Can this natural diet help, or harm, your health?

There’s a food trend that’s sprouting up across health-conscious circles: plant-based diets. Today, more than a third of Americans report actively trying to eat more plant-based foods, according to a Nielsen Homescan survey. You can walk into virtually any grocery store and take your pick of plant-based meatless products, from fishless fish to “chik’n nuggets,” packaged by sought-after brands like Beyond Meat and Morningstar Farms. Even Burger King threw its hat in the ring, introducing its plant-based “Impossible Whopper” in 2019.

People embrace plant-based diets for all sorts of reasons, from health concerns, to ethics, to environmental sustainability. However, it’s important to point out that “plant-based” and “vegan” are different, despite that the terms are often used interchangeably. People who identify as vegan exclude all animal foods from their diets, including meat, seafood, poultry, eggs, dairy products, and even honey. Vegans also eschew any retail products made from animals, including leather shoes and fur coats. On the other hand, people who follow a plant-based diet typically aim to maximize their consumption of nutrient-dense plant foods such as vegetables, fruits, legumes, nuts, and seeds. Processed foods and animal products might remain in their diets, but typically in much lower quantities.

There is no one unifying definition of what constitutes a plant-based diet, and the definitions tend to change with time. Some experts recommend allowing animal products such as egg whites and skim milk in small amounts while others advocate avoiding animal-based products completely. As such, there is a great deal of confusion surrounding the diet, specifically when it comes to wading through all the plant-based products on store shelves. But the most important question of all: How can a plant-based diet help or hurt your health? Let’s look at the health benefits of a plant-based diet, as well as its inherent shortcomings.

Plant-based benefits

There’s evidence that chronic diseases, including obesity and cardiovascular disease, can be controlled, reduced, and possibly even reversed by adopting a plant-based diet. With an emphasis on whole plant foods, the diet increases the intake of several beneficial nutrients common in plants, particularly fiber and phytonutrients. A high-fiber diet has tons of benefits, including helping normalize bowel movements, lowering the risk of developing hemorrhoids, lowering LDL cholesterol, and controlling blood sugar levels. Phytonutrients—a term for a wide variety of compounds like antioxidants and flavonoids that are found only in plant foods—are under investigation, but preliminary evidence suggests they can help reduce inflammation, promote bone health, slow the growth of cancer cells, and slow the progression of Alzheimer’s disease by scavenging the free radicals that allow neurodegenerative disorders to advance.

Perhaps one of the most touted benefits of a plant-based diet is its ability to protect the heart. A study published in the Journal of the American College of Cardiology examined the dietary patterns of over 200,000 adults over 2 decades. Researchers found that those who followed a plant-based diet had the lowest risk for heart disease if they ate healthy plant-based foods (whole grains, fruits, vegetables, legumes, nuts, and healthy oils like olive oil) and avoided less healthy ones (refined grains, potato chips, white bread, and sugar-sweetened fruit juices). In comparison, those who ate a plant-based diet that included these less healthy foods didn’t lower their heart disease risk.  

“A moderate change in your diet, such as lowering your animal food intake by one to two servings per day and replacing it with legumes or nuts as your protein source, can have a lasting positive impact on your health," said the study’s lead author, Ambika Satija, ScD, in an interview with Harvard Men’s Health Watch.

More powers of plant-based food

Many proponents of plant-based diets are familiar with the landmark book The China Study, based on a sweeping population study of the eating and lifestyle habits of over 6,500 people in China. Results from the study suggest that following a plant-based diet is associated with a reduction in the risk of type 2 diabetes, heart disease, certain types of cancer (the study did not specify which types), and other chronic illnesses. Interestingly, the data suggested that these benefits increased proportionally with the percentage of a person’s diet that was plant-based.

A plant-based diet is also an effective strategy to counter obesity. In a 16-week randomized clinical trial, overweight participants were assigned to follow either a plant-based or a control diet. The plant-based diet proved more advantageous than the control diet in improving body weight, fat mass, and insulin resistance markers. Researchers pointed to two key reasons for this association: the quantity and quality of dietary plant protein in the diet improved body weight, composition, and insulin resistance, and a reduction of animal protein intake resulted in decreased fat mass.

While a plant-based diet is adequate in macro and micronutrients, many people question its ability to fulfill daily protein requirements. However, a study published in the American Journal of Nutrition found that all types of dietary protein—including those from plant sources—were equally sufficient in terms of meeting nutritional requirements.

“[P]ublic-health messages that encourage older adults to meet required protein intakes do not need to provide complicated recommendations about specific protein-containing foods,” the authors wrote. “Increased protein intake, regardless of the food source, will likely aid in the success of reaching required amounts.”

What’s more, getting your protein from plants instead of animals may even help you live longer, a study in JAMA Internal Medicine found. A cohort study that followed 70,000 Japanese adults found that higher intake of plant protein was associated with lower mortality. Substituting animal protein with plant protein also resulted in a lower risk of cancer-related and cardiovascular disease-related mortality.

Plant-based diet shortfalls

You might wonder whether Americans are interested in replacing meat with plants. But in fact, the US market for plant-based foods reached $5 billion in 2019.

With the growing popularity of plant-based eating, fresh new businesses are positioning themselves to supply products that meet increasing demand. From Beyond Meat’s “Beyond Burger” to Impossible Foods’ “Impossible Sausage,” these products are designed to look and taste like meat—but it’s not clear whether these plant-based products are healthier than the meaty foods they’re replacing. Such meatless products are heavily processed and contain high amounts of saturated fat, which is associated with increased risk of cardiovascular disease and mortality. They also tend to have large quantities of sodium, which increases the risk of high blood pressure when consumed in high amounts.

In a study carried out by researchers at the University of Oxford and published in The British Medical Journal, vegetarians and vegans had a higher risk of stroke, which researchers posited was due to low blood levels of total cholesterol and a low intake of certain vitamins. Plant-based foodies may run into some of these same risks. For example, people who eat exclusively whole-food plant-based diets have a slightly greater challenge in meeting adequate levels of dietary iron. Iron found in plant sources—such as black beans, spinach, raisins, oatmeal, and tomato juice—has a lower bioavailability than the iron in meat. However, iron deficiency is rare, even for individuals who follow a plant-based diet.

Vitamin B12, which is required for proper red blood cell formation and nerve function, is found most predominantly in animal products. People who maintain a strict plant-based diet are at greater risk for B12 deficiency, the consequences of which include fatigue, constipation, poor memory, and other neurological and psychiatric problems that “can progress if left untreated, and can lead to irreversible damage,” like delusions and memory loss, said Donald Hensrud, MD, MPH, director of the Mayo Clinic Healthy Living Program, in an interview with The New York Times.

In one case study, a patient with B12 deficiency developed numbness in his hands, had trouble walking, experienced severe joint pain, began turning yellow, and became progressively short of breath. While the damage can be lasting if left untreated, thankfully, most cases of B12 deficiency can be reversed easily with supplements or injections.

Plant-based eaters must also be sure to consume enough essential fatty acids, specifically omega-3 fats, which are found in plant sources such as ground flax seeds, walnuts, and canola oil. Deficiency in essential fatty acids can result in abnormalities in the skin, hair, and nails, like dry scaly rashes and poor wound healing. It can also cause decreased growth in infants and children, and increased susceptibility to infection. On the other hand, adequate intake of omega-3 fats is associated with a lower incidence of stroke.

Bottom line

Evidence consistently points to plant-based diets as having the ability to lower the risks for cancer, heart disease, type 2 diabetes, obesity, and other health conditions. And a position statement released by the Academy of Nutrition and Dietetics stated that vegetarian, vegan, and plant-based diets can be nutritious and healthful for people of all ages.

Anyone interested in adopting a fully plant-based diet should be aware of the nutrients that may be reduced when animal products are completely cut out. However, for those who plan to take a less strict approach to plant-based eating, nutritional deficiency will likely not be a problem.

When choosing one of the popular “meatless” substitutes at the grocery store, it’s important to read the ingredients. In general, if a lower risk of disease is your ultimate goal, it’s best to avoid these highly processed meat substitutes. Instead, select a legume-based product that showcases whole-food ingredients such as beans, grains, and seeds. 

To reap the benefits of a plant-based diet, people should aim to consume mainly fruits, vegetables, and legumes while avoiding unhealthy plant foods like white bread, white rice, fried potatoes, and sugary fruit juice, while minimizing consumption of meat, eggs, and dairy products. A healthy plant-based diet may require some planning and label-reading, but taking a diet-based approach to disease prevention will prove much simpler, more sustainable, and more enjoyable in the long run.