Is Eating a Plant-Based Diet Better for You?

Here's what the research says.

It’s no secret that fruits and veggies are good for you. But a new Netflix show, You Are What You Eat: A Twin Experiment, shows just how powerful—and fast-acting—they can be.

The show features pairs of adult identical twins who participated in a study published in November 2023. For eight weeks, everyone in the study ate a diet rich in fruits, vegetables, whole grains, and legumes and low in sugars and refined starches. But one twin from each pair was assigned to eat only these plant-based foods, while the other also ate animal products such as chicken, fish, eggs, and dairy.

Both groups saw improvements in their cholesterol levels and modest reductions in weight over the eight weeks, but those trends were more dramatic among twins who followed the vegan diet. Average fasting insulin levels—another marker of cardiometabolic health—also dropped among the vegan, but not omnivorous, twins.

“This suggests that anyone who chooses a vegan diet can improve their long-term health in two months,” Christopher Gardner, a Stanford University professor and senior author of the study, said in a statement. And, Gardner added, following a vegan diet may not be as difficult as many people imagine: 21 of the 22 twins assigned to that eating plan stuck with it for all eight weeks.

Another point for plants

The Stanford study is not the only recent evidence pointing to the promise of plant-rich diets. A study published December 2023 in JAMA Network Open found that people who eat low-carbohydrate diets rich in plant-based proteins and fats, as well as whole grains, tend to gain less weight over time than people who eat low-carb diets with a lot of animal products and refined starches.

“Having a diet that’s rich in fresh fruits, non-starchy vegetables, whole grains, nuts, legumes, and plant-based oils is advisable for maintaining or improving your overall health,” says Binkai Liu, a research assistant in the Harvard T.H. Chan School of Public Health’s nutrition department and first author of the JAMA Network Open study.

Two recent analyses of previously published studies also found benefits associated with plant-based diets. The first linked vegetarian diets to a lower risk of heart disease than omnivorous diets, while the second, like the twin study, found that vegan and vegetarian diets are associated with lower levels of cholesterol and other markers of potential heart problems.

Which is more important: more plants or less meat?

In addition to validating plant-based diets, studies have long shown that eating too much meat—particularly red and processed meat, such as sausage and bacon—is linked to health problems including heart disease and cancer. But is all meat consumption bad?

It’s debatable. Some studies and experts refute the idea that vegan diets are automatically healthier than those that include meat. Becoming a vegan or vegetarian can make it difficult to get certain nutrients found in animal products, such as vitamins B12 and D, and people who eliminate meat often replace it with foods that may limit the nutritional benefits of a vegetarian lifestyle. Plus, numerous studies suggest that people who eat a Mediterranean diet—which includes fish—tend to live longer and report better health than people who follow other eating styles.

In the statement, Gardner said that cutting out all meat shouldn’t necessarily be everyone’s goal. “What’s more important than going strictly vegan,” Gardner said, “is including more plant-based foods into your diet.” Even the omnivores in his study, after all, saw some drops in cholesterol and body weight after eight weeks, likely in part because they ate plenty of fresh foods high in fiber and low in saturated fat.

A study from 2017 backs up that idea. Researchers tracked a group of people for more than a decade to see how dietary changes affected longevity. They estimated that even one small daily change—swapping a serving of red or processed meat for nuts or legumes—translated to an 8% to 17% drop in early death risk.

It’s hard to make one-size-fits-all statements when it comes to nutrition, as people’s bodies are unique and have different needs. Another twin study, this one from 2019, found that even people share nearly all of their DNA can have different physiological responses to the same foods, for example.

But if there’s any universal truth in nutrition science, it seems to be that loading up your plate with plants is always a good decision.