Plant-Based Diets Boast Many Health Claims, but What Does the Science Show?

Keeping tabs on the latest nutrition research is not for the faint of heart. Countless “facts” circulate on both social and traditional media, and many of these appear to be in conflict with each other. This seems particularly true for plant-based diets. Some headlines hail veganism as a cure for cancer, while others denounce plant-based foods as ultra-processed, unnatural and unhealthy. So which is it? Buckle up, it’s going to get a bit complicated. From diet trends to nutritional research, separating fact from fad can be challenging when it comes to what we eat. 

A note before we dig in: this article addresses how a plant-based diet can impact your personal health. The food on our plate has a wide range of impacts, however, including animals, climate, air, water, workers and more.

The Problem With Your Nutrition News

Most of the public learns of new nutrition research from the media. Health journalists are tasked with taking complicated research, and whittling it down to something that makes sense to the average reader. Some news outlets do this better than others, particularly science outlets or media outlets with a strong science-driven ethos.

Here’s an example of media coverage gone awry. A recent study published in one of The Lancet journals looked at how eating different categories of ultra-processed foods affects risk of heart disease and related risk of death.

Spoiler: the categories were very broad — plant-sourced ultra-processed foods included biscuits, breads, soda and chips and animal-sourced ultra-processed foods included meats, cheeses, eggs and milk.

Just how to define “ultra-processed” — and its health risks or lack thereof — has been fiercely debated in the last few years. When the study was covered by The Washington Post, Daily Mail and other outlets, each of these focused mostly on the angle of ultra-processed plant-based foods. The Daily Mail headline was especially egregious: “Vegan fake meats are linked to increase in heart deaths.”

As it turns out, plant-based meats were the lowest category of foods consumed in the study, making up only 0.5 percent of foods eaten, among other, technically plant-based foods like pastries, potato chips and soda. In other words, the study did not show that plant-based meats or other specific foods cause an increased risk of, well, anything, because of the broad category of foods consumed by participants in the study.

Though clicky headlines focus on risks associated with indulgence foods, research shows a range of health benefits from eating mostly plants. Eating a healthy, plant-forward diet can lower the risk of developing several major diseases and early mortality. A 2023 meta-analysis looked at 55 studies of more than two million participants, and found that a healthy plant-based diet is beneficial for preventing type 2 diabetes, cardiovascular disease, cancer and early mortality.

Plant-Based Diets Can Lower Diabetes Risk

One of the most common health claims associated with a plant-based diet is its effects on type 2 diabetes, ranging from lowering disease risk to an outright cure, which are two very different research questions.

First, a strong body of research does support the recommendation that a diet higher in plants and lower in animal products can help decrease your risk of developing diabetes. But before we go any further, let’s stay a minute on how researchers define “plant-based.”

The term plant-based in nutritional studies doesn’t always, or even often, mean a totally vegan diet. In fact, most research of people eating “plant-based” relies on what’s called the Plant-Based Index, a method for scoring what study participants eat to indicate eating more, or fewer, mostly whole plant foods.

OK, back to the research. One 2019 meta analysis looked at nine studies totaling more than 300,000 participants. The researchers found a link between eating a more plant-based diet, “especially those rich in healthful plant-based foods” and a lower risk of type 2 diabetes.”

Another study published this year followed 113,097 people over a 12-year period, and found that participants who ate a “healthful plant-based diet” — plant-forward or mostly plant-based and low in ultra-processed foods in this case — had a 24 percent lower risk of developing diabetes compared to those following a diet higher in sugary foods, refined grains and animal products. Participants following the high-sugar, meat-heavier diet had a 37 percent higher risk of developing the disease. (Note: spot those broad categories again. The higher-risk category ate red meat, but they also ate more added sugars and refined grains.)

Can eating plants help “reverse” diabetes? It’s possible, yes, but there’s some important nuance to mention here. One study that made the rounds in many vegan spaces last year found that “prescribing a high-fiber, low-fat, whole food, plant-predominant diet can facilitate lifestyle change and achieve remission of T2D” or type 2 diabetes. In this study, the prescribed diet allowed for five percent of calories from egg whites and dairy products.

Remission is possible, Dr. Matthew Nagra tells Sentient, but “fat loss is what drives diabetes remission,” and fat loss “is not specific to plant-based diets.” The researchers point this out in the study. The word “reverse” also isn’t quite accurate, Nagra says, as it’s possible for patients to become diabetic again. But “can a plant-based diet lead to remission of type 2 diabetes? Yes,” he says, “if it leads to significant body fat loss.” But other diets can also spur significant body fat loss too, including plant-rich diets that include some animal products.

What about a diet high in meat and saturated fat? Proponents of the carnivore diet also say that eating mostly meat with no plants has lowered their blood sugar. Dr. Darria Long Gillespie, clinical assistant professor at the University of Tennessee School of Medicine, told Healthline that at first glance, this result isn’t surprising. People who don’t consume any glucose will, of course, stabilize their blood sugar levels. But, Gillespie added, “there is more to diabetes than just your blood sugar level.” Eating an extremely meat-heavy diet with very large amounts of saturated fat can have “long-term health consequences.”

Ultimately, Nagra says that adopting a healthy plant-based diet “can help with management of blood glucose, and reduce the risk of long-term complications of a diabetes diagnosis, such as cardiovascular disease.” All in all, an excellent choice, Nagra says.

Eating a Plant-Based Diet is Good for the Heart

Perhaps one of the more straightforward health benefits of plant-based eating is heart health. A wide body of research shows that consuming a diet high in whole plant foods, such as vegetables, whole grains and legumes, can lower cardiovascular disease risk, reduce blood pressure, improve lipid profiles and have anti-inflammatory effects in the body.

In one 2023 review of studies ranging from 65 study participants to over 96,000, researchers found a link between a vegetarian or vegan diet and improved cardiovascular health as well as all-cause mortality. As is usually the case with observational studies however, it’s impossible to know if the health benefits were from an aspect of the diet or some other factor, and there were at least some studies in the review that included self-reported data (and humans are notoriously unreliable).

Meanwhile, the debate over the health risks of red meat consumption rages on, as some researchers argue the risks are overstated. This debate will likely never be settled, though there is a fair amount of consensus that eating high amounts of red meat raises health risks and eating low amounts would lower that risk.

Just as contentious is the debate over plant-based meat alternatives that have been categorized as “ultra-processed.” When compared to conventional meat, plant burgers and nuggets tend to come out on top, though there are caveats. Some plant-based burgers are healthier than others, and just as with red meat, the bulk of your diet matters more than the occasional indulgence.

One recent review, co-authored by Nagra, reviewed studies between 1970 and 2023 that compared plant-based to animal-based meats, nutritional profiles and impacts on cardiovascular disease risk factors. The researchers found that the makeup of plant-based meats did vary — an Impossible Foods patty contained six grams saturated fat, whereas a veggie burger from plant-based company Dr. Praeger’s contained just one gram, for instance. Still, on average, the authors concluded that plant-based meat alternatives tend to have more heart-healthy nutritional profiles compared to meat — including less saturated fat and more fiber per serving — all of which can improve cardiovascular risk factors.

A Plant-Based Diet Could Help You Live Longer, Or Not So Much

Thinking about your diet as a means to achieve longevity has become a popular trend, but is it accurate?

One such example, The Blue Zones Diet, gets its name from the regions where people are said to live longer than average. The diet, based on traditional and locally available foods, emphasizes plant-based options like whole grains, legumes and nuts, as well as moderate fish and dairy intake, limited meat and healthy fats. The recommendations are fairly similar to most healthy dietary guidelines, including government guides from Canada, Belgium and Sweden, as well as the Mediterranean Diet.

When it comes to the specific claim that eating a certain way will help you live longer however, the data is far less clear. For example, a 2022 review of Blue Zone longevity claims found plenty of limitations, including a lack of clear causation, diet variability over time, observational study constraints and other context-specific factors.

Last year, Oxford University researcher and longtime Blue Zone diet critic Dr. Saul Newman, called the diet “a feel-good grift that cherry picks other cultures to sell books.” Newman takes issue with the longevity claims in particular, going region-by-region to pick apart claims that there are more centenarians in these particular regions than others.

Nonetheless, the 2022 study authors called investigating the Blue Zones’ eating regimes and their historical evolution “an exciting field of study.” In other words, more research is needed, but safe to say that while dietary choices can certainly benefit your health in many ways, none guarantee a longer life.

Eating More Plants May Help Lower Alzheimer’s Risk

Alzheimer’s disease currently has no cure. But research suggests a number of lifestyle changes can lower risk of developing the disease — obesity, high blood pressure and lack of exercise all seem to increase risk.

One 2022 study published in the International Journal of Molecular Sciences found that a fully vegan diet may help prevent Alzheimer’s disease due to low saturated fat content, high phytonutrient content, like vitamins and antioxidants, and potential for preventing the breakdown of mood-regulating brain chemicals. But there was no way to assess whether strict veganism was more beneficial than vegetarianism or other diets, the authors noted, and a vegan diet could risk a B12 deficiency without supplementation.

Yet perhaps building on this promise, there is at least one trial where two dozen Alzheimer’s patients follow a regimen of many lifestyle changes, including a vegan diet. A majority of patients maintained their thinking skills during the trail, and some even improved. But of course, the trial covers a very small sample size deploying a number of lifestyle changes beyond diet, so quite a bit more research is needed.

Eating Plant-Based May Reduce Some Cancer Risk

Cancer is a complex disease, affecting different bodily systems in many different ways. Any claims suggesting there are ways to prevent all forms of cancer should be looked at carefully, and that goes for plant-based diets too.

That said, there are a number of promising studies showing some specific benefits. For example, a 2024 study of more than two thousand men diagnosed with nonmetastatic prostate cancer found a lower risk of disease progression for those eating a healthy plant-based diet, at least compared to participants eating a diet with much lower plant intake.

A small 2024 study found that women with stage 4 breast cancer who ate a healthy plant-based diet were more likely to lose weight and see beneficial changes to hormone levels, though whether these health measures actually slow cancer progression or reduce mortality was unclear. And diets with increases in dietary fiber and reductions in saturated fats show similar results, research shows.

According to a 2022 review of clinical trials and observational studies over a five-year period, an “abundance” of observational studies suggest a decreased overall cancer risk from following diets that are more plant-based. When compared to a meat-heavy ketogenic diet, a 2022 review of observational studies found plant-rich diets were more effective at lowering cancer risk, even if keto diets boosted short-term weight loss.

The Bottom Line

Messaging around nutrition and health is both messy and confusing. News stories that announce the results of a single study as fact, without bothering to survey the field, are an ongoing problem that can make dietary choices more complicated than they need to be. Even though some aspects of nutrition science are complex or unknown, there is still a strong consensus on this old gem: eating not too much, mostly plants remains solid advice.