16 Scientific Studies on Vegan Diets That Give Solid Proof On The Health Claims Related To Plant-Based Eating

  1. 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: 18 overweight and obese women with polycystic ovarian syndrome (PCOS) were recruited. Each was randomly assigned to follow a low-fat vegan diet or a low-calorie diet for six months.

Results: Women in the vegan group lost a total of 1.8% of their body weight over the first three months, compared to 0% in the low-calorie group. However, no significant differences were observed after six months.

Interestingly, participants with higher engagement in a Facebook support group lost more weight than the rest.

Those following the vegan diet consumed an average of 265 fewer calories than those on the low-calorie diet, despite not being given a specific lower-calorie goal.

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.

Conclusions: A vegan diet is more effective at naturally reducing the amount of calories eaten per day, despite the lack of a calorie restriction goal. It may also help women with PCOS lose weight.

  1. 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: 50 overweight adults were recruited and randomized to follow one of five low-fat, low-glycemic index diets for six months. The assigned diets were either vegan, vegetarian, pesco-vegetarian, semi-vegetarian or omnivorous.

Participants were given instructions related to their respective diets by a registered dietitian and encouraged 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, omnivores lost only 3.1%.

The vegan diet group consumed more carbs, as well as fewer calories and fat than omnivores, despite not having been given any specific calorie or fat restriction goals.

Protein intakes were not significantly different between groups.

Conclusions: Vegan diets can result in greater weight loss than vegetarian, pesco-vegetarian, semi-vegetarian or omnivorous diets.

Also check out 10 Essential Steps To Improving Your Vegan Diet

  1. Lee, Y-M. et al. Effect 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: 106 type 2 diabetics were randomly assigned to a 12-week vegan or conventional diet recommended by the Korean Diabetes Association (KDA).

Calorie intake was not restricted for either group over the 12-week study period.

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

Hemoglobin A1C 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.

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.

Conclusions: Both diets helped type 2 diabetics’ blood sugar control. However, the vegan diet improved it more than the conventional diet. Also, a vegan diet was more effective at reducing BMI and waist circumference.

  1. 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: 50 type 2 diabetics and 50 healthy subjects were randomly assigned to consume either a protein and saturated fat-rich pork burger or a carb-rich vegan couscous burger.

Blood concentrations of sugar, insulin, triglycerides, free fatty acids, gastric appetite hormones and oxidative stress markers were measured before the meals, as well as up to 180 minutes after the meals.

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

High insulin levels persisted for longer after the meat meal than the vegan meal in both healthy participants and type 2 diabetics.

Triglyceride levels increased and free fatty acids decreased to a higher extent following the meat meal. This happened in both groups, but the difference was more obvious in type 2 diabetics.

The meat meal produced a greater decrease in the hunger hormone ghrelin than the vegan meal. Additionally, the meat meal led to greater increases in markers of cell-damaging oxidative stress than the vegan meal, but only in diabetics.

Oxidative stress-fighting antioxidant activity increased following the vegan meal, but only in healthy controls.

Conclusions: In healthy individuals, vegan meals reduce hunger less but increase antioxidant activity more. Meat meals cause more oxidative stress in diabetics and greater increases in blood sugar levels.

  1. 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: 20 obese men were randomly assigned to consume either a vegetarian or meat-based, high-protein weight loss diet for 14 days.

After the first 14 days, the diets were switched 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 was based on soy protein.

All food was supplied by the dietetic research staff.

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

No differences in hunger ratings or the desire to eat were noted 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 and HDL cholesterol, as well as 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 considered significant.

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

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

Details: 40 participants with osteoarthritis were randomly assigned to consume either a whole-food, plant-based vegan diet or their existing omnivorous diet for six weeks.

Participants in both groups were encouraged to eat freely and not count calories. Both groups prepared their own meals for the duration of the study.

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

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

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

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

Details: 43 participants with rheumatoid arthritis were randomly assigned to consume either a raw, vegan diet rich in lactobacilli or their existing omnivorous diet for one month.

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

Gut flora was measured through stool samples. Disease activity was evaluated through the use of several questionnaires.

Results: The participants consuming the probiotic-rich, raw vegan diet had a significant change in their fecal flora during the study period.

No changes were observed in the fecal flora of the participants on the existing omnivorous diet.

Participants in the probiotic-rich, raw vegan group experienced significantly more improvements in disease symptoms, such as swollen and tender joints.

Conclusions: A probiotic-rich, raw vegan diet changes gut flora and decreases symptoms of rheumatoid arthritis more effectively than a standard omnivorous diet.

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

Details: This study used the same 43 participants with rheumatoid arthritis as in the study above.

Participants were randomly assigned to follow a lactobacilli-rich, raw vegan diet or continue with their existing omnivorous diet for 2–3 months.

Those in the vegan group received pre-packed, probiotic-rich raw meals for the duration of the study.

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 slightly decreased, but only in the raw vegan group.

Participants in the raw 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.

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


Weight Loss

10 of the randomized controlled trials above examined the effects of a vegan diet on weight loss.

Seven out of the 10 studies reported that a vegan diet was more effective than the control diet at helping participants lose weight.

In the most impressive study, the vegan diet was able to help participants lose 9.3 more pounds (4.2 kg) than the control diet over an 18-week period (3).

This effect persisted even when the vegan participants were allowed to eat until fullness, while the control groups had to restrict their calories (69).

This natural tendency to consume fewer calories on a vegan diet could be due to the higher intake of dietary fiber, which is known for inducing satiety (34611).

Also check Why Your Vegan Diet Made You Gain Weight And What To Do Instead

Blood Sugar Levels and Insulin Sensitivity

Despite being generally higher in carbs, vegan diets were up to 2.4 times more effective at improving blood sugar control in diabetics, compared to control diets.

In fact, seven out of eight randomized controlled studies reported vegan diets to be more effective than conventional ones, including diets recommended by the ADA, AHA and NCEP.

The one study that didn’t find the vegan diet to be better reported it to be as effective as the control diet (12).

Part of the advantage of the vegan diet could be explained by the higher fiber intake, which could somewhat blunt the blood sugar response (36411).

The greater weight loss generally reported in participants following the vegan diet could further contribute to the blood sugar-lowering effects.

LDL, HDL and Total Cholesterol

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

Their results indicate that vegan diets are much more effective at reducing total and LDL cholesterol than omnivorous control diets (12313).

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

Appetite and Satiety

Only two of the 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, whereas the second reports no difference between a vegan meal and a meat-containing meal in diabetics (1213).

Symptoms of Arthritis

So far, only three randomized controlled studies looked at the effects of a vegan diet on osteo- or rheumatoid arthritis.

All three report that the vegan diet improved symptoms more effectively than the previous omnivorous diet (141516).

Take Home Message

Vegan diets seem to be very effective at helping people lose weight.

They also seem to be well suited to reduce symptoms of arthritis.

In addition, there’s scientific evidence to support that vegan diets greatly reduce blood sugar, total cholesterol and LDL cholesterol.

Based on the best available evidence, a vegan diet can be very healthy if done right.