The Effect of Vegetarian Diets on Iron Status in Adults a Systematic Review and Meta-analysis
Nutrients. 2020 Jun; 12(six): 1604.
Effects of Vegetarian Diets on Claret Pressure level Lowering: A Systematic Review with Meta-Analysis and Trial Sequential Analysis
Hong Chuan Loh
2Clinical Research Centre, Infirmary Seberang Jaya, Ministry building of Wellness Malaysia, Perai 13700, Penang, Malaysia; moc.liamg@nauhcgnohhol
Siew Mooi Ching
1Department of Family Medicine, Kinesthesia of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang 43400, Selangor, Malaysia; moc.oohay@iew_iak_eel (M.W.50.); ym.ude.mpu@gnihc_ms (S.G.C.); ym.ude.mpu@nivank (Northward.G.D.)
threeMalaysian Enquiry Constitute on Ageing, University Putra Malaysia, Serdang 43400, Selangor, Malaysia
ivDepartment of Medical Sciences, Schoolhouse of Healthcare and Medical Sciences, Sunway University, Bandar Sunway 47500, Selangor, Malaysia
Navin Kumar Devaraj
1Department of Family Medicine, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang 43400, Selangor, Malaysia; moc.oohay@iew_iak_eel (Thou.W.L.); ym.ude.mpu@gnihc_ms (Southward.1000.C.); ym.ude.mpu@nivank (N.Chiliad.D.)
3Malaysian Research Found on Ageing, University Putra Malaysia, Serdang 43400, Selangor, Malaysia
Fan Kee Hoo
fiveSection of Medicine, Kinesthesia of Medicine and Health Sciences, Academy Putra Malaysia, Serdang 43400, Selangor, Malaysia
Received 2020 Feb 28; Accustomed 2020 Mar 27.
Abstract
The benign furnishings of a vegetarian diet on claret pressure (BP) control have been reported in previous systematic reviews; all the same, and then far, their relative effectiveness is not well established. Here, we performed a systematic review together with trial sequential analysis to decide the result of a vegetarian nutrition on the reduction of blood pressure. We searched the randomized controlled trial (RCT) through Medline, PubMed and Cochrane Fundamental Register. Fifteen eligible RCTs with 856 subjects were entered into the assay. The pooled results demonstrated that vegetarian diet consumption significantly lowered the systolic blood force per unit area (weighted mean difference (WMD), −ii.66 mmHg (95% confidence interval (CI) = −3.76, −1.55, p < 0.001) and diastolic BP was WMD, −one.69 95% CI = −2.97, −0.41, p < 0.001) as compared to an omnivorous diet. In subgroup analysis, a vegan diet demonstrated a greater reduction in systolic BP (WMD, −iii.12 mmHg; 95% CI = −4.54, −1.70, p < 0.001) equally compared with a lacto-ovo-vegetarian diet (WMD, −1.75 mmHg, 95% CI −5.38, 1.88, p = 0.05). The vegan diet has showed a similar trend in terms of diastolic claret force per unit area reduction (WMD, −1.92 mmHg (95% CI = −3.18, −0.66, p < 0.001) but those with a lacto-ovo-vegetarian nutrition showed no changes in diastolic BP reduction (WMD, 0.00, 95% CI = 0.00, 0.00), p = 0.432). In decision, vegetarian diets are associated with significant reductions in BP compared with omnivorous diets, suggesting that they may play a key role in the primary prevention and overall direction of hypertension.
Keywords: hypertension, diet, vegan, vegetarian, institute-based diets
1. Introduction
It is estimated that most 26% of the world's population (957–987 million) were affected with hypertension in 2000, with 333 meg from developed countries and 639 million from developing countries [1]. It is an escalating trend, rising from 594 one thousand thousand in 1975 to one.xiii billion in 2015, and this mainly now occurs in low-income and middle-income countries. This global shifting has resulted from the increase in population growth and unprecedented process of crumbling [2].
High blood pressure or hypertension is defined as systolic blood pressure level of 140 mmHg or higher, and diastolic blood pressure of 90 mmHg or higher [3]. It is an independent and major risk factor for cardiovascular disease and chronic kidney failure [4,5,6,7]. Patients with hypertension take a twofold to threefold higher risk for eye illness or stroke, every bit compared with those without hypertension [4,five]. In addition, patients with hypertension are more than likely to develop type two diabetes, and patients with type 2 diabetes also have hypertension as well [viii,nine]. Patients having both hypertension and diabetes possess the highest risk of developing a stroke issue and, in particular, having a fatal stroke [six]. On top of that, hypertension alone contributed about 29% of the underlying cause of end-stage renal disease [vii].
Vegetarian diets are defined as dietary patterns that are determined by the level of animal food intake, and tin can be classified into several subtypes. Firstly, the vegan diet is defined equally plant-based nutrition merely; secondly, the lacto-ovo-vegetarian diet refers to diet that is without meat but may include eggs and/or dairy products; thirdly, the pescovegetarian nutrition may contain fish, but with other meats but taken < in one case/month; and the semivegetarian diet contains meats besides fish occasionally, but these are simply taken < one time/week [10]. Vegetarian diets mostly have a higher diet quality than nonvegetarian diets [xi]. This is due to the fact that the vegetarian diets have a higher portion of glutamic acid and constitute-based protein, which has blood-pressure level-lowering issue [12,13,xiv]. Besides, the higher fiber, antioxidants content, potassium content and lower saturated fat and sodium content in vegetarian diets can contribute to a lower trunk mass index and claret pressure readings [15,16,17]. Vegetarian diet reduces high blood pressure via several mechanisms, such equally by improving blood viscosity, vasodilation and insulin sensitivity; by altering the baroreceptors, renin-angiotensin and sympathetic nervous organisation; by its anti-oxidant and anti-inflammatory properties and past changing the colony and strain of gut microflora [eighteen,nineteen,20,21,22,23]. Thus, many studies have shown that dietary patterns with a lower meat intake like the vegetarian nutrition is associated with a lower rate of non-communicable disease particularly hypertension [16,17] and contributed to a better health outcome and longer life expectancy.
However, to date, previous studies have offered alien results regarding this topic [24,25], and, to our knowledge, in that location has not been any quantitative try to summarize the precise effect of vegetarian diets on blood pressure reduction. Thus, nosotros have performed a trial sequential analysis (TSA) to decide whether the currently available evidence was sufficient and conclusive on this important discipline matter. A meta-analysis of studies with TSA methodology could elucidate the associations betwixt vegetarian diets and blood pressure lowering from estimation of the consequence size regarding the benefits of vegetarian diets consumption compared with omnivorous diets by looking at whether adequate sample ability size of the randomized controlled trials take been achieved and whether the conclusions are valid or non.
ii. Methods
The protocol was registered in the Medical Research and Ethics Committee, Ministry of Wellness Malaysia (registration number: NMRR-20-250-53210) on 25 Feb 2020. The reporting followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines [26].
2.1. Data Sources
Nosotros searched three major commendation databases (Medline, PubMed and Cochrane Cardinal Register of controlled trials) and included all relevant citations regardless of data of publication from inception to 6 Jan 2020. We besides used frontwards and backward citation from the included studies to search for relevant studies. The search strategy is shown in Table S1.
two.two. Intervention and Control Grouping Definitions
The intervention group was defined as participants who were on a lacto-ovo-vegetarian nutrition (defined as those excluding meat, poultry and fish, and consuming eggs and dairy products) or a vegan diet (defined every bit excluding brute-derived food products such as meat, fish, poultry, eggs, and milk) for at to the lowest degree two weeks. The control group was defined as participants who were on an omnivorous nutrition (divers equally those who consume meat, poultry, fish, eggs, and dairy products).
two.3. Study Selection
We included randomized controlled trials of two weeks' follow-upward duration comparing the upshot of vegetarian diets (which included vegan to lacto-ovo-vegetarian) with not-vegetarian diets on systolic and diastolic claret pressure as a main or secondary outcomes. The included studies had to be published in English language or have an English translation. Studies were excluded if at that place was no vegetarian intervention, no nonvegetarian control, or no suitable outcome data.
2.4. Data Extraction
Two investigators (KWL and HCL) independently reviewed and extracted relevant information from each of the included studies. A standardized grade was used to extract data on the following variables: commencement author, publication yr, country, baseline characteristics of the study population, baseline and follow-upward blood pressure levels, and changes of blood pressure in hateful ± standard deviation. All discrepancies and disagreements were resolved through consensus.
2.five. Data Syntheses
Hateful differences in systolic and diastolic blood pressure betwixt patients assigned to receive the vegetarian and comparators diets were calculated using a meta-analysis with random-effects model and trial sequential analysis. Estimates of net changes in claret pressure associated with the consumption of vegetarian diets were combined using a random effects model and the result was reported with a 95% conviction interval with a two-sided p value of <0.05, which was considered as statistically pregnant. Meta-analyses were conducted using Open Meta Analyst software [27]. Nosotros performed trial sequential analysis for primary outcome with the random-effect (DL) model using the TSA software parcel [28]. Meta-analysis is the statistical procedure for combining data from multiple studies in guild to determine overall trends, however meta-analysis may have type I errors due to systematic bias or random errors (for instance, sparse data and repeated significance testing) [28]. TSA is a methodology that combines sample sizes of all included trials with the threshold of statistical significance, which quantifies the statistical reliability of data in the cumulative meta-analysis adjusting the significance levels for sparse data and repetitive testing on accumulating data [29]. Therefore, the results in meta-assay are more reliable and conclusive with a TSA, equally it helps to reveal insufficient information size and potential faux positive results in the meta-analysis [30].
We used mean ± standard divergence (SD) to express our outcomes. If the mean deviation and SD were non provided, the mean was calculated by subtracting the mean of baseline measurement from the corresponding hateful of mail intervention measurement; SD was imputed from the cease point measurement. If the mean deviation was provided, but the SD was not, the latter was imputed either from the end bespeak measurement or calculated using the confidence intervals with the formulas "SQRT (sample size) × (upper conviction interval-lower confidence interval)/(T.INV.2T (0.05, $D$2-ane) × 2)" proposed past [31]; this part was used to summate estimated SD with Excel.
2.half-dozen. Risk of Bias Assessment
Included trials were independently assessed by 2 investigators (KWL and HCL) for risk of bias using the Cochrane Risk of Bias Tool [32,33]. Assessment was washed beyond v domains of bias (Bias arising from the randomization process, bias due to deviations from intended interventions, bias due to missing outcome data, bias in measurement of the outcome and bias in selection of the reported outcome). The hazard of bias was assessed as either low risk (proper methods taken to reduce bias), some business concern (insufficient information provided to determine the bias level), or high run a risk (improper methods creating bias). All discrepancies and disagreement were resolved through consensus, or, where necessary, by the third (SMC) and 4th author (NKD). A graph and a summary of risk of bias were generated using Review Manager (Rev-Human being), version 5.three (Nordic Cochrane Conte, Cochrane Collaboration, Copenhagen, Kingdom of denmark).
2.7. Grading of the Evidence
The Grading of Recommendations Assessment, Evolution, and Evaluation (Class) approach was used to assess the certainty of the bear witness [34,35,36,37,38]. The certainty of the evidence was graded as loftier, moderate, depression, or very low. Randomized controlled trials received an initial grade of high of evidence by default, or high inconsistency (I2 > 75%, p value < 0.05) [39], indirectness (presence of factors that limit the generalizability of the results) [forty], imprecision (the 95% CI for weighted mean difference were wide) [41], and/or publication bias (pregnant prove of small-study effects) [42].
3. Results
3.i. Search Results
The literature search and selection procedure is shown in Effigy ane. We identified a full of 2626 studies afterwards removing duplicates, 2571 of which were excluded based on review of the title and/or abstract. The remaining 55 studies were retrieved and reviewed in total, of which 40 were excluded based on pick criteria. A total of 15 studies involving 856 individuals met the eligibility criteria and were included in the final analyses [43,44,45,46,47,48,49,50,51,52,53,54,55,56,57].
Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) catamenia diagram of the literature screening process.
3.two. Trials Characteristics
Characteristics of the fifteen included studies are shown in Table one. Fourteen of the trials were conducted among adults [43,44,45,46,47,48,fifty,51,52,53,54,55,56,57] and i was in children [49]. The intervention grouping in five of the studies was receiving a lacto-ovo-vegetarian diet [47,52,54,55,56], and the intervention group in 10 of the studies was receiving a vegan diet [43,44,45,46,48,49,50,51,53,57]. Viii studies were conducted among participants with diabetes [43,44,46,48,50,51,53,57] and seven studies were amongst participants without diabetes [45,47,49,52,54,55,56]. More than half of studies were conducted in either the United States [43,44,45,46,47,49,50,51,53,56], Australia [52,54,55], New Zealand [57] or South korea [48]. The clinical trials had a follow-up duration that ranged from iii to 74 weeks. The overall baseline BP was 125.5 mmHg (108–149.v mmHg)/75.three mmHg (65–86 mmHg). The overall postinterventional BP was 122.6 mmHg (106.4–147 mmHg)/73.8 mmHg (64–83.5 mmHg).
Table one
Characteristics of trial.
| Starting time Author (Vegetarian vs. Control) | Year | Expanse | Age, Mean ± SD (Range) | Gender, northward (%) | Medication (%) | Baseline BMI, Mean ± SD (Range) | Energy Intake Divergence † | Weight Difference † | Diabetes | Vegetarian/Vegan | Command Group | Trial Elapsing | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Vegan | Conventional Diet | Vegan | Conventional Nutrition | Vegan | Conventional Diet | Vegan | Conventional Diet | |||||||||
| Barnard et al., 2009 (Depression-fat vegan diet vs. conventional diabetes diet) | 2013 | The states | 56.7 ± 9.8 (35–82) | 54.6 ± 10.two (27–eighty) | Male, 22 (45); Female, 27 (55) | Male person, 17 (34); Female person, 33 (66) | DM (78); HPT (76); LIPID (54) | DM (69); HPT (63); LIPID (55) | N/A | N/A | 0.90 | 0.25 | With Diabetes | Vegan | meat nutrition | 74 weeks |
| Barnard et al., 2017 (Low-fatty vegan diet vs. portion-controlled eating plan) | 2017 | USA | 61 (41–79) | 61 (30–75) | Male, viii (38); Female, xiii (62) | Male, 13 (54); Female, xi (46) | Due north/A | N/A | 34.9 ± one.v | 33.0 ± 1.3 | 0.46 | 0.10 | With Diabetes | Vegan | Meat nutrition | 20 weeks |
| Bloomer et al., 2015 (Traditional Daniel fast vs. Modified Daniel fast) | 2015 | United states of america | 33 ± 2 years (18–67 years) | Male, half dozen (17.i); Female, 29 (82.9) | N/A | N/A | 26.2 ± 1.3 (19–45) | 25.6 ± i.four (nineteen–45) | 0.04 | >0.05 | Without Diabetes | Vegan | Meat diet | three weeks | ||
| Ferdowsian et al., 2010 (low-fatty vegan nutrition vs. command diet) | 2010 | The states | 44.iv (21–65) | Male person, twenty (17.7); Female, 93 (82.3) | Due north/A | N/A | Northward/A | Due north/A | 0.017 | <0.0001 | With Diabetes | Vegan | Meat diet | 22 weeks | ||
| Hunt et al., 1998 (Lacto-ovo-vegetarian vs. non-vegetarian diet) | 1998 | United states | 33 ± seven (twenty–42) | Female, 21 women (100) | No, with the exception that ix used hormonal contraceptives | 23.5 ± two.8 (range: 19.0–29.0) | N/A | N/A | Without Diabetes | Lacto-ovo-vegetarian | Meat nutrition | eight weeks | ||||
| Lee et al., 2016 (Brown rice vegan diet vs. conventional diabetic diet) | 2016 | South Korea | 57.five ± vii.7 (32–seventy) | 58.three ± 7.0 (forty–69) | Male person, 6 (thirteen.0); Female, xl (87.0) | Male, 12 (25.v); Female, 35 (74.5) | DM (73.9); HPT (39.1); LIPID (fifty) | DM (76.6); HPT (46.8); LIPID (55.three) | 23.ix ± 3.4 | 23.i ± 2.4 | 0.042 | N/A | With Diabetes | Vegan | Meat diet | 12 weeks |
| Macknin et al., 2015 (Establish-based low fat diet vs. American Middle Association diets) | 2015 | USA | 15.0 (9.0–xviii.0) | fifteen.0 (nine.0–18.0) | Male, 5 (36); Female, 9 (64) | Male, 5 (36); Female, ix (64) | Due north/A | N/A | Overweight, four (29%); Obese, 10 (71%) | Overweight, two(xiv%); Obese, 12 (86%) | North/A | N/A | Without Diabetes | Vegan | Meat diet | 4 weeks |
| Mishra et al., 2013 (low-fat vegan nutrition vs. control diet) | 2013 | United states | 44.3 ± fifteen.3 | 46.1 ± thirteen.6 | Male, 32 (23); Female, 110 (77) | Male, xviii (12); Female person, 132 (88) | Due north/A | N/A | 34.7 ± 0.6 | 35.3 ± 0.seven | 0.09 | <0.001 | With Diabetes | Vegan | Meat diet | 18 weeks |
| Nicholson et al., 1999 (depression-fat Vegan nutrition vs. control diet) | 1999 | The states | Hateful 54.three | Male, (54.5); Female (45.v) | 81.80 | Northward/A | N/A | Due north/A | With Diabetes | Vegan | Meat nutrition | 12 weeks | ||||
| Prescott et al., 1987 (Lacto-ovo-vegetarian vs. non-vegetarian diet) | 1987 | Commonwealth of australia | 36.iv ± 2.4 | 34.0 ± 2.1 | Male, nine; Female, 16 | Male person, eleven; Female, xiv | North/A | Northward/A | 25.iii ± 0.ix | 25.5 ± 1.0 | N/A | North/A | Without Diabetes | Lacto-ovo-vegetarian | Meat diet | 12 weeks |
| Ramal et al., 2017 (High-fiber low-fat establish based nutrition vs. control nutrition) | 2017 | The states | 53.35 ± 6.74 | 52.93 ± 13.11 | Male, 4 (23.five); Female, 13 (76.5) | Male person, iii (20.0); Female person, 12 (80.0) | xv (88.2) | 13 (86.seven) | 31.81 ± 1.01 | 30.84 ± i.08 | Due north/A | N/A | With Diabetes | Vegan | Meat diet | 24 weeks |
| Rouse et al., 1986 (Lacto-ovo-vegetarian vs. non-vegetarian diet) | 1986 | Australia | Mean forty.1 | Male person (l); Female (fifty) | no | 23.7 | North/A | N/A | Without Diabetes | Lacto-ovo-vegetarian | Meat nutrition | 14 weeks | ||||
| Sciarrone et al., 1993 (Lacto-ovo-vegetarian vs. non-vegetarian diet) | 1993 | Australia | Mean 41 | Male (100) | no | 25.3 | N/A | N/A | Without Diabetes | Lacto-ovo-vegetarian | Meat diet | half-dozen weeks | ||||
| Toobert et al., 2000 (Prime time diet vs. Usual intendance nutrition) | 2000 | USA | 64 ± ten | 63 ± xi | Female, 25 (100) | ERT (35.seven); HPT (71.iv); LIPID (28.half-dozen) | ERT (45.5); HPT (81.8); LIPID (45.5) | 32 ± iv.2 | 32 ± five.5 | Northward/A | N/A | Without Diabetes | Lacto-ovo-vegetarian | Meat nutrition | 24 months | |
| Wright et al., 2017 (Low-fat plant-based nutrition vs. control diet) | 2017 | New Zealand | 56 ± 9.9 | 56 ± ix.5 | Male, eleven (33); Female, 22 (67) | Male, 15 (47); Female, 17 (53) | N/A | N/A | 34.5 ± 1.6 | 34.two ± 2.iii | N/A | N/A | With Diabetes | Vegan | Meat nutrition | 48 weeks |
iii.3. Effect of Vegetarian Diets on Systolic Blood Pressure Lowering and Its Subgroup Analysis
The outcome of vegetarian diets on lowering systolic claret pressure and subgroup analysis by diet subgroup, diabetes status, and country are shown in Tabular array 2. A significant reduction in systolic blood pressure was observed in those taking vegetarian diets every bit compared to those on a control diet (weighted hateful deviation (WMD = −2.655, 95% CI = −3.758, −1.553)) amidst all participants, regardless of historic period groups. Similar results were also obtained among developed participants (WMD = −two.509, 95% CI = −3.630, −1.388). In subgroup analysis, we observed that a vegan diet (WMD = −3.118, 95% CI = −four.540, −1.696) had a greater reduction in systolic claret pressure compared to a lacto-ovo-vegetarian nutrition (WMD = −1.752, 95% CI = −5.382, 1.878). Similarly, there was a greater reduction in systolic blood pressure amid participants without diabetes (WMD = −four.083, 95% CI = −7.684, −0.482) compared to those with diabetes (WMD = −1.625, 95% CI = −iii.106, −0.144).
Table ii
Weighted mean deviation and 95% conviction interval of claret pressure level by subgroup analysis.
| Variables | N | Weighted Mean Departure | 95% CI | I2 | p-Value | Forest Plot | |
|---|---|---|---|---|---|---|---|
| Systolic blood force per unit area | |||||||
| Overall systolic claret pressure (inclusive of children) | 16 | −ii.655 | (−3.758, −1.553) | 98.32 | <0.001 | Effigy S1 | |
| Overall systolic claret pressure (exclusive of children) | 15 | −2.509 | (−3.630, −1.388) | 98.42 | <0.001 | Figure S2 | |
| Diet subgroup | Vegan diet | 11 | −three.118 | (−four.540, −1.696) | 96.99 | <0.001 | Figure S3 |
| Lacto-ovo-vegetarian diet | 5 | −1.752 | (−5.382, 1.878) | 72.69 | 0.005 | ||
| Diabetes subgroup | Participants with diabetes | eight | −1.625 | (−iii.106, −0.144) | 96.84 | <0.001 | Effigy S4 |
| Participants without diabetes | 8 | −4.083 | (−7.684, −0.482) | 96.90 | <0.001 | ||
| Country | USA | 11 | −2.803 | (−four.037, −1.569) | 98.85 | <0.001 | Effigy S5 |
| Australia | iii | −2.075 | (−nine.859, 5.709) | 83.24 | 0.003 | ||
| New Zealand | 1 | −iv.000 | (−6.352, −1.648) | N.A | N.A | ||
| South Korea | 1 | i.000 | (−3.306, v.306) | N.A | N.A | ||
| Diastolic blood pressure | |||||||
| Overall diastolic blood force per unit area (inclusive of children) | sixteen | −i.687 | (−2.968, −0.407) | 99.35 | <0.001 | Effigy S6 | |
| Overall diastolic blood pressure (exclusive of children) | 15 | −one.654 | (−2.958, −0.351) | 99.39 | <0.001 | Figure S7 | |
| Diet subgroup | Vegan diet | 11 | −one.920 | (−iii.180, −0.661) | 97.80 | <0.001 | Figure S8 |
| Lacto-ovo-vegetarian diet | five | −0.000 | (0.000, 0.000) | 0.0 | 0.432 | ||
| Diabetes subgroup | Participants with diabetes | 8 | −1.838 | (−3.304, −0.373) | 98.46 | <0.001 | Figure S9 |
| Participants without diabetes | viii | −1.242 | (−2.551, 0.066) | 57.48 | 0.021 | ||
| Country | United states | 11 | −ii.179 | (−three.678, −0.680) | 99.57 | <0.001 | Figure S10 |
| Australia | 3 | −0.302 | (−2.912, two.308) | 0.0 | 0.468 | ||
| New Zealand | one | −ane.000 | (−2.176, 0.176) | Due north.A | N.A | ||
| South korea | 1 | 1.100 | (−1.501, 3.701) | Due north.A | Northward.A | ||
According to TSA, the cumulative Z-curve (bluish bend) shown in Figure two initially crossed the conventional boundary (Z-statistic above 1.96), based on the results of several trials [43,45,46,47,48,49,fifty,51,52,54,55,56]. However, it did not cross the conventional boundary when cumulating the results from the new trials [44,53,57] and demonstrated that vegetarian diets did not significantly reduce systolic blood pressure. However, the number of patients included in trial sequential assay did non exceed the required data size (that is, one thousand patients), indicating that the cumulative evidence for vegetarian diets not reducing systolic blood pressure remains inconclusive based on these 884 participants.
Trial sequential analysis on the issue of vegetarian diets vs. omnivorous nutrition on systolic blood pressure level reduction.
3.4. Result of Vegetarian Diets on Diastolic Blood Pressure level Lowering and Its Subgroup Analysis
The issue of vegetarian diets on diastolic blood pressure lowering and its subgroup analysis by diet subgroup, diabetes status, and country are shown in Table 2. A significant reduction in diastolic blood pressure was observed in those on vegetarian diets compared to those on a control nutrition (WMD = −i.687, 95% CI = −2.968, −0.407) among all participants, regardless of age group. A similar result was likewise obtained among adult participants (WMD = −i.654, 95% CI = −2.958, −0.351). In subgroup analysis, we observed that a vegan nutrition (WMD = −1.920, 95% CI = −three.180, −0.661) had a reduction in diastolic blood pressure, whereas a lacto-ovo-vegetarian diet brings no changes in terms of BP reduction at the end of the trial. (WMD = −0.000, 95% CI = −0.000, 0.000). Surprisingly, the reduction in diastolic blood pressure reduction was greater among participants with diabetes (WMD = −ane.838, 95% CI = −3.304, −0.373) as compared to those without diabetes (WMD = −one.242, 95% CI = −two.551, 0.066).
According to TSA, the cumulative Z-curve (bluish curve) shown in Figure iii initially crossed the conventional boundary (Z-statistic in a higher place ane.96) based on the results of several trials [43,45,46,47,48,49,50,51,52,54,55,56]. However, in one case once more it did not cantankerous the conventional boundary when cumulating the results from the new trials [44,53]. Afterward, i Z-curve crossed the conventional boundary again by cumulating the result from Wright et al. [57] and demonstrated that vegetarian diets are now associated with significant reduction in diastolic blood pressure. Withal, the number of patients included in trial sequential analysis did not exceed the required data size (that is, chiliad patients), indicating that the cumulative testify for whether a vegetarian diet can reduce diastolic blood force per unit area remains inconclusive based on these 884 participants.
Trial sequential assay on the effect of vegetarian diets vs. omnivorous diet on diastolic blood pressure reduction.
3.5. Chance of Bias within Studies
Risk of bias (Figures S11 and S12) was assessed under various categories such equally bias arising from the randomization process, bias due to deviations from intended interventions, bias due to missing result data, bias in measurement of the outcome, and bias in choice of the reported result. All included studies were randomized controlled trials, simply some studies gave cause for some concern of bias arising from the randomization process due to no information on how the randomization of sequence was conducted, how allocation sequences were concealed, and what baseline differences in that location were between intervention groups, suggesting a possible problem [46,47]. Studies with no data [51,54] and in which allocation sequences were not concealed [44] acquired some concern, even though the random component was used in the sequence generation procedure. All included studies [43,44,45,46,47,48,49,50,51,52,53,54,55,56,57] had unclear risk of bias to departure from intended intervention due to participants condign aware of intervention, and at that place was no information on whether carers and people delivering the interventions were aware of participants' assigned intervention during the trial. In addition, the diets taken by participants in both arms were either prepared by themselves with a guided cooking transmission [43,44,45,46,48,49,50,53,54,55,56,57], or recipes throughout the trials and diets taken by participants were prepared at the investigation sites in a total of 3 trials [47,51,52], thus these studies crusade some concern for bias due to divergence from intended intervention.
In the aspect of bias in outcomes measurement, the bulk of the trials are at depression risk of bias, except for one trial [43], which has allocation sequences that were not concealed. In the section for selection of the reported results, all studies had low risk of bias because the methods of measuring the outcome were appropriate and measurement of the outcome was the same between the intervention and control groups. For appraisement of bias in the option of the reported results, all studies displayed low risk of bias considering the data that produced this outcome were analyzed in accordance with a prespecified analysis plan, and there were no multiple outcome measurements for blood pressure within the outcome domain.
3.6. Class Assessment
A summary of the Course assessments of the overall certainty of the evidence for the effect of vegetarian diets on blood pressure lowering is demonstrated in Tabular array S3. The evidence was graded as very low for systolic and diastolic claret pressure owing to a downgrade for risk of bias and inconsistencies. A downgrade for chance of bias might exist because none of the included studies was ruled out for low gamble of bias in those five bias assessments domains. At that place was evidence of very serious inconsistencies according to the Itwo value, which indicated there are considerable proportions of variations due to interstudy differences.
4. Discussion
From the xv RCT that are included in our study, we noticed that the limerick of interventional nutrition in each study shows slight differences. For the Bernard report in 2009, the vegan diet with vitamin B12 supplementation consisted of vegetables, fruit, grains, and legumes, and was high in fiber and low in fat while the quantity, energy, and sugar intake were unrestricted [43]. The study from the same author in 2017 introduced the same diet composition as well [44]. Bloomer et al., 2015 used the "traditional" vegan-based Daniel fast diet that eliminates all processed foods and animate being products with no restrictions on the portion sizes of food [45]. Both the GEICO studies (Ferdowsian et al. and Mishra et al.) of South korea [46,fifty], Macknin et al. [49] and Nicholson et al. [51] followed a similar low-fat vegan nutrition as practiced in Bernard'south written report. The study from Hunt et al. was used a lacto-ovo-vegetarian diet, which consisted of legumes, whole-grain breadstuff and cereal products, and greater amounts of fruit and vegetables, and information technology had 25% less poly peptide, 12% less fatty, xvi% more carbohydrate, 21% more ascorbic acid, slightly less saturated fat and <100 mg/d less cholesterol than the nonvegetarian nutrition [47]. Prescott et al.'due south [52] interventional diet followed the nutrition of Seventh Twenty-four hours Adventist vegetarians studied in Rouse et al. [58]. In Ramal et al.'s study [53], the found-based diet was based on the thirty-Day Diabetes Miracle Cookbook [59] and was modified to conform the ethnic groups. Both Australian trials, namely Rouse et al. [54] and Sciarrone et al. [55] required those with lacto-ovo-vegetarian diet to maintain the intake of salt, eggs, and milk products with their routine nutrition patterns, with the menu and guidelines modified from the NUTRIVIEW plan version 1.i. For Toobert et al.'s study [56], subjects were required to attach to Reversal Diet guidelines [60], which contain no fauna products other than egg whites, and non-fat yogurt with no added oils or other full-bodied fats. Lastly the New Zealand study [57] on interventional diet was based on the whole nutrient plant-based (WFPB) diet by the McDougall Program, which is also low in fat [61].
This meta-assay revealed that a vegetarian dietary pattern significantly reduced systolic and diastolic blood pressure level by WMD −2.655 and WMD −ane.687, respectively. In general, this study yielded a similar finding to a previous meta-analysis of vii randomized controlled trials and thirty-two observational studies, which showed that the WMD in consumption of vegetarian diets versus omnivorous diet was systolic blood pressure of −4.8 mmHg in controlled trials and −6.ix mmHg in observational studies [24], while for diastolic blood pressure, the differences were −2.two mmHg in controlled trials and −four.seven mmHg in observational studies [24]. The like design in reduction of blood pressure in participants that received vegetarian diets as observed in the electric current study and previous study are definitely important to people with underlying diseases whom are currently not on a regular vegetarian nutrition, because the previous study indicated that by lowering i mmHg of systolic blood pressure it could reduce the incidence of coronary heart illness by 13.5 events, stroke past 12.1 events, and center failure by xx.three events per 100,000 person-years [62]. Moreover when systolic blood pressure level was lowered past ii mmHg, it essentially reduced the hazard of cardiovascular diseases (27 events for coronary heart illness; 24.2 events for stroke; and 40.6 events for heart failure per 100,000 person-years) [62]. One of the possible mechanisms associated with the reduction in blood force per unit area seen with a vegetarian nutrition could exist overwhelmingly due to its lowering effect of total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and non-high-density lipoprotein cholesterol [63]. This is because the vegetarian nutrition is high in fiber, and omega-6 polyunsaturated fatty acids but depression in cholesterol, total fat and saturated fatty acids as compared with omnivorous diet [64]. With a lower cholesterol level, this further helps to regulate the blood pressure [65]. The vegetarian diet is likewise rich in phytochemicals and antioxidants [64]. Previous studies have demonstrated that diets rich in fruits, vegetables, and whole grains, which atomic number 82 to an increase in blood antioxidant capacity, can reduce systolic and diastolic blood pressure in both hypertensive and normotensive patients [66,67].
Among the various vegetarian diets, there was a difference result between the vegan and lacto-ovo-vegetarian diets. Greater reduction of BP was observed in the vegan nutrition. In that location was a greater BP reduction for the vegan nutrition (WMD = −3.118, 95% CI = −4.540, −1.696) besides as greater reduction in systolic blood pressure in the lacto-ovo-vegetarian diet (WMD = −1.752, 95% CI = −5.382, 1.878) compared with the omnivorous diet. This tin can be explained by the fact that regular consumption of meat, especially blood-red meat, likewise increases the hazard of falling sick because the processed derivatives in meat products are an associated gene for hypertension [68,69,lxx]. Besides, vegetarians have a significantly lower ischemic center affliction mortality (29%) [71]. These results are in accord with a large cohort study conducted in America and Canada which indicated that the odds ratio for developing hypertension was bottom for vegetarian diets compared with an omnivorous diet: 0.37 (95% CI 0.19, 0.74) for vegans, 0.57 (95% CI 0.36, 0.92) for lacto-ovo-vegetarians and 0.92 (95% CI 0.50, one.70) for partial vegetarians [72].
This finding suggested that dietary patterns based solely on plant sources are more effective in reducing claret pressure than other types of vegetarian diet which notwithstanding include brute products or byproducts, such every bit eggs and dairy products, for example, in the lacto-ovo-vegetarian diet. This result is supported by previous studies in which high consumption of fruit and vegetables are associated with reduction of claret pressure when compared with those with a college intake of dairy products [73,74,75]. One of the possible explanations for such an observation could be the higher content of saturated fat acids in dairy products that touch the blood lipid contour by increasing depression-density lipoprotein cholesterol and promoting atherosclerosis that might take contributed to higher blood pressure [76]. However, it should be noted that information technology is hard to compare the effect of different types of the vegetarian diet in this study due to the different sample characteristics of each of these studies, therefore nosotros should interpret the benign effect of vegetarian nutrition on blood pressure level with great caution.
Even though vegetarian diets significantly improved both systolic and diastolic claret pressure, higher systolic claret pressure level reduction was observed among subjects without diabetes (WMD = −4.083, 95% CI = −7.684, −0.482) compared to those with diabetes (WMD = −ane.625, 95% CI = −iii.106, −0.144). An opposite trend was observed with diastolic blood pressure in which college diastolic blood pressure reduction was observed among subjects with diabetes (WMD = −1.838, 95% CI = −iii.304, −0.373) compared to those without diabetes (WMD = −1.242, 95% CI = −2.551, 0.066). It could be because the mean age of the diabetic group (54.nine years old) was much older than the nondiabetic grouping (xl.ix years onetime), and thus the diastolic BP reduction was non much observed amidst the younger nondiabetic group.
Therefore, vegetarian diets accept the potential to be recommended to those with underlying disease as well as the full general population, in the hope that, through this nonpharmacological diet method, uncontrolled hypertension could be reduced, which would result in a meaningful decrease in the run a risk of developing cardiovascular diseases as well as other morbidities and mortality and lessen the excessive demand on healthcare.
We also performed the meta-analysis with trial sequential analysis to estimate the effect vegetarian diet had on BP reduction. To provide insight into the ability of sample size to conclude the findings, the number of patients included in trial sequential analysis did not exceed the required data size (that is, one thousand patients). Similar findings are applied to both systolic and diastolic blood force per unit area as the number of patients included in trial sequential analysis also similarly did not exceed the required data size (that is, g patients). This indicated the cumulative bear witness on whether vegetarian diets can reduce systolic and diastolic blood pressure remains inconclusive based on these 884 participants.
Limitations and Futurity Research Recommendation
The electric current meta-assay has several limitations. Firstly, there was high heterogeneity among the controlled trials included in the analysis. The heterogeneities across studies could be due to participant characteristics, such as some of the trials involved participants with lifestyle restriction practices including limiting booze, common salt, fatty food, caffeine intake, and/or cigarette smoking while others did non. These are confounding factors to blood pressure control, thus, information technology may affect the findings of the written report.
Secondly, this study only includes dietary patterns, instead of isolated nutrients. There was a lack of information on the diet value of various diet regiments consumed by participants in those trials in both the interventional and command arms. Hence, it may cause a plausible application of the results to both general and clinical populations. Only with the availability of the nutritional value of these diets, could nosotros then give recommendations regarding the specific quantities of these foods that should be consumed for the best positive effect. It is important to know energy intake could exist an important factor influencing trunk weight and blood pressure reduction; withal, there was also a lack of information on comparisons of changes from baseline to concluding values for energy intake and body weight between vegetarian diets compared with control diets. Therefore, nosotros could non entangle energy intake on blood pressure lowering in the current study.
Thirdly, the included studies were mainly conducted in the United states and other Western countries (Australia and New Zealand). Hence, information technology cannot be generalized to other populations. Additionally, heavy metals tin can be found both in animate being-derived food or plant-based nutrient. However, sometimes it may be higher in the latter one every bit they tin be easily contaminated with heavy metals such every bit arsenic, cadmium and pb, from the h2o, air, and soil as they abound [77,78,79,fourscore]. These heavy metals accept been institute to inactivate catechol-O-methyltransferase (COMT), which increases serum and urinary epinephrine, norepinephrine, and dopamine [81]. This resulted in hormone imbalances, vasoconstriction, and afflicted renal tubular role, which somewhen leads to hypertension [82].
Fourthly, as mentioned previously, the sample size gathered from all clinical trials done in the past has non yet reached the required sample size for cartoon a conclusive statement. Therefore, we suggest that, in future, larger randomized clinical trials aimed at examining the upshot of the vegetarian nutrition on blood pressure be conducted, paying attention to publication bias. Furthermore, the number of studies is minor and any derived conclusions should be fabricated with caution.
v. Conclusions
However these limitations, this study suggests that, show from clinical trials has shown that vegetarian diets, peculiarly vegan diets, reduce claret pressure when compared with omnivorous diets, suggesting that they may be crucial in the master prevention and overall management of hypertension.
Acknowledgments
We would like to thank the Director General of Health Malaysia for his permission to publish this article.
Supplementary Materials
The following are bachelor online at https://www.mdpi.com/2072-6643/12/vi/1604/s1, Figure S1. Forest plot for overall systolic blood pressure (inclusive of children). Figure S2. Forest plot for overall systolic blood pressure level (exclusive of children). Figure S3. Forest plot for overall systolic blood pressure level (nutrition subgroup). Figure S4. Woods plot for overall systolic claret pressure level (diabetes subgroup). Figure S5. Forest plot for overall systolic blood pressure level (country subgroup). Figure S6. Wood plot for overall diastolic blood pressure (inclusive of children). Effigy S7. Forest plot for overall diastolic claret pressure (exclusive of children). Figure S8. Woods plot for overall diastolic blood pressure (nutrition subgroup). Effigy S9. Forest plot for overall diastolic blood pressure (diabetes subgroup). Effigy S10. Wood plot for overall diastolic blood pressure (country subgroup). Effigy S11. Risk of bias graph shows review authors' judgements about each risk of bias items presented equally percentages across all included studies. Figure S12. Risk of bias summary shows review authors' judgements about each risk of bias items for each included studies. Table S1. Search terms used for final search on six January 2020. Table S2. Boosted information on characteristics of trials. Tabular array S3. Form quality assessment for the written report findings was summarised equally followed.
Author Contributions
Conceptualization, K.W.50., H.C.L. and F.K.H.; methodology, K.W.L., H.C.Fifty., Southward.M.C., N.M.D. and F.One thousand.H.; software, K.W.L. and H.C.Fifty.; validation, S.G.C., N.K.D. and F.K.H.; formal analysis, Chiliad.W.50. and H.C.Fifty.; investigation, S.M.C., Northward.Chiliad.D. and F.K.H.; resources, S.K.C., N.K.D. and F.M.H.; data curation, S.M.C., N.K.D. and F.M.H.; writing—original draft preparation, G.Westward.L. and H.C.L.; writing—review and editing, Southward.Yard.C., N.K.D. and F.G.H.; visualization, G.Westward.50. and H.C.L.; supervision, H.C.L.; project administration, S.M.C.; funding conquering, Not applicative. All authors have read and agreed to the published version of the manuscript.
Funding
This enquiry received no external funding.
Conflicts of Interest
The authors declare that they have no competing interests.
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