A fresh study on vegan and meat-based eating is getting attention for an unusual reason. Instead of giving either side a clean win, it handed both camps something to cheer and something to criticize.
The research, published in late November 2023, followed identical twins and found that people assigned to a healthy vegan diet saw bigger short-term improvements in several heart health measures than twins assigned to a healthy omnivorous diet. But the trial was small, lasted just eight weeks, and compared carefully planned diets rather than the way most Americans actually eat.
What the new study found
The study was published November 30, 2023, in JAMA Network Open by researchers at Stanford Medicine. It enrolled 22 pairs of identical twins, or 44 adults total, and randomly assigned one twin in each pair to a vegan diet and the other to an omnivorous diet for eight weeks. Because identical twins share the same genes and much of the same early-life environment, researchers said the design helped control for factors that often muddy nutrition studies.
During the first four weeks, participants were given 21 meals per week prepared for them. For the final four weeks, they prepared their own meals while receiving nutrition support. Both diets were designed to be healthy, with an emphasis on vegetables, legumes, fruits, and whole grains, according to the study team.
By the end of the trial, the vegan group showed lower LDL cholesterol, lower fasting insulin, and greater weight loss than the omnivorous group. The paper reported an average LDL drop of about 13 mg/dL in the vegan group, compared with little change in the omnivorous group. The vegan group also lost roughly 4.2 pounds on average, compared with about 1.5 pounds in the omnivorous group.
Researchers also reported a reduction in trimethylamine N-oxide, or TMAO, a compound linked in some studies to cardiovascular risk. “Our study used a twin design to control for genetics, lifestyle and upbringing, and these factors can confound nutrition studies,” lead author Dr. Christopher Gardner of Stanford said in a statement released with the paper.
Why vegans are not celebrating outright
On paper, the headline result looks like a clear point for plant-based eating. But some vegan advocates were frustrated that the study stopped short of claiming vegan diets are universally superior, and that is partly because the researchers were careful about what they actually tested. This was not vegan eating in the broad sense. It was a short, structured, health-focused version of it.
The vegan diet in the study was lower in calories on average, especially early in the trial, and participants also consumed less saturated fat and more fiber. Critics on the vegan side argue that the improvements may reflect those shifts more than the simple absence of animal foods. In other words, the study supports a well-planned vegan diet, but not every vegan diet.
Some also noted that nutrients including vitamin B12 must be monitored on vegan diets over time, a point the study did not really address because the intervention lasted only eight weeks. Long-term outcomes like bone health, muscle maintenance in older adults, and diet adherence over years were outside the scope of the trial.
Even supporters of plant-based eating said the public conversation around the study quickly became too simplistic. A short trial with prepared meals and dietitian guidance is very different from real-life grocery budgets, family eating habits, and the convenience-driven food choices many Americans make each week.
Why meat eaters are pushing back too
People who favor meat-inclusive diets found plenty to object to as well. One big complaint is that the omnivorous diet was not a test of a higher-protein, lower-carb pattern that many meat eaters say works well for weight control and blood sugar. Instead, the omnivorous plan was also built around healthy staples and included animal products in moderate amounts.
That matters because the study did not compare vegan eating against a typical American diet heavy in burgers, fries, soda, and ultra-processed snacks. Nor did it compare vegan eating against a rigorously designed Mediterranean diet, a paleo-style plan, or a high-protein athletic diet. It compared two health-conscious diets under close supervision.
Some critics also pointed out that calorie intake differed between the groups, especially at the start. If one group eats fewer calories and less saturated fat, many dietitians would expect weight and LDL cholesterol to improve regardless of ideology. That does not invalidate the findings, but it does make sweeping claims harder to defend.
Others raised the issue of protein quality and muscle preservation, especially for older adults or highly active people. The study did not report dramatic harms in the vegan group, but it was not long enough to answer questions about body composition, strength, or whether participants could maintain the same eating pattern over many months.
What experts say the study really means
Outside experts broadly described the trial as useful but limited. The twin design won praise because it is rare in nutrition research and helps reduce some common confounding problems. At the same time, specialists noted that 44 participants is still a small sample, and eight weeks is a very short window for a debate that often centers on lifelong health.
Many nutrition researchers say the most defensible takeaway is fairly modest. If people replace foods high in saturated fat with legumes, whole grains, vegetables, fruits, nuts, and other fiber-rich plant foods, markers tied to heart disease risk often improve. That conclusion lines up with years of evidence supporting dietary patterns rich in minimally processed plants.
The flip side is just as important. The study does not show that all meat is harmful or that everyone should stop eating animal products. Lean meats, fish, eggs, yogurt, and other animal foods can fit into healthy eating patterns, including Mediterranean-style diets that have also been linked to heart benefits in large bodies of research.
Dr. Gardner himself has often framed food choices less as a purity test and more as a quality question. For many experts, the bigger issue is not vegan versus meat in an abstract culture-war sense. It is whether a person is eating mostly whole foods or mostly ultra-processed products, and whether the diet is sustainable in daily life.
Why this matters for Americans right now
The study landed at a time when Americans are getting hit with two competing messages. One says meat is the problem. The other says plants are not enough. For a public dealing with high grocery prices, rising rates of obesity and diabetes, and a flood of diet advice online, neither message is especially helpful on its own.
Heart disease remains the leading cause of death in the United States, according to federal health data, so any study that shows even short-term improvements in LDL cholesterol and insulin will get attention. But real-world eating is shaped by cost, culture, access, cooking time, and personal preference. Prepared meals and dietitian coaching are not standard conditions in most households.
That is one reason both sides ended up annoyed. The study offered evidence that a healthy vegan diet can improve several cardiometabolic markers quickly, but it did not prove that vegan eating is the only healthy path. It also suggested that some advantages may come from eating fewer calories and less saturated fat, not from ideology.
For most readers, the practical lesson is less dramatic than the internet reaction. Eating more beans, vegetables, fruit, and whole grains, while cutting back on saturated fat and heavily processed foods, is still one of the safest bets in nutrition. Whether some meat stays on the plate is, at least based on this study, not the whole story.
