Table 1.

Intervention studies on the effect of plant-based diets

Author Year	Study design	n patients	n healthy	Nature of intervention, and if calorie-restricted	Duration of intervention	Measures	Effect of intervention	Favoring vegan diet
Weight loss, blood-based metabolic markers
Turner-McGrievy et al. (2007)139	RCT; overweight postmenopausal women: low-fat vegan vs. National Cholesterol Education Program diet two replications		62; first run 28 (14 vs. 14), second run 34 (17 vs. 17)	Low-fat vegan diet (unrestricted): − fruits, vegetables, legumes, grains − animal products proscribed − limit high-fat plant foods vs. National Cholesterol Education Program diet (unrestricted): − see guidelines	14 weeks (24 months follow-up)	Body weight	− weight loss higher in vegan group at year 1 and year 2	+
Burke et al. (2008)140	RCT; obese subjects; four groups: freely chosen vegetarian vs. freely chosen conventional vs. assigned vegetarian vs. assigned conventional		178 (48 vs. 35 vs. 48 vs. 45)	Vegetarian (restricted): − no meat, poultry, fish vs. Standard behavioral therapy, group sessions led by dietician/physiologist/nurse/behavioral scientist − monitoring of physical activity and calorie/fat content of foods − cooking magazines provided	18 months	Body weight	− weight loss higher in both groups that were assigned to a certain diet − trend to higher weight loss in both vegetarian groups − all groups showed significant weight loss	+
Barnard et al. (2009)141	RCT; T2DM patients; two groups: Vegan vs. conventional restrictive diet	99 (49 vs. 50)		Vegan (unrestricted): − 10% fat, 15% protein, 75% carbohydrates − daily cholesterol intake < 50 mg − vegetables, fruit, grains, legumes − no animal products, fatty foods and high-glycaemic index foods vs. Conventional: −<7% fat, 15−20% protein, 60−70% carbohydrates − meal plan with dietician, 3-day dietary record	74 weeks	Body weight, blood measures	− significant weight loss in both groups (trend towards stronger effect in vegan group) − lower HbA1C, total-/LDL-/ and non-HDL-cholesterol after intervention in both groups, trend towards lower HbA1C in vegan group − controlling for medication changes led to significantly greater reductions in HbA1C, total- and LDL-cholesterol in vegan group	+
Elkan et al. (2008)40	Rheumatoid arthritis patients	66 (38 vs. 28)		Gluten-free vegan diet (protein energy level was 10% of the total energy intake, the carbohydrates 60%, and fat 30%; contained vegetables, root vegetables, nuts, fruits) vs. well-balanced non-vegan (contained 10 to 15% protein, 55 to 60% carbohydrate, no more than 30% fat)	12 months	Body weight, blood measures	− lower BMI, LDL, TC and higher anti-PC IgM in the vegan diet group	+
Marniemi et al. (1990)142	Moderately obese subjects		110 in total (31 vs. 37 vs. 42)	Lactoovo (1200 kcal/day) vs. mixed diet (1200 kcal/day) vs. control (no intervention)	12 months	Body weight, blood measures	− Weight-reduction, improved lipid metabolism in both intervention groups, stronger effects in mixed diet compared to lactovegetarian diet	−
Acharya et al. (2013)143	Pilot study for RCT; overweight and obese subject		143 in total (79 vs. 64)	Standard calorie- and fat-restricted diet vs. calorie- and fat-restricted lacto-ovo-vegetarian diet	6 months	Body weight	− no significant effect on weight dependent on diet	o
Wright et al. (2017)144	RCT; mid-age to old T2DM and overweight patients; whole food plant-based unrestricted vs. usual care	65 (32 vs. 33)		Low-fat plant-based: − 7−15% fat − whole grains, legumes, vegetables, fruits − calorie-unrestricted − avoid animal products and refined oils, high-fat plant foods, sugar, salt, caffeine − 50 μg/day vitamin B12	6 months	Body weight, blood measures	− reduced BMI and mean cholesterol in plant-based group	+
Jenkins et al. (2014)29	RCT; overweight hyperlipidemic patients; low-carb vegan vs. high-carb lacto-ovo	39 (19 vs. 20)		− caloric restriction to 60% of estimated caloric requirements low-carb vegan: − 26% carbohydrates, 31% plant protein, 43% fat vs. high-carb lacto-ovo-vegetarian: − 58% carbohydrates, 16% protein, 25% fat	6 months	Body weight, blood measures	− higher weight loss and lower LDL and TG for low-carb vegan group after 1 month31: − weight loss reduced in both groups (about 4.0 kg) (n.s. difference across groups) − more reduced LDL, TC, apolipoproteins for plant-based group	+
Turner-McGrievy et al. (2015)33,161	RCT; healthy overweight subjects 25-49.9 kg/m2; calorie-unrestricted		50 (12 vs. 13 vs. 13 vs. 12)	− avoid fast foods and processed foods; self-based diets − all groups received weekly dietary sessions except for the omnivore group (kept following their usual diet) vegan: − no animal products, focus on plant-based foods vs. vegetarian: − no meat, fish, poultry, but eggs and dairy vs. pesco-vegetarian: − no meat, poultry, but fish, shellfish, eggs, dairy vs. semi-vegetarian: − all foods, red meat limited to 1/week and poultry limited to <5/week	6 months	Body weight, blood measures	− higher weight loss in vegan group (particularly decreased fat and saturated fat)	+
Turner-McGrievy et al. (2014)145	RCT; overweight subjects with polycystic syndrome: vegan vs. low-calorie diet	18 (9 vs. 9)		Vegan: − exclude all animal products, limit high glycaemic-index foods vs. Low-calorie: − restricted to 1200−1500 kcal/day depending on body weight − assessed by weekly 24 h recall	6 months	Body weight, polycystic syndrome	− higher weight loss at 3 months for vegan group (not after 6 months) − lower energy intake after 6 months for vegan group (lower fat, lower protein) − no changes for polycystic syndrome	+/o
Kahleova et al. (2011)146	RCT; T2DM patients; two groups: vegetarian vs. conventional diabetic diet	74 (37 vs. 37)		Vegetarian (restricted) vs. Conventional (restricted) − all meals provided − after 12 weeks physical exercise added	6 months	Body weight, polycystic syndrome	− reduced medication, higher weight loss, increased insulin sensitivity, reduced visceral and subcutaneous fat, increase in plasma adiponectin, decrease in leptin in the vegan group	+
Ferdowsian et al. (2010)147	RCT; overweight and/or T2DM patients: low-fat vegan diet vs. control; onsite	113		Low-fat vegan: − no meat, poultry, fish, dairy, eggs, <5% saturated fat, <25% total fat, < 50 mg cholesterol daily − multivitamin supplement (incl. B12) vs. control: − usual diet	5,5 months	Body weight	− reduced body weight and waist circumference in intervention group	+
Mishra et al. (2013) (same sample as Agarwal et al. (2015) and partly overlapping with Ferdowsian et al. (2010))147–149	RCT; overweight and/or T2DM patients; multicomponent worksite intervention; low-fat vegan vs. usual diet	291 at 4 sites; (142 vs. 149)		low-fat vegan (unrestricted): − avoid all animal products, minimize added oils, favor whole grains − vitamin B12 and multivitamin supplements vs. Control: − usual diet; no instruction	18 weeks	Blood measures	− lower total cholesterol in vegan group	+
Kahleova et al. (2018)150	RCT; T2DM patients	74 (37 vs. 37)		vegetarian diet (−500 kcal/day) vs. control isocaloric conventional anti-diabetic diet (−500 kcal/day)	16 weeks	Anthropo-metric measures	− greater reduction in total leg area for thigh adipose tissue distribution after vegetarian diet	+
Lee et al. (2016)28	RCT; healthy Korean subjects; two groups: Vegan vs. conventional restrictive diet		106 (46 vs. 47)	Vegan (unrestricted): (1) ingest unpolished rice (brown rice); (2) avoid polished rice (white rice); (3) avoid processed food made of rice flour or wheat flour; (4) avoid all animal food products (i.e., meat, poultry, fish, daily goods, and eggs); and (5) favor low-glycemic index foods (e.g., legumes, legumes-based foods, green vegetables, and seaweed) vs. Conventional (restricted) (1) restrict their individualized daily energy intake based on body weight, physical activity, need for weight control, and compliance; (2) total calorie intake comprised 50–60% carbohydrate, 15–20% protein (if renal function is normal), <25% fat, <7% saturated fat, minimal trans-fat intake, and ≤200 mg/day cholesterol	12 weeks	Body weight, blood measures	− significantly larger reduction of HbA1C levels, trends towards lower BMI and lower waist circumference in the vegan intervention group	+
Barnard et al. (2000)151	RCT; premenopausal women	51 (35)		low-fat vegetarian (10% fat) vs. normal diet incl. a placebo pill	3 months	Blood measures	− decreased LDL, HDL, TC after 10% fat-vegetarian diet	+
Rauma et al.39	Rheumatoid arthritis patients	43 (22 vs. 21)		vegan vs. control (usual diet)	3 months	Body weight, urine measures	− 9% reduction of body weight in the vegan group	+
Gardner et al. (2005)152	RCT; hypercholesterolemic outpatients 30−65 years	120 (59 vs. 61)		low-fat diet (incl. animal products) vs. low-fat plus diet (more veggie, legumes, whole grains)	1 month	Blood measures	− lower TC, LDL for low-fat plus (plant-based) diet	+
Macknin et al. (2015)153	Randomized; obese hypercholesterolemic children and their parents	30 (16 vs. 14)		plant-based no added fat diet (PB) vs. American Heart Association Diet (AHA)	1 month	Body weight, blood measures	− lower BMI and hsCRP levels as well as higher waist circumference in the plant-based and no-added fat diet condition in children, − lower cholesterol, LDL and HbA1c in the plant-based and no-added fat diet condition in parents	+/o
Sciarrone et al. (1993)154	Parallel randomized trial, healthy men		20 (10 vs. 10)	lacto-ovo-vegetarian diet vs. omnivorous diet − initial 2 weeks under caloric restriction, afterwards unrestricted	6 weeks	Body weight, blood measures	− no significant differences in body weight, glucose, insulin or catecholamines between groups	o
Alleman et al. (2013)155	Interventional study, healthy subjects		29 (16 vs. 13)	traditional (vegan) vs. modified Daniel Fast diet (incl. daily meat and dairy)	3 weeks	Body weight, blood measures	− no significant weight changes after dietary intervention for neither condition − both diets show improvement of blood lipids, inflammation markers	o
Neacsu et al. (2014)156	Within-subject cross-over design; obese men		20 in total	meat-based high-protein diet vs. vegetarian soy high-protein diet (both diets: 30% protein, 30% fat, 40% carbohydrate)	2 weeks	Body weight, blood measures	− n. s. differences between weight loss and gut hormone profile	o
Koebnick et al. (2004)157	RCT; healthy subjects; site-based study		32 in total	low-fat plant-based (20% fat) vs. control	1 week	Blood measures	− reduced TC, LDL, TG in vegan diet	+
Microbiome
David et al. (2014)35	Within-subject cross-over design, healthy, young volunteers		10	exclusively plant-based diet (unrestricted) vs. nearly exclusively animal-based diet (unrestricted)	5 days	16S rRNA gene sequencing (stool samples)	Higher abundance of bile-tolerant microorganisms (Alistipes, Bilophila, Bacteroides) and decreased levels of Firmicutes (Roseburia, Eubacterium rectale, Ruminococcus bromii).	?
Neurological/psychiatric disease outcomes and brain functions
Karlsson et al. (1994)41	RCT; moderately obese women		60	1300 kcal lacto-vegetarian diet vs. 1300 kcal conventional weight-reducing diet	3, 8, 24 months	Psychological measures incl. mental well-being, functional status; body weight	− no significant differences between groups on psychological measures and BMI	o
Kjeldsen-Kragh et al. (1994)158	RCT; rheumatoid arthritis patients, vegetarian vs. omnivorous diet	53 (27 vs. 26)		− vegetarian diet (fasting 7−10 days, gluten free vegan diets for 3.5 months, afterwards lacto-vegetarian diet vs. - normal omnivorous diet	13 months	General Health Questionnaire	− improvements in psychological distress including depression and anxiety subscores in the vegetarian group	+
Yadav et al. (2016)38	RCT; multiple sclerosis patients	61 (32 vs. 29)		very low-fat plant-based diet: − starchy plant foods, 10% fat, 14% protein, 76% carbohydrates (no meat, fish, eggs, dairy products or vegetable oils) vs. control: − usual diet − assessed by FFQ and meetings with dietician	12 months	Brain MRI, fatigue, body weight, blood sample	− no clear effect on brain MRI outcomes; improvement of fatigue, weight status and metabolic markers in the vegan group	o/+
Bunner et al. (2014)159	RCT; cross-over trial migraine patients; Low-fat vegan vs. placebo	42 in total		Vegan diet: Favored intake of whole grains, lentils, certain vegetables; avoidance of all animal products, nuts and seeds, alcohol, coffee vs. Placebo: 10 mcg alpha-linolenic acid and 10 mcg vitamin E/day	9 months	Headache pain measured with The Patient’s Global Impression of Change	− improvement of migraine during last 2 weeks in the vegan group	+
Kahleova et al. (2013)160	Randomized, open, parallel design, T2DM patients, vegetarian vs. control group	74 (37 vs. 37)		vegetarian diet (−500 kcal/day) vs. control isocaloric conventional anti-diabetic diet (−500 kcal/day)	24 weeks	Quality of life, depressive symptoms, eating behavior	− improved quality of life, dietary restraint and disinhibition and lower depression scores in the vegetarian group	+
Agarwal et al. (2015)23	RCT; overweight and/or T2DM patients; multicomponent worksite intervention; low-fat vegan vs. usual diet	291 at 4 sites; (142 vs. 149)		low-fat vegan (unrestricted): − avoid all animal products, minimize added oils, favor whole grains − vitamin B12 and multivitamin supplements vs. Control: − usual diet; no instruction	18 weeks	Depression, anxiety, fatigue, emotional well-being	− all measures significantly improved in the vegan group	+
Kaartinen et al. (2000)37	Non-randomized; fibromyalgia patients	32 (18 vs. 15)		low-salt, raw vegan diet vs. omnivorous diet	3 months	Disease improvement, urine and blood measures	− less pain, improved joint stiffness and quality of sleep, decreased weight, TC, and urine sodium in the vegan diet group	+
Beezhold et al. (2012)42	Healthy subjects; omnivorous		39 (in locks at 3, i.e. 13 in each group)	control group consuming meat, fish, and poultry daily (OMN) vs. a group consuming fish 3−4 times weekly but avoiding meat and poultry (FISH) vs. a vegetarian group avoiding meat, fish, and poultry (VEG)	2 weeks	Stress, depression, mood, anxiety, blood levels	− decrease in stress, anxiety and improved mood in vegan group − decreased fatty acids, increased n−6 to n−3 ratio and decrease in alpha-linoleic acid in the VEG compared to OMN group	+