Introduction
As a chronic disease, obesity is one of the biggest challenges for the health care system, which is associated with heart diseases, diabetes mellitus, high blood pressure, and cancer [1, 2]. The increase in the prevalence of obesity is due to having an unhealthy lifestyle, inactivity, and reduced physical activity [3]. Lifestyle and health-related behaviors (such as poor diet, inactivity, and tobacco or alcohol use) are strongly associated with morbidity and mortality in many chronic diseases worldwide [5]. By proper diet, regular physical activity, and lifestyle changes, it is possible to adjust the body composition and lose weight. Dietary modification improves clinical markers of cardiovascular risk, reduces body weight, improves body composition, and lowers blood glucose levels [6].
One effective dietary approach to combating obesity is a plant-based diet (PBD) [7, 8, 9]. It has been shown that a PBD is useful in the prevention and treatment of many diseases such as cardiovascular diseases, diabetes, cancer, osteoporosis, kidney disease, dementia, as well as gallstone disease and rheumatoid arthritis [6, 12-15]. Another approach is exercise, which is associated with several metabolic outcomes [16]. Significant changes in the body composition can be obtained by reducing the fat mass and increasing the fat-free mass. Exercise leads to a healthier body composition, especially for people with larger body fat stores [17], and reduces various health risk factors, especially factors related to cardiovascular diseases and metabolic syndrome [18]. It causes the release of lipolytic hormones, including growth hormone and epinephrine, which may facilitate more energy consumption after exercise and fat oxidation [19].
Considering the important role of PBD and aerobic exercise on improving body composition and health status, this review and meta-analysis aim to investigate the combined effects of aerobic exercise and PBD on body composition in overweight and obese adults.

Methods
This is a systematic review and meta-analysis study. A search was conducted in PubMed, Web of Science, Scopus, and Google Scholar databases on related studies published in English until February 2023 using the keywords: vegetarian diet, plant-based diet, exercise, aerobic exercise, aerobic training, endurance exercise, endurance training, body composition, adipocyte, fat percent, waist circumference, adult, body mass index, overweight, and obesity. 
The inclusion criteria for articles were: 1- Studies published in English; 2- Studies conducted on overweight and obese adults; 3- Studies examining the combined effect of aerobic exercise and PBD; 4- Studies measuring body mass index, body fat percentage, and waist circumference; 5- Cohort studies and randomized control trials; and 6- Studies with an intervention duration of more than 2 weeks. Animal studies, theses, conference articles, crossover studies and studies with an intervention period of less than 2 weeks were excluded. The initial review of the articles was done by two authors. 
Evaluation of the quality of studies was done using the PEDro scale (22). The criteria included: 1-  eligibility criteria were specified, 2- subjects were randomly allocated to groups, 3-  there was blinding of all assessors , 4- measures of at least one key outcome were obtained from more than 85% of the subjects, 5- data for at least one key outcome was analyzed by “intention to treat”, 6- results of between-group statistical comparisons were reported for at the main study variable, and 7- results of mean, standard deviations, and p values were reported. The items are answered by yes or no. The total score ranges from 0 to 7, with higher scores indicating higher quality.
A meta-analysis was performed to compare the effects of aerobic exercise and PBD on body composition. Data analysis was performed using a random effect model. Also, the confidence interval of 95% was considered. Also, the I2 test was used to measure heterogeneity. 

Results
The initial search yielded 1052 articles. After removing duplicates (n=218 ), and after screening the titles and abstracts, 33 articles were selected for full text screening. After screening the full texts, 14 articles were excluded from the present study. Finally, 19 studies were included in the review. There were 12 studies (14 interventions) for body weight variable, 13 studies (13 interventions) for BMI, 5 studies (7 interventions) for body fat percentage, and 5 studies (5 interventions) for waist circumference. The results of checking the quality using PEDro scale showed that the quality score of the articles was in a range of 3-6.
The meta-analysis of 19 studies on 3279 adults showed that combined aerobic exercise and PBD significantly reduced body weight (weighted mean difference [WMD]=-5.05 kg; 95%CI: -6.05 to -4.05, P=0.001), body mass index (WMD=-1.29 kg/m2, 95%CI: -1.65 to -0.92, P=0.001), body fat percentage (WMD=-3.04%, 95%CI: -4.13 to -1.95, P=0.001), and waist circumference (WMD=-3.36 cm, 95%CI: -5.98 to -0.68, P=0.01) in adults with overweight and obesity. 

Conclusion
The combined aerobic exercise and PBD cause a significant decrease in body weight with a high effect size (-5.05), a decrease in BMI with a high effect size (-1.29), a decrease in waist circumference with a high effect size (-3.36) and also decrease in body fat percentage with high effect size (-3.04) in overweight and obese adults. The findings highlighted the important role of exercise and PBD in reducing body fat and improving body composition. Therefore, aerobic exercise combined with PBD is recommended as a non-pharmacological solution to lose weight and improve body composition for overweight and obese adults.

Ethical Considerations
Compliance with ethical guidelines
This article is a meta-analysis with no human or animal sample.

Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors. 

Authors' contributions
All authors equally contributed to preparing this article.

Conflicts of interest
The authors declared no conflict of interest.


References

1. Liu Y, Douglas PS, Lip GYH, Thabane L, Li L, Ye Z, et al. Relationship between obesity severity, metabolic status and cardiovascular disease in obese adults. European Journal of Clinical Investigation. 2023; 53(3):e13912. [DOI:10.1111/eci.13912] [PMID]
2. Pati S, Irfan W, Jameel A, Ahmed S, Shahid RK. Obesity and cancer: A current overview of epidemiology, pathogenesis, outcomes, and management. Cancers. 2023; 15(2):485. [DOI:10.3390/cancers15020485] [PMID] [PMCID]
3. Suazo EMH, Chagoya LAM, Gutierrez LGF. Improvement on biometrics in individuals undergoing a 10 and 21-day lifestyle intervention in a lifestyle medicine clinic in Mexico. Journal of Lifestyle Medicine. 2021; 11(2):66-73. [DOI:10.15280/jlm.2021.11.2.66] [PMID] [PMCID]
4. Klimis H, Thiagalingam A, McIntyre D, Marschner S, Von Huben A, Chow CK. Text messages for primary prevention of cardiovascular disease: The TextMe2 randomized clinical trial. American Heart Journal. 2021; 242:33-44. [DOI:10.1016/j.ahj.2021.08.009] [PMID]
5. Lee KS, Lee JK, Yeun YR. Effects of a 10-day intensive health promotion program combining diet and physical activity on body composition, physical fitness, and blood factors of young adults: A randomized pilot study. Medical Science Monitor: international Medical Journal of Experimental and Clinical Research. 2017; 23:1759-67. [DOI:10.12659/MSM.900515] [PMID] [PMCID]
6. Bhardwaj S, Misra A, Gulati S, Anoop S, Kamal VK, Pandey RM. A randomized controlled trial to evaluate the effects of high Protein Complete (lActo) VEgetaRian (PACER) diet in non-diabetic obese Asian Indians in North India. Heliyon. 2018; 3(12):e00472. [DOI:10.1016/j.heliyon.2017.e00472] [PMID] [PMCID]
7. Turner-McGrievy G, Mandes T, Crimarco A. A plant-based diet for overweight and obesity prevention and treatment. Journal of Geriatric Cardiology: JGC. 2017; 14(5):369-74. [PMID]
8. Asoudeh F, Mousavi SM, Keshteli AH, Hasani-Ranjbar S, Larijani B, Esmaillzadeh A, et al. The association of plant-based dietary pattern with general and abdominal obesity: A large cross-sectional study. Journal of Diabetes & Metabolic Disorders. 2023; 22(1):469-77. [DOI:10.1007/s40200-022-01166-1] [PMID] [PMCID]
9. Jakše B, Jakše B, Pinter S, Pajek J, Fidler Mis N. Whole-food plant-based lifestyle program and decreased obesity. American Journal of Lifestyle Medicine. 2022; 16(3):260-70. [DOI:10.1177/1559827620949205] [PMID] [PMCID]
10. Koeder C, Kranz RM, Anand C, Husain S, Alzughayyar D, Schoch N, et al. Effect of a 1-year controlled lifestyle intervention on body weight and other risk markers (the Healthy Lifestyle Community Programme, cohort 2). Obesity Facts. 2022; 15(2):228-39. [DOI:10.1159/000521164] [PMID] [PMCID]
11. Long Y, Ye H, Yang J, Tao X, Xie H, Zhang J, et al. Effects of a vegetarian diet combined with aerobic exercise on glycemic control, insulin resistance, and body composition: A systematic review and meta-analysis. Eating and Weight Disorders. 2023; 28(1):9. [DOI:10.1007/s40519-023-01536-5] [PMID] [PMCID]
12. Weston LJ, Kim H, Talegawkar SA, Tucker KL, Correa A, Rebholz CM. Plant-based diets and incident cardiovascular disease and all-cause mortality in African Americans: A cohort study. PLoS Medicine. 2022; 19(1):e1003863. [DOI:10.1371/journal.pmed.1003863] [PMID] [PMCID]
13. del Carmen Fernández-Fígares Jiménez M. Plant foods, healthy plant-based diets, and type 2 diabetes: A review of the evidence. Nutrition Reviews. 2024; 82(7):929-48. [DOI:10.1093/nutrit/nuad099] [PMID]
14. DeClercq V, Nearing JT, Sweeney E. Plant-based diets and cancer risk: What is the evidence? Current Nutrition Reports. 2022; 11(2):354-69. [DOI:10.1007/s13668-022-00409-0] [PMID]
15. Dai ZJ. A literature review on plant-based foods and dietary quality in knee osteoarthritis. European Journal of Rheumatology. 2022; 11(Suppl 1):S32–40. [PMID]
16. Salonen MK, Wasenius N, Kajantie E, Lano A, Lahti J, Heinonen K, et al. Physical activity, body composition and metabolic syndrome in young adults. Plos One. 2015; 10(5):e0126737. [DOI:10.1371/journal.pone.0126737] [PMID] [PMCID]
17. Westerterp KR. Exercise, energy balance and body composition. European Journal of Clinical Nutrition. 2018; 72(9):1246-50. [DOI:10.1038/s41430-018-0180-4] [PMID] [PMCID]
18. Dashti N, Rezaeian N, Karimi M, Kooroshfard N. [The effect of high intensity interval training on serum levels of Osteopontin and insulin resistance index in sedentary overweight and obese women (Persian)]. Journal of Sport and Exercise Physiology. 2021; 14(2):115-26. [DOI:10.52547/joeppa.14.2.115]
19. Salimi Avansar M. [Effect of HIIT training on the Levels of Omentin-1 and Body composition characteristics in Sedentary Obese Men(Persian)]. Journal of Sport and Exercise Physiology. 2017; 10(2):59-68. [DOI:10.48308/joeppa.2017.98884]
20. Wan X, Wang W, Liu J, Tong T. Estimating the sample mean and standard deviation from the sample size, median, range and/or interquartile range. BMC Medical Research Methodology. 2014; 14:135. [DOI:10.1186/1471-2288-14-135] [PMID] [PMCID]
21. Higgins JP, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, et al. Cochrane handbook for systematic reviews of interventions. London: Cochrane; 2019. [DOI:10.1002/9781119536604]
22. De Morton NA. The PEDro scale is a valid measure of the methodological quality of clinical trials: A demographic study. Australian Journal of Physiotherapy. 2009; 55(2):129-33. [DOI:10.1016/S0004-9514(09)70043-1] [PMID]
23. Higgins JP, Thompson SG, Deeks JJ, Altman DG. Measuring inconsistency in meta-analyses. BMJ. 2003; 327(7414):557-60. [DOI:10.1136/bmj.327.7414.557] [PMID] [PMCID]
24. Copas J, Shi JQ. Meta-analysis, funnel plots and sensitivity analysis. Biostatistics. 2000; 1(3):247-62. [DOI:10.1093/biostatistics/1.3.247] [PMID]
25. Egger M, Davey Smith G, Schneider M, Minder C. Bias in meta-analysis detected by a simple, graphical test. BMJ. 1997; 315(7109):629-34. [DOI:10.1136/bmj.315.7109.629] [PMID] [PMCID]
26. Kahleova H, Matoulek M, Malinska H, Oliyarnik O, Kazdova L, Neskudla T, et al. Vegetarian diet improves insulin resistance and oxidative stress markers more than conventional diet in subjects with Type 2 diabetes. Diabetic Medicine. 2011; 28(5):549-59. [DOI:10.1111/j.1464-5491.2010.03209.x] [PMID] [PMCID]
27. Kent L, Morton D, Rankin P, Ward E, Grant R, Gobble J, et al. The effect of a low-fat, plant-based lifestyle intervention (CHIP) on serum HDL levels and the implications for metabolic syndrome status-a cohort study. Nutrition & Metabolism. 2013; 10(1):58. [DOI:10.1186/1743-7075-10-58] [PMID] [PMCID]
28. Ornish D, Brown SE, Scherwitz LW, Billings JH, Armstrong WT, Ports TA, et al. Can lifestyle changes reverse coronary heart disease? The Lifestyle Heart Trial. The Lancet. 1990; 336(8708):129-33. [DOI:10.1016/0140-6736(90)91656-U] [PMID]
29. Cairo J, Williams L, Bray L, Goetzke K, Perez AC. Evaluation of a mobile health intervention to improve wellness outcomes for breast cancer survivors. Journal of Patient-Centered Research and Reviews. 2020; 7(4):313-22. [DOI:10.17294/2330-0698.1733] [PMID] [PMCID]
30. Chainani-Wu N, Weidner G, Purnell DM, Frenda S, Merritt-Worden T, Pischke C, et al. Changes in emerging cardiac biomarkers after an intensive lifestyle intervention. The American Journal of Cardiology. 2011; 108(4):498-507. [DOI:10.1016/j.amjcard.2011.03.077] [PMID]
31. Diehl HA. Coronary risk reduction through intensive community-based lifestyle intervention: The Coronary Health Improvement Project (CHIP) experience. The American Journal of Cardiology. 1998; 82(10B):83T-7T. [DOI:10.1016/S0002-9149(98)00746-2] [PMID]
32. Dod HS, Bhardwaj R, Sajja V, Weidner G, Hobbs GR, Konat GW, et al. Effect of intensive lifestyle changes on endothelial function and on inflammatory markers of atherosclerosis. The American Journal of Cardiology. 2010; 105(3):362-7. [DOI:10.1016/j.amjcard.2009.09.038] [PMID]
33. Kahleova H, Matoulek M, Bratova M, Malinska H, Kazdova L, Hill M, et al. Vegetarian diet-induced increase in linoleic acid in serum phospholipids is associated with improved insulin sensitivity in subjects with type 2 diabetes. Nutrition & Diabetes. 2013; 3(6):e75-e. [DOI:10.1038/nutd.2013.12] [PMID] [PMCID]
34. Kent L, Grant R, Watts G, Morton D, Rankin P. HDL subfraction changes with a low-fat, plant-based Complete Health Improvement Program (CHIP). Asia Pacific Journal of Clinical Nutrition. 2018; 27(5):1002-9. [Link]
35. Koertge J, Weidner G, Elliott-Eller M, Scherwitz L, Merritt-Worden TA, Marlin R, et al. Improvement in medical risk factors and quality of life in women and men with coronary artery disease in the Multicenter Lifestyle Demonstration Project. The American Journal of Cardiology. 2003; 91(11):1316-22. [DOI:10.1016/S0002-9149(03)00320-5] [PMID]
36. Marshall DA, Walizer EM, Vernalis MN. Achievement of heart health characteristics through participation in an intensive lifestyle change program (Coronary Artery Disease Reversal Study). Journal of Cardiopulmonary Rehabilitation and Prevention. 2009; 29(2):84-94. [DOI:10.1097/HCR.0b013e31819a00b2] [PMID]
37. Morton D, Rankin P, Kent L, Sokolies R, Dysinger W, Gobble J, et al. The Complete Health Improvement Program (CHIP) and reduction of chronic disease risk factors in Canada. Canadian Journal of Dietetic Practice and Research. 2014; 75(2):72-7. [DOI:10.3148/75.2.2014.72] [PMID]
38. Ornish D, Scherwitz LW, Billings JH, Brown SE, Gould KL, Merritt TA, et al. Intensive lifestyle changes for reversal of coronary heart disease. JAMA. 1998; 280(23):2001-7. [DOI:10.1001/jama.280.23.2001] [PMID]
39. Pischke CR, Weidner G, Elliott-Eller M, Scherwitz L, Merritt-Worden TA, Marlin R, et al. Comparison of coronary risk factors and quality of life in coronary artery disease patients with versus without diabetes mellitus. The American Journal of Cardiology. 2006; 97(9):1267-73. [DOI:10.1016/j.amjcard.2005.11.051] [PMID]
40. Pischke CR, Weidner G, Elliott-Eller M, Ornish D. Lifestyle changes and clinical profile in coronary heart disease patients with an ejection fraction of≤ 40% or> 40% in the Multicenter Lifestyle Demonstration Project. European Journal of Heart Failure. 2007; 9(9):928-34. [DOI:10.1016/j.ejheart.2007.05.009] [PMID]
41. Świątkiewicz I, Di Somma S, De Fazio L, Mazzilli V, Taub PR. Effectiveness of intensive cardiac rehabilitation in high-risk patients with cardiovascular disease in real-world practice. Nutrients. 2021; 13(11):3883. [DOI:10.3390/nu13113883] [PMID] [PMCID]
42. Toobert DJ, Glasgow RE, Radcliffe JL. Physiologic and related behavioral outcomes from the Women›s Lifestyle Heart Trial. Annals of Behavioral Medicine. 2000; 22(1):1-9. [DOI:10.1007/BF02895162] [PMID]
43. Kopelman PG. Obesity as a medical problem. Nature. 2000; 404(6778):635-43. [DOI:10.1038/35007508] [PMID]
44. Telles S, Naveen VK, Balkrishna A, Kumar S. Short term health impact of a yoga and diet change program on obesity. Medical Science Monitor. 2010; 16(1):CR35-40. [PMID]
45. Null G, Feldman M. Comprehensive lifestyle interventions in the community: A preliminary analysis. Age. 1996; 19(3):91-100. [DOI:10.1007/BF02434088]
46. Shamizadeh M, Zolfaghari MR, Fattahi A. [Effect of eight weeks of aerobic and resistance training on adropin, spexin, and TNFα levels, as well as insulin resistance indices, in obese men with type 2 diabetes (Persian)]. Journal of Ilam University of Medical Sciences. 2023; 31(5):70-84. [Link]
47. Slavícek J, Kittnar O, Fraser GE, Medová E, Konecná J, Zizka R, et al. Lifestyle decreases risk factors for cardiovascular diseases. Central European Journal of Public Health. 2008; 16(4):161-4. [DOI:10.21101/cejph.a3474] [PMID] [PMCID]
48. Lotfi M, Nouri M, Turki Jalil A, Rezaianzadeh A, Babajafari S, Ghoddusi Johari M, et al. Plant-based diets could ameliorate the risk factors of cardiovascular diseases in adults with chronic diseases. Food Science & Nutrition. 2023; 11(3):1297-308. [DOI:10.1002/fsn3.3164] [PMID] [PMCID]

49. Tsaban G, Yaskolka Meir A, Rinott E, Zelicha H, Kaplan A, Shalev A, et al. The effect of green Mediterranean diet on cardiometabolic risk; a randomised controlled trial. Heart. 2021; 107(13):1054-61. [DOI:10.1136/heartjnl-2020-317802] [PMID]
50. Del Bo' C, Perna S, Allehdan S, Rafique A, Saad S, AlGhareeb F, et al. Does the Mediterranean diet have any effect on lipid profile, central obesity and liver enzymes in Non-Alcoholic Fatty Liver Disease (NAFLD) subjects? A systematic review and meta-analysis of randomized control trials. Nutrients. 2023; 15(10):2250. [DOI:10.3390/nu15102250] [PMID] [PMCID]
51. Key TJ, Appleby PN, Rosell MS. Health effects of vegetarian and vegan diets. Proceedings of the Nutrition Society. 2006; 65(1):35-41. [DOI:10.1079/PNS2005481] [PMID]