versus 10.7% for the ADA group (P=0.02).

More recently, a study published February in found that patients' insulin resistance levels, as measured by the Homeostasis Model Assessment index, fell significantly (P<0.001) among participants who received a plant-based diet (treatment effect 1.0) (95% CI 1.2 to 0.8).

"Problems are caused by the accumulation of lipid particles, which come from fat, and a vegan diet doesn't have those particles," said Neal Barnard, MD, president of the Physicians Committee for Responsible Medicine, adjunct professor at the George Washington University School of Medicine and Health Sciences in Washington, D.C., and co-author of the 2006 study and the February study. "A vegan diet helps those particles to dissipate."

Creating and Managing Change

While the benefits are clear, it can still be difficult to persuade patients to adopt a plant-based diet, which in many cases may be significantly different from what a given patient is accustomed to.

Experts acknowledged that this can pose a challenge, but said it is easier than it may seem.

"It's a challenge to prescribe any change that's out of the norm," Barnard said. "But that doesn't mean it's difficult."

The conversation should begin with the physician, but need not be overly time-consuming.

"The doctor can spend at least a couple minutes talking about nutrition," Barnard said. "It doesn't need to be overly technical, but it needs to validate the idea. Then a dietitian can take over."

For a patient interested in adopting more plant-based eating habits, establishing a structure and working with a dietitian or diabetes educator helps create realistic expectations, manage the change process, and maximize adherence.

"People miss their meats, and the flavors of many foods," said Sandra Arevalo, a dietitian and administrator of nutrition services at Montefiore Medical Center in New York. "They say they want to be a vegan, but then say they don't like vegetables. But you talk about it like an adventure. You make one change at a time. First you get rid of red meats, then white meats, you replace them with beans, you bring in new foods and recipes, and you see how it goes."

Clinicians also should be aware that not all plant-based diets are created equal or automatically healthy. Patients who adopt vegan eating habits can still consume less-healthy items such as refined carbohydrates, fried foods, and juices while technically adhering to the diet. They can also lose key nutrients, such as vitamin B12, which can be difficult to get with plant-based foods.

"You should do it with some kind of professional help," Arevalo said. "You can have people doing it on their own but it can be poorly balanced and lack nutrients, because people don't know what to do."

McMacken advised close monitoring at the beginning of a changeover, as blood sugar can quickly drop, increasing the probability of hypoglycemia. There also are nutrients such as vitamin B12 that may have to be added through supplementation.

"Clinicians should become familiar with the basics of a plant-based diet," McMacken said. "They could even give it a try themselves. It's really important to not assume that patients are not open to this. At the same time, a patient who isn't ready to do it 100 percent can still do it part of the way."

Even if patients are not ready to fully commit to a vegan diet, Barnard favors encouraging the full adoption when talking with patients about the topic.

"It is not unlike a conversation about quitting smoking," he said. "You don't tell them to cut down, you tell them to quit. Some will quit and some will cut down, but if you say cut down, no one will quit."

A 2016 position paper from the outlines the key tenets of plant-based diets, including for patients with diabetes.