Vegetarian, vegan, plant-based – what’s the difference? For most of us, not much. But the medical community sees distinctions because of the growing body of evidence linking diet and health.

As a writer, I find “plant-based” to be a handy synonym for “vegetarian” and “vegan” and often use the three terms interchangeably. As a clinician, Dr. Mary Harkins Becker of Yarmouth accords the three terms distinct meanings.

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Following a bout of my more cavalier use of “plant-based” in my columns, Becker dropped me a note suggesting I clarify the concept from a medical perspective for my readers.

She told me she was “impressed with the data on disease prevention and reversal with a plant-based diet.” She went on to say, “The diet is noted for being about 10 percent protein and 10 percent fat and … differs from vegan or vegetarian diets in that it is quite low in fat, protein and processed food.”

Becker, who practices emergency and palliative medicine at Maine Medical Center in Portland, closed her letter by pointing out “no other diet has been shown to reverse heart disease and slow and stop tumor growth in mammalian studies.”

I decided to investigate further, and what I discovered is a plant-based diet that follows the findings of clinical studies can be vegetarian or vegan, but that a vegan diet or a vegetarian diet are not always plant-based. Confused yet? Let’s take a closer look.

PLANT-BASED SCIENCE

An early, well-known trial in the field of plant-based medicine is the Lifestyle Heart Trial carried out by Dr. Dean Ornish and published in 1990 in the journal Lancet, with a 1998 follow-up in the Journal of the American Medical Association.

In this randomized study, Ornish and his team found that 82 percent of heart disease patients who followed the prescribed diet for a year saw improvements in the health of their veins.

The study authors don’t use the term “plant-based” (likely since this study was conducted before the term was popularized) and instead describe the diet in journal articles as a “10 percent fat whole foods vegetarian diet” where patients were advised “to avoid simple sugars and to emphasize the intake of complex carbohydrates and other whole foods.”

These days, the diet Ornish is known for recommending is often called a plant-based diet that includes limited fat-free dairy and egg whites. Those following his recommended diet generally avoid oils, nuts, seeds, coconuts and avocados because of their high fat content. The diet also steers clear of highly processed foods.

In more recent dietary studies, the term “plant-based” shows up often. For instance, a randomized workplace trial known as the GEICO Study, published in the European Journal of Clinical Nutrition in 2012, found that after 18 weeks participants following a low-fat plant-based diet lost an average of 9.48 pounds, dropped 13 points off their LDL cholesterol score and lowered their biochemical markers for Type 2 diabetes.

The study authors also refer to the diet as low-fat vegan and report that the GEICO cafeterias served special vegan meals for participants that included “oatmeal, minestrone or lentil soup, veggie burgers and portobello mushroom sandwiches.”

One of the most recent studies related to heart disease and diet was published in 2014 in The Journal of Family Practice. Carried out at the Cleveland Clinic in Ohio, the study found a plant-based diet without “dairy, fish, and meat, and added oil” reduced coronary artery disease symptoms in 94 percent of patients and reversed the disease in 22 percent.

A particularly comprehensive definition of “plant-based” shows up in a 2013 review of plant-based dietary studies published in The Permanente Journal.

In the article the researchers wrote: “A healthy, plant-based diet aims to maximize the consumption of nutrient-dense plant foods while minimizing processed foods, oils and animal foods (including dairy products and eggs). It encourages lots of vegetables (cooked or raw), fruits, beans, peas, lentils, soybeans, seeds and nuts (in smaller amounts) and is generally low fat.”

While these clinically tested plant-based diets are not identical, they share an emphasis on plant foods in a minimally processed state. They tend to avoid added oils, sugars and white flour. As a result, this way of eating is often called a whole-foods, plant-based diet to distinguish it from a broader plant-based diet, which technically could include any food derived from plants, including french fries and vegan cake.

After reviewing the medical studies, I was curious to learn how local physicians interpret this information for patients.

PLANT-BASED MEDICINE

I caught up with cardiologist Dr. Jeffrey Rosenblatt while he was doing rounds on the busy cardiac unit at Maine Medical Center. He told me that “when we prescribe or talk about a nutritional approach to feed your body we’re talking about a plant-based diet.”

He said this diet could be, but isn’t necessarily, the same as a vegan diet. In addition, he pointed out that the word “vegan” encompasses a nonviolent philosophy that goes beyond what people eat and means avoiding things such as leather and cosmetics that are tested on animals.

“You can still wear a leather belt on a plant-based diet,” Rosenblatt said and added some patients might say, “I have a vegan diet but I’m not a vegan.”

Rosenblatt agreed with Becker that just like the word “vegan,” the more generic term “vegetarian” doesn’t always mean healthy, saying “you can call yourself a vegetarian and live on grilled cheese sandwiches, pickles and potato chips and be infinitely more malnourished and unwell than (someone eating) any animal-based diet.”

Dr. Reuben Bell, who practices family medicine at the True North Health Center in Falmouth and frequently talks with patients about food, agreed the term “vegetarian” is broad.

“A working definition of a vegetarian is a person who simply doesn’t eat meat,” Bell said. “They usually eat milk products, eggs and plants. But if you want to break that down into a term you’d see in a scientific study, that would be called a lacto-ovo vegetarian.”

Bell added that the word “vegan,” particularly when it includes “animal rights and a save-the-planet agenda,” can be off-putting to some people.

Even though the term “vegan” can carry cultural baggage and isn’t always the same as a clinically tested plant-based diet, Bell prefers “vegan” rather than “plant-based” when talking with patients. He feels it is more easily understood, since “vegan” is used more regularly on menus, food labels and in the media.

When talking to patients about improving their diet, Bell asks them to “imagine two opposite poles with a spectrum in between. One pole is the standard American diet with lots of fried meat and starch. The other pole is just plants and that’s called a vegan diet. I say, ‘you fall somewhere between those poles.’ I tell them for health purposes ‘start moving toward that vegan pole.’ ”

Bell said a plant-based diet isn’t always vegetarian, and points to a plant-based macrobiotic diet that “is mostly plants but would at times involve a little fish.”

Rosenblatt agreed that a plant-based diet can include animal products.

“In a plant-based medical research protocol you do not typically see any meat or any cheese,” Rosenblatt said. “But in the real world, I do mention to people that they don’t have to (completely avoid) animal products. However, I do really steer people away from red meats.”

A patient recently asked Bell what is wrong with eating meat.

“I told him when you eat meat, milk or eggs the problem is your immune system is stimulated to some degree by these proteins,” Bell said. “I don’t know why. It may have something to do with how close we are in the phylogenetic tree. These proteins get into the immune system and set up a mild degree of inflammatory reaction. That produces certain chemical products that over time have a deleterious effect.”

These days Rosenblatt finds patients increasingly open to making the significant dietary changes required to move from eating typical American food to a whole-foods, plant-based diet.

Yet he points out barriers remain, including physicians who are unfamiliar with the science and hospitals that serve “a cheeseburger with a white bread bun and a bag of baked potato chips and an 8-ounce Coca-Cola” to patients who’ve had a heart attack.

He encountered another example of a barrier to better eating earlier in the day I spoke with him. Rosenblatt was on hold with an insurance company when a recorded health tip told him his diet should include “6 ounces of lean meat every day.”

“That’s a recommendation that is not well-based in scientific fact,” Rosenblatt said.

Meanwhile, our dieting-obsessed culture churns out a lot of food fads and unreliable nutrition information that can be confusing to patients trying to use diet to reverse disease.

Because of this, Rosenblatt said physicians have an obligation to stay up to date on the latest studies linking plant-based nutrition and health.

“The health care provider has to have a role in translating this for a patient,” Rosenblatt said.

As a writer, I’ll aim to do a better job translating these terms for my readers.

Avery Yale Kamila is a freelance food writer who lives in Portland. She can be reached at:

avery.kamila@gmail.com

Twitter: AveryYaleKamila