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Vegan diets are growing in popularity for health and environmental reasons.

They claim to offer various health benefits, ranging from weight loss and reduced blood sugar to prevention of heart disease, cancer, and premature death.

Randomized controlled studies are a reliable way to collect evidence on the benefits of a diet.

This article analyzes 16 randomized controlled studies to evaluate how a vegan diet can affect your health.

The Studies

1. Wang, F. et al. Effects of Vegetarian Diets on Blood Lipids: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.Journal of the American Heart Association, 2015.

Details: This meta-analysis included 832 participants. It looked at 11 studies of vegetarian diets, seven of which were vegan. Each of the studies on vegan diets had a control group. The studies lasted from 3 weeks to 18 months.

The researchers evaluated changes in:

• total cholesterol
• low-density lipoprotein (LDL) “bad” cholesterol
• high-density lipoprotein (HDL) “good” cholesterol
• non-HDL cholesterol
• triglyceride levels

Results: Vegetarian diets lowered all cholesterol levels more than the control diets, but they didn’t affect blood triglyceride levels. The findings didn’t refer specifically to vegan diets.

Vegetarian diets effectively lowered blood levels of total, LDL (bad), HDL (good), and non-HDL cholesterol more than the control diets. It’s unclear whether a vegan diet has a similar impact.

2. Macknin, M. et al. Plant-Based, No Added Fat or American Heart Association Diets: Impact on Cardiovascular Risk in Obese Children with Hypercholesterolemia and Their Parents.The Journal of Pediatrics, 2015.

Details: This study involved 30 children with obesity and high cholesterol levels and their parents. Each pair followed either a vegan diet or an American Heart Association (AHA) diet for 4 weeks.

Both groups attended weekly classes and cooking lessons specific to their diet.

Results: Total calorie intake fell significantly in both diet groups.

Children and parents who followed the vegan diet consumed less protein, cholesterol, saturated fat, vitamin D, and vitamin B12. They also consumed more carbs and fiber than those in the AHA group.

Children following the vegan diet lost 6.7 pounds (3.1 kg), on average, during the study period. This was 197% more than the weight lost by those in the AHA group.

At the end of the study, children following the vegan diet had a significantly lower body mass index (BMI) than those following the AHA diet.

Parents in the vegan groups had an average of 0.16% lower HbA1c level, a measure of blood sugar management. They also had lower total and LDL (bad) cholesterol levels than those on the AHA diet.

Both diets lowered heart disease risk in children and adults. However, the vegan diet had a greater impact on the children’s weight and the parents’ cholesterol and blood sugar levels.

3. Mishra, S. et al. A multicenter randomized controlled trial of a plant-based nutrition program to reduce body weight and cardiovascular risk in the corporate setting: The GEICO study.European Journal of Clinical Nutrition, 2013.

Details: Researchers recruited 291 participants from 10 GEICO corporate offices. Each office was paired with another, and employees from each paired site followed either a low fat vegan diet or a control diet for 18 weeks.

Participants in the vegan group received weekly support group classes led by a dietitian. They took a daily vitamin B12 supplement and were encouraged to favor low glycemic index foods.

Participants in the control group made no dietary changes and didn’t attend weekly support group sessions.

Results: The vegan group consumed more fiber and less total fat, saturated fat, and cholesterol than the control group.

Participants who followed the vegan diet for 18 weeks lost an average of 9.5 pounds (4.3 kg), compared with 0.2 pounds (0.1 kg) in the control group.

Total and LDL (bad) cholesterol levels dropped by 8 mg/dL in the vegan group, compared to almost no change in the control groups.

HDL (good) cholesterol and triglyceride levels both increased more in the vegan groups than in the control group.

HbA1c levels dropped by 0.7% in the vegan group, compared to 0.1% in the control group.

Participants in the vegan groups lost more weight. They also improved their blood cholesterol and blood sugar levels compared to those following a control diet.

4. Barnard, N. D. et al. The effects of a low-fat, plant-based dietary intervention on body weight, metabolism, and insulin sensitivity.The American Journal of Medicine, 2005.

Details: This study involved 64 females who had overweight and had not yet reached menopause. They followed either a low fat vegan or a low fat control diet based on the National Cholesterol Education Program (NCEP) guidelines for 14 weeks.

There were no calorie restrictions, and both groups were encouraged to eat until they were full. Participants prepared their own meals and attended weekly nutritional support session throughout the study.

Results: Although there was no calorie restriction, both groups consumed around 350 fewer calories per day. The vegan group consumed less dietary protein, fat, and cholesterol and more fiber than the NCEP diet group.

Participants in the vegan group lost an average of 12.8 pounds (5.8 kg), compared to 8.4 pounds (3.8 kg) in those following the NCEP diet. Changes in BMI and waist circumference were also greater in the vegan groups.

Blood sugar levels, fasting insulin, and insulin sensitivity improved significantly for all.

Both diets improved markers of blood sugar management. However, the low fat vegan diet helped participants lose more weight than the low fat NCEP diet.

5. Turner-McGrievy, G. M. et al. A Two-Year Randomized Weight Loss Trial Comparing a Vegan Diet to a More Moderate Low-Fat Diet.Obesity, 2007.

Details: Having completed the above study, the researchers continued to assess 62 of the same participants for 2 years. In this phase, 34 participants had follow-up support for 1 year, but the others received no support.

There were no calorie restriction goals, and both groups continued to eat until they were full.

Results: Those in the vegan group lost an average of 10.8 pounds (4.9 kg) after 1 year, compared to 4 pounds (1.8 kg) in the NCEP group.

Over the next year, both groups regained some weight. After 2 years, the weight loss was 6.8 pounds (3.1 kg) in the vegan group and 1.8 pounds (0.8 kg) in the NCEP group.

Regardless of the diet assignment, the women who received group support sessions lost more weight than those who didn’t receive them.

Females on a low fat vegan diet lost more weight after 1 and 2 years, compared to those following another low fat diet. Also, those who received group support lost more weight and regained less.

6. Barnard, N.D. et al. A Low-Fat Vegan Diet Improves Glycemic Control and Cardiovascular Risk Factors in a Randomized Clinical Trial in Individuals With Type 2 Diabetes.Diabetes Care, 2006.

Details: Researchers recruited 99 participants with type 2 diabetes and pair-matched them based on their HbA1c levels.

The scientists then randomly assigned each pair to follow either a low fat vegan diet or a diet based on the 2003 American Diabetes Association (ADA) guidelines for 22 weeks.

There were no restrictions on portion sizes, calorie intake, and carbs on the vegan diet. Those on the ADA diet were asked to reduce their calorie intake by 500–1,000 calories per day.

Everyone received a vitamin B12 supplement. Alcohol was limited to one serving per day for women and two servings per day for men.

All participants also had an initial one-on-one session with a registered dietitian and attended weekly nutrition group meetings throughout the study.

Results: Both groups consumed approximately 400 fewer calories per day, although only the ADA group had instructions to do so.

All participants reduced their intake of protein and fat, but those in the vegan group consumed 152% more carbs than the ADA group.

Participants following the vegan diet doubled their fiber intake, whereas the amount of fiber consumed by those in the ADA group remained the same.

After 22 weeks, the vegan group lost an average of 12.8 pounds (5.8 kg). This was 134% more weight than the average weight lost in the ADA group.

Total cholesterol, LDL (bad), and HDL (good) cholesterol levels all fell in both groups.

However, in the vegan group, HbA1c levels fell by 0.96 points. This was 71% more than the ADA participants’ levels.

The graph below shows the HbA1c changes in the vegan diet groups (blue) and ADA diet groups (red).

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Both diets helped participants lose weight and improve their blood sugar and cholesterol levels. However, those on the vegan diet experienced greater reductions in weight loss and blood sugar than those following the ADA diet.

7. Barnard, N.D. et al. A low-fat vegan diet and a conventional diabetes diet in the treatment of type 2 diabetes: a randomized, controlled, 74-wk clinical trial.American Journal of Clinical Nutrition, 2009.

Details: Researchers followed participants from the previous study for an additional 52 weeks.

Results: By the end of the 74-week study period, the 17 participants in the vegan group had reduced their diabetes medication dosages, compared with 10 people in the ADA group. HbA1c levels fell to a greater extent in the vegan group.

Participants in the vegan group also lost 3 pounds (1.4 kg) more weight than those on the ADA diet, but the difference wasn’t statistically significant.

In addition, LDL (bad) and total cholesterol levels fell by 10.1–13.6 mg/dL more in the vegan groups than in the ADA group.

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Both diets improved blood sugar and cholesterol levels in people with type 2 diabetes, but the impact was greater with the vegan diet. Both diets contributed to weight loss. The differences between the diets weren’t significant.

8. Nicholson, A. S. et al. Toward Improved Management of NIDDM: A Randomized, Controlled, Pilot Intervention Using a Low-Fat, Vegetarian Diet.Preventive Medicine, 1999.

Details: Eleven people with type 2 diabetes followed either a low fat vegan diet or a conventional low fat diet for 12 weeks.

All participants were offered prepared lunches and dinners according to their diet specifications. Participants could also opt to prepare their own meals if they preferred, but most used the catered meal option.

The vegan diet contained less fat, and participants consumed around 150 fewer calories per meal than those on the conventional diet.

All participants attended an initial half-day orientation session, as well as support group sessions every other week throughout the study.

Results: In the vegan group, fasting blood sugar levels fell by 28%, compared with a 12% decrease in those following the conventional low fat diet.

People on the vegan diet also lost an average of 15.8 pounds (7.2 kg) over 12 weeks. Those on the conventional diet lost an average of 8.4 pounds (3.8 kg).

There were no differences in total and LDL (bad) cholesterol levels, but HDL (good) cholesterol levels fell in the vegan group.

A low fat vegan diet may help reduce fasting blood sugar levels and help people lose more weight than a conventional low fat diet.

9. Turner-McGrievy, G. M. et al. Low glycemic index vegan or low-calorie weight loss diets for women with polycystic ovary syndrome: a randomized controlled feasibility study.Nutrition Research, 2014.

Details: Eighteen females with overweight or obesity and polycystic ovarian syndrome (PCOS) followed either a low fat vegan diet or a low calorie diet for 6 months. There was also an option to join a Facebook support group.

Results: Those in the vegan group lost a total of 1.8% of their body weight over the first 3 months, while those in the low-calorie group didn’t lose weight. However, there were no significant differences after 6 months.

In addition, participants with a higher engagement in a Facebook support group lost more weight than those who didn’t engage.

People who followed the vegan diet consumed an average of 265 fewer calories than those on the low-calorie diet, despite having no calorie restriction.

Participants in the vegan group also consumed less protein, less fat, and more carbs than those following the low calorie diet.

No differences were observed in pregnancy or PCOS-related symptoms between the two groups.

A vegan diet may help reduce calorie intake, even without a calorie restriction goal. It may also help females with PCOS lose weight.

10. Turner-McGrievy, G. M. et al. Comparative effectiveness of plant-based diets for weight loss: A randomized controlled trial of five different diets.Nutrition, 2015.

Details: Fifty adults with overweight followed one of five low fat, low glycemic index diets for 6 months. The diets were either vegan, vegetarian, pesco-vegetarian, semi-vegetarian, or omnivorous.

A registered dietitian advised participants about their diet and encouraged them to limit processed and fast food.

All participants, except those in the omnivorous diet group, attended weekly group meetings. The omnivore group attended monthly sessions and received the same diet information through weekly emails instead.

All participants consumed a daily vitamin B12 supplement and had access to private Facebook support groups.

Results: Participants in the vegan group lost an average of 7.5% of their body weight, which was the most of all groups. In comparison, those in the omnivore group lost only 3.1%.

Compared with the omnivore group, the vegan group consumed more carbs, fewer calories, and less fat, despite not having any calorie or fat restriction goals.

Protein intakes were not significantly different between groups.

Vegan diets may be more effective for losing weight than a vegetarian, pesco-vegetarian, semi-vegetarian, or omnivorous diet.

11. Lee, Y-M. et al. Effects of a Brown Rice Based Vegan Diet and Conventional Diabetic Diet on Glycemic Control of Patients with Type 2 Diabetes: A 12-Week Randomized Clinical Trial.PLoS ONE, 2016.

Details: In this study, 106 people with type 2 diabetes followed either a vegan diet or a conventional diet recommended by the Korean Diabetes Association (KDA) for 12 weeks.

There was no restriction on calorie intake for either group.

Results: Participants in the vegan group consumed an average of 60 fewer calories per day, compared with the conventional diet group.

HbA1c levels decreased in both groups. However, those in the vegan group reduced their levels by 0.3–0.6% more than the conventional diet group.

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Interestingly, BMI and waist circumference decreased only in the vegan group.

There were no significant changes in blood pressure or blood cholesterol levels between groups.

Both diets helped with blood sugar management, but the vegan diet had more impact than the conventional diet. A vegan diet was also more effective at reducing BMI and waist circumference.

12. Belinova, L. et al. Differential Acute Postprandial Effects of Processed Meat and Isocaloric Vegan Meals on the Gastrointestinal Hormone Response in Subjects Suffering from Type 2 Diabetes and Healthy Controls: A Randomized Crossover Study.PLoS ONE, 2014.

Details: Fifty people with type 2 diabetes and 50 without diabetes consumed either a protein and saturated fat-rich pork burger or a carb-rich vegan couscous burger.

Researchers measured blood concentrations of sugar, insulin, triglycerides, free fatty acids, gastric appetite hormones, and oxidative stress markers before the meal and up to 180 minutes after the meal.

Results: Both meals produced similar blood sugar responses in both groups over the 180-minute study period.

Insulin levels stayed high for longer after the meat meal than the vegan meal, regardless of diabetes status.

Triglyceride levels rose, and free fatty acids fell more after the meat meal. This happened in both groups, but the difference was greater in those with diabetes.

The meat meal produced a greater decrease in the hunger hormone ghrelin than the vegan meal, but only in healthy participants. In those with diabetes, ghrelin levels were similar after both types of meals.

In those with diabetes, markers of cell-damaging oxidative stress rose more after the meat meal than after the vegan meal.

Those without diabetes experienced an increase in antioxidant activity after the vegan meal.

In healthy individuals, vegan meals may be less effective at reducing hunger less but better at increasing antioxidant activity. Meat meals are more likely to trigger more oxidative stress in people with diabetes. This may lead to a greater need for insulin.

13. Neacsu, M. et al. Appetite control and biomarkers of satiety with vegetarian (soy) and meat-based high-protein diets for weight loss in obese men: A randomized crossover trial.The American Journal of Clinical Nutrition, 2014.

Details: Twenty men with obesity followed either a vegetarian or meat-based, high-protein weight loss diet for 14 days.

After the first 14 days, the participants switched diets, so that the vegetarian group received the meat-based diet for the following 14 days and vice versa.

Diets were calorie-matched and provided 30% of calories from protein, 30% from fat, and 40% from carbs. The vegetarian diet provided soy protein.

The dietetic research staff provided all the food.

Results: Both groups lost around 4.4 pounds (2 kg) and 1% of their body weight, regardless of the diet they consumed.

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There was no difference in hunger ratings or the desire to eat between the groups.

The pleasantness of the diets was rated high for all meals, but participants generally rated the meat-containing meals higher than the soy-based vegan ones.

Both diets reduced total, LDL (bad) and HDL (good) cholesterol, triglycerides, and glucose. However, the decrease in total cholesterol was significantly greater for the soy-based vegan diet.

Levels of ghrelin were slightly lower in the meat-based diet, but the difference wasn’t large enough to be significant.

Both diets had similar effects on weight loss, appetite and gut hormone levels.

14. Clinton, C. M. et al. Whole-Foods, Plant-Based Diet Alleviates the Symptoms of Osteoarthritis.Arthritis, 2015.

Details: Forty people with osteoarthritis followed either a whole-food, plant-based vegan diet or their regular omnivorous diet for 6 weeks.

All participants received instructions to eat freely and not count calories. Both groups prepared their own meals during the study.

Results: Participants in the vegan group reported greater improvements in energy levels, vitality, and physical functioning, compared with the regular diet group.

The vegan diet also resulted in higher scores on self-rated functioning assessments among participants with osteoarthritis.

A whole-food, plant-based vegan diet improved symptoms in participants with osteoarthritis.

15. Peltonen, R. et al. Faecal microbial flora and disease activity in rheumatoid arthritis during a vegan diet.British Journal of Rheumatology, 1997.

Details: This study involved 43 people with rheumatoid arthritis. Participants consumed either a raw, vegan diet rich in lactobacilli or their habitual omnivorous diet for 1 month.

The participants in the vegan group received pre-packed, probiotic-rich raw meals throughout the study.

Researchers used stool samples to measure gut flora and questionnaires to evaluate disease activity.

Results: Researchers found significant changes in the fecal flora of participants who consumed the probiotic-rich, raw vegan diet, but no changes in those who followed their usual diet.

Participants in the vegan group also experienced significantly more improvements in disease symptoms, such as swollen and tender joints.

A probiotic-rich, raw vegan diet appears to change gut flora and decrease symptoms of rheumatoid arthritis, compared with a standard omnivorous diet.

16. Nenonen, M.T. et al. Uncooked, lactobacilli-rich, vegan food and rheumatoid arthritis.British Journal of Rheumatology, 1998.

Details: This study followed the same 43 participants as the study above, but for an additional 2–3 months.

Results: The participants in the raw vegan group lost 9% of their body weight, while the control group gained 1% of their body weight, on average.

By the end of the study, blood protein and vitamin B12 levels fell slightly, but only in the vegan group.

Participants in the vegan group reported significantly less pain, joint swelling, and morning stiffness than those continuing with their existing diet. A return to their omnivorous diet aggravated their symptoms.

However, when scientists used more objective indicators to measure rheumatoid arthritis symptoms, they didn’t find any difference between the groups.

Some of the participants on the vegan diet reported symptoms of nausea and diarrhea, which caused them to withdraw from the study.

A probiotic-rich, raw vegan diet increased weight loss and improved subjective disease symptoms in those with rheumatoid arthritis.

Weight loss

Ten of the above studies looked at the effects of a vegan diet on weight loss. In 7 of those 10 studies, a vegan diet appeared to be more effective than the control diet at helping participants lose weight.

In one study, participants on the vegan diet lost 9.3 more pounds (4.2 kg) in 18 weeks than those following the control diet (3).

This was true even when the vegan participants were allowed to eat until fullness, while the control groups had to restrict their calories (6, 9).

The tendency to consume fewer calories on a vegan diet could be due to the higher intake of dietary fiber, which can help people feel full (3, 4, 5, 10).

The lower fat content of most of the vegan diets used in these studies may also have contributed (2, 3, 4, 8, 9).

However, when the diets were matched for calories, the vegan diet was no more effective than the control diet for weight loss (12).

Not many studies explained whether the weight loss came from the loss of body fat or the loss of body muscle.

Blood sugar levels and insulin sensitivity

While generally higher in carbs, the vegan diets were up to 2.4 times more effective at improving blood sugar management in people with diabetes, compared to control diets.

In 7 out of 8 studies, research showed that a vegan diet improved glucose management more effectively than a conventional diet, including those recommended by the ADA, AHA, and NCEP.

In the eighth study, researchers reported that the vegan diet was as effective as the control diet (11).

This may be due to the higher fiber intake, which could blunt the blood sugar response (3, 5, 4, 10).

The greater weight loss on the vegan diet may also help lower blood sugar levels.

LDL, HDL, and total cholesterol

In total, 14 studies examined the impact of vegan diets on blood cholesterol levels.

Vegan diets appear to be more effective at reducing total and LDL (bad) cholesterol, compared with the omnivorous control diets (1, 2, 3,12).

However, the effects on HDL (good) cholesterol and triglyceride levels are mixed. Some studies reported increases, others decreases, and some no effect at all.

Appetite and satiety

Only two studies looked at the effects of vegan diets on appetite and satiety.

The first reported that a vegan meal reduced the hunger hormone ghrelin less than a meat-containing meal in healthy participants. The second reported no difference between a vegan meal and a meat-containing meal in people with diabetes (11, 12).

Symptoms of arthritis

Three of the studies looked at how a vegan diet might affect osteoarthritis or rheumatoid arthritis.

In all three studies, participants said the vegan diet improved their symptoms more effectively than their usual omnivorous diet (13, 14, 15).

The bottom line

A vegan diet may contribute to weight loss and help people manage their blood sugar and cholesterol levels.

It may also help reduce the symptoms of arthritis.

A well-planned vegan diet may offer a range of health benefits.