A Systematic Review and Meta-Analysis of Changes in Body Weight in Clinical Trials of Vegetarian Diets

Published:January 21, 2015DOI:https://doi.org/10.1016/j.jand.2014.11.016

      Abstract

      In observational studies, vegetarians generally have lower body weights compared with omnivores. However, weight changes that occur when vegetarian diets are prescribed have not been well quantified. We estimated the effect on body weight when vegetarian diets are prescribed. We searched PubMed, EMBASE, and the Cochrane Central Register of Controlled Trials for articles through December 31, 2013. Additional articles were identified from reference lists. We included intervention trials in which participants were adults, interventions included vegetarian diets of ≥4 weeks’ duration without energy intake limitations, and effects on body weight were reported. Two investigators independently extracted data using predetermined fields. Estimates of body weight change, comparing intervention groups to untreated control groups, were derived using a random effects model to estimate the weighted mean difference. To quantify effects on body weight of baseline weight, sex, age, study duration, study goals, type of diet, and study authorship, additional analyses examined within-group changes for all studies reporting variance data. We identified 15 trials (17 intervention groups), of which 4 included untreated controls. Prescription of vegetarian diets was associated with a mean weight change of −3.4 kg (95% CI −4.4 to −2.4; P<0.001) in an intention-to-treat analysis and −4.6 kg (95% CI −5.4 to −3.8; P<0.001) in a completer analysis (omitting missing post-intervention values). Greater weight loss was reported in studies with higher baseline weights, smaller proportions of female participants, older participants, or longer durations, and in studies in which weight loss was a goal. Using baseline data for missing values, I2 equaled 52.3 (P=0.10), indicating moderate heterogeneity. When missing data were omitted, I2 equaled 0 (P=0.65), indicating low heterogeneity. Studies are relatively few, with variable quality. The prescription of vegetarian diets reduces mean body weight, suggesting potential value for prevention and management of weight-related conditions.

      Keywords

      To read this article in full you will need to make a payment

      References

        • Finucane M.M.
        • Stevens G.A.
        • Cowan M.J.
        • et al.
        National, regional, and global trends in body-mass index since 1980: Systematic analysis of health examination surveys and epidemiological studies with 960 country-years and 9.1 million participants.
        Lancet. 2011; 377: 557-567
        • Lewis C.E.
        • McTigue K.M.
        • Burke L.E.
        • et al.
        Mortality, health outcomes, and body mass index in the overweight range: A science advisory from the American Heart Association.
        Circulation. 2009; 119: 3263-3271
        • Berkow S.
        • Barnard N.D.
        Vegetarian diets and weight status.
        Nutr Rev. 2006; 64: 175-188
        • Ornish D.
        • Scherwitz L.W.
        • Billings J.H.
        • et al.
        Intensive lifestyle changes for reversal of coronary heart disease.
        JAMA. 1998; 280: 2001-2007
        • Jenkins D.J.
        • Kendall C.W.
        • Marchie A.
        • et al.
        Direct comparison of a dietary portfolio of cholesterol-lowering foods with a statin in hypercholesterolemic participants.
        Am J Clin Nutr. 2005; 81: 380-387
        • Moher D.
        • Liberati A.
        • Tetzlaff J.
        • Altman D.G.
        • PRISMA Group
        Preferred reporting tems for systematic reviews and meta-analyses: The PRISMA statement.
        PLoS Med. 2009; 6: e1000097
      1. Higgins JPT, Green S, eds. Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 [updated March 2011]. The Cochrane Collaboration. 2011. http://handbook.cochrane.org/. Accessed June 30, 2014.

        • Egger M.
        • Davey Smith G.
        • Phillips A.N.
        Meta-analysis: Principles and procedures.
        BMJ. 1997; 315: 1533-1537
        • Higgins J.P.T.
        • Thompson S.G.
        Quantifying heterogeneity in a meta-analysis.
        Stat Med. 2002; 21: 1539-1558
        • Egger M.
        • Davey Smith G.
        • Schneider M.
        • Minder C.
        Bias in meta-analysis detected by a simple, graphical test.
        BMJ. 1997; 315: 629-634
        • Rosenthal R.
        The file drawer problem and tolerance for null results.
        Psychol Bull. 1979; 86: 638-641
        • Duval S.
        • Tweedie R.
        Trim and fill: A simple funnel plot based method of testing and adjusting for publication bias in meta-analysis.
        Biometrics. 2000; 56: 455-463
        • Lindahl O.
        • Lindwall L.
        • Spangberg A.
        • Stenram A.
        • Ockerman A.
        A vegan regimen with reduced medication in the treatment of hypertension.
        Br J Nutr. 1984; 52: 11-20
        • Kjeldsen-Kragh J.
        • Haugen M.
        • Borchgrevink C.F.
        • et al.
        Controlled trial of fasting and one-year vegetarian diet in rheumatoid arthritis.
        Lancet. 1991; 338: 899-902
        • Johansson G.
        • Holmen A.
        • Persson L.
        • et al.
        The effect of a shift from a mixed diet to a lacto-vegetarian diet on human urinary and fecal mutagenic activity.
        Carcinogenesis. 1992; 13: 153-157
        • Delgado M.
        • Gutierrez A.
        • Cano M.D.
        • Castillo M.J.
        Elimination of meat, fish, and derived products from the Spanish-Mediterranean diet: Effect on the plasma lipid profile.
        Ann Nutr Metab. 1996; 40: 202-211
        • Nenonen M.T.
        • Helve T.A.
        • Rauma A.L.
        • Hanninen O.O.
        Uncooked, lactobacilli-rich, vegan food and rheumatoid arthritis.
        Br J Rheumatol. 1998; 37: 274-281
        • Nicholson A.S.
        • Sklar M.
        • Barnard N.D.
        • Gore S.
        • Sullivan R.
        • Browning S.
        Toward improved management of NIDDM: A randomized, controlled, pilot intervention using a low-fat, vegetarian diet.
        Prev Med. 1999; 29: 87-91
        • Barnard N.D.
        • Scialli A.R.
        • Bertron P.
        • Hurlock D.
        • Edmonds K.
        • Talev L.
        Effectiveness of a low-fat, vegetarian diet in altering serum lipids in healthy premenopausal women.
        Am J Cardiol. 2000; 85: 969-972
        • McDougall J.
        • Bruce B.
        • Spiller G.
        • Westerdahl J.
        • McDougall M.
        Effects of a very low-fat, vegan diet in subjects with rheumatoid arthritis.
        J Altern Complement Med. 2002; 8: 71-75
        • Dansinger M.L.
        • Gleason J.A.
        • Griffith J.L.
        • Selker H.P.
        • Schaefer E.J.
        Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction.
        JAMA. 2005; 293: 43-53
        • Turner-McGrievy G.M.
        • Barnard N.D.
        • Scialli A.R.
        A two-year randomized weight loss trial comparing a vegan diet to a more moderate low-fat diet.
        Obesity (Silver Spring). 2007; 15: 2276-2281
        • Gardner C.D.
        • Kiazand A.
        • Alhassan S.
        • et al.
        Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women.
        JAMA. 2007; 297: 969-977
        • Barnard N.D.
        • Cohen J.
        • Jenkins D.J.
        • et al.
        A low-fat vegan diet and a conventional diabetes diet in the treatment of type 2 diabetes: A randomized, controlled, 74-week clinical trial.
        Am J Clin Nutr. 2009; 89: 1588S-1596S
        • Lisowska A.C.M.
        • Chabasińska M.
        • Przysławski J.
        • Schlegel-Zawadzka M.
        • Madry E.
        • Walkowiak J.
        The influence of 24 months of lactoovovegetarian and vegan diet on nutritional status, energy and macronutrient intake.
        Pediatria Wspolczesna. 2010; 12: 121-125
        • Ferdowsian H.R.
        • Barnard N.D.
        • Hoover V.J.
        • et al.
        A multi-component intervention reduces body weight and cardiovascular risk at a GEICO corporate site.
        Am J Health Promot. 2010; 24: 384-387
        • Mishra S.
        • Xu J.
        • Agarwal U.
        • Gonzales J.
        • Levin S.
        • Barnard N.
        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.
        Eur J Clin Nutr. 2013; 67: 718-724
        • Ornish D.
        Eat More, Weigh Less.
        HarperCollins, New York, NY1993
        • Look AHEAD Research Group
        Eight-year weight losses with an intensive lifestyle intervention: The Look AHEAD study.
        Obesity. 2014; 22: 5-13
        • Yokoyama Y.
        • Nishimura K.
        • Barnard N.D.
        • et al.
        Vegetarian diets and blood pressure: A meta-analysis.
        JAMA Intern Med. 2014; 174: 577-587
        • Craig W.J.
        • Mangels A.R.
        • American Dietetic Association
        Position of the American Dietetic Association: Vegetarian diets.
        J Am Diet Assoc. 2009; 109: 1266-1282
        • Spencer E.A.
        • Appleby P.N.
        • Davey G.K.
        • Key T.J.
        Diet and body mass index in 38,000 EPIC-Oxford meat-eaters, fish-eaters, vegetarians, and vegans.
        Int J Obes Relat Metab Disord. 2003; 27: 728-734
        • Rizzo N.S.
        • Jaceldo-Siegl K.
        • Sabate J.
        • Fraser G.E.
        Nutrient profiles of vegetarian and nonvegetarian dietary patterns.
        J Acad Nutr Diet. 2013; 113: 1610-1619
        • Bell E.A.
        • Rolls B.J.
        Energy density of foods affects energy intake across multiple levels of fat content in lean and obese women.
        Am J Clin Nutr. 2001; 73: 1010-1018
        • Hooper L.
        • Abdelhamid A.
        • Moore H.J.
        • Douthwaite W.
        • Skeaff C.M.
        • Summerbell C.D.
        Effect of reducing total fat intake on body weight: Systematic review and meta-analysis of randomized controlled trials and cohort studies.
        BMJ. 2012; 345: e7666
        • Barnard N.D.
        • Scialli A.R.
        • Turner-McGrievy G.
        • Lanou A.J.
        • Glass J.
        The effects of a low-fat, plant-based dietary intervention on body weight, metabolism, and insulin sensitivity.
        Am J Med. 2005; 118: 991-997
        • Lovejoy J.C.
        • Windhauser M.M.
        • Rood J.C.
        • de la Bretonne J.A.
        Effect of a controlled high-fat versus low-fat diet on insulin sensitivity and leptin levels in African-American and Caucasian women.
        Metabolism. 1998; 47: 1520-1524
        • Hua N.W.
        • Stoohs R.A.
        • Facchini F.S.
        Low iron status and enhanced insulin sensitivity in lacto-ovo vegetarians.
        Br J Nutr. 2001; 86: 515-519
        • Ravussin E.
        • Acheson K.J.
        • Vernet O.
        • Danforth E.
        • Jequier E.
        Evidence that insulin resistance is responsible for the decreased thermic effect of glucose in human obesity.
        J Clin Invest. 1985; 76: 1268-1273
        • Barnard N.D.
        • Scherwitz L.W.
        • Ornish D.
        Adherence and acceptability of a low-fat, vegetarian diet among patients with cardiac disease.
        J Cardiopulm Rehabil Prev. 1992; 12: 423-431
        • Smith C.F.
        • Burke L.E.
        • Wing R.R.
        Vegetarian and weight-loss diets among young adults.
        Obes Res. 2000; 8: 123-129
        • Barnard N.D.
        • Scialli A.R.
        • Turner-McGrievy G.M.
        • Lanou A.J.
        Acceptability of a very-low-fat, vegan diet compares favorably to a more moderate low-fat diet in a randomized, controlled trial.
        J Cardiopulm Rehab. 2004; 24: 229-235
        • Barnard N.D.
        • Gloede L.
        • Cohen J.
        • et al.
        A low-fat vegan diet elicits greater macronutrient changes, but is comparable in adherence and acceptability, compared with a more conventional diabetes diet among individuals with type 2 diabetes.
        J Am Diet Assoc. 2009; 109: 263-272
        • Katcher H.I.
        • Ferdowsian H.R.
        • Hoover V.J.
        • Cohen J.L.
        • Barnard N.D.
        A worksite vegan nutrition program is well-accepted and improves health-related quality of life and work productivity.
        Ann Nutr Metab. 2010; 56: 245-252
        • Rouse I.L.
        • Beilin L.J.
        • Armstrong B.K.
        • Vandongen R.
        Blood-pressure-lowering effect of a vegetarian diet: Controlled trial in normotensive subjects.
        Lancet. 1983; 1: 5-10
        • Margetts B.M.
        • Beilin L.J.
        • Armstrong B.K.
        • Vandongen R.
        Vegetarian diet in the treatment of mild hypertension: A randomized controlled trial.
        J Hypertens Suppl. 1985; 3: S429-S431
        • Burke L.E.
        • Hudson A.G.
        • Warziski M.T.
        • et al.
        Effects of a vegetarian diet and treatment preference on biochemical and dietary variables in overweight and obese adults: A randomized clinical trial.
        Am J Clin Nutr. 2007; 86: 588-596
        • Jenkins D.J.
        • Wong J.M.
        • Kendall C.W.
        • et al.
        The effect of a plant-based low-carbohydrate (“Eco-Atkins”) diet on body weight and blood lipid concentrations in hyperlipidemic subjects.
        Arch Intern Med. 2009; 169: 1046-1054
        • Diabetes Prevention Program Research Group
        The Diabetes Prevention Program: Description of lifestyle intervention.
        Diabetes Care. 2002; 25: 2165-2171

      Biography

      N. D. Barnard is an adjunct associate professor, The George Washington University School of Medicine, Washington, DC.

      Biography

      S. M. Levin is director of nutrition education, Physicians Committee for Responsible Medicine, Washington, DC.

      Biography

      Y. Yokoyama is a project assistant professor, Graduate School of Media and Governance, Keio University, Kanagawa, Japan; at the time of the study, she was a research fellow, Japan Society for the Promotion of Science and the Department of Preventive Medicine and Epidemiology, National Cerebral and Cardiovascular Center, Osaka, Japan.