The Effect of Plant-Based Nutrition Diets: History
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Subjects: Nutrition & Dietetics
Contributor:
Corina Zugravu

Diet is an important tool in managing dyslipidemic disorders, thus contributing to the prophylaxis of cardiovascular morbidity. Plant based diets are promising tools in the management of cardiovascular diseases and they should be taken intro consideration by all medical practitioners

  • plant-based
  • cardiovascular disease
  • vegan
  • health promotion
  • dyslipemia
  • triglycerides
  • cholesterol

1. Introduction

Cardiovascular diseases are important causes of morbidity and mortality in the contemporary world. Primary and secondary prophylaxes are important targets, but measures are relatively difficult to be applied in current practice, due to the multifactorial etiology of this pathology. Mostly all prophylactic interventions also aim to improve the lipid profile, to reduce the level of lipoproteins that contain a high quantity of cholesterol (primarily LDL-C), and to increase the number of particles involved in the reverse transport of cholesterol, HDL-C. Oxidized LDL-C is absorbed by the subendothelial macrophages, after which the macrophages transform into foam cells and promote the expression of pro-inflammatory genes (e.g., nuclear factor kappa B-NFkB), initiating the inflammatory response. The lipid striae are formed initially, then, through structural and functional changes of the middle vascular tunic, the atheroma plaque is built, the vessel loses its normal secretory properties (e.g., secretion of vasodilators, such as nitric oxide), suppleness, anticoagulant, and fibrinolytic properties. This creates the pathophysiological substrate for hypertension and thrombosis.
TGs are found in large quantities in chylomicrons (in the postprandial phase) and in very low-density lipoprotein cholesterol (VLDL-C) particles (in the interprandial phase); these plasma transporters are susceptible to the action of lipoprotein lipase, which cleaves TGs into fatty acids and glycerol, lipid components that can be taken up by cells, including the vascular endothelial cell and that can initiate inflammatory processes in the vascular intima. Although TGs are not components of the atheroma plaque, elevated levels are an indirect marker of high VLDL-C levels [1]. Both TG and TC levels are influenced by intake, especially the intake of carbohydrates and lipids in the diet, as well as alcohol consumption. Clinical studies have shown that improving the lipid profile has yielded results in terms of cardiovascular risk. Modifying the diet model is, in theory, a method available to every individual, correctly guided by specialists. Therefore, the approach to dyslipidemias can be successful through dietary changes, reduced hypertriglyceridemia and hypercholesterolemia being reported in many scientific studies. Moreover, current prevention guidelines state that the most important prevention measures are adherence to a healthy lifestyle, in which diet plays a central role [2].
Among the diets most often recommended for normalizing the plasma lipid profile, the most effective have been those based on plants. In these diets, most calories come from foods of plant origin, food of animal origin being present in small quantities. Lipid intake is usually variable but always is made mostly of unsaturated lipids, which largely replace saturated lipids, very abundant in the diet of the modern human. The presence of soluble fiber, antioxidant minerals, vitamins, phytonutrients, the low glycemic load, and the lack of cholesterol are some of the attributes of these diets. In addition, studies have shown that this kind of diet is associated with a lower incidence of high blood pressure and a lower BMI [3][4][5][6][7][8][9], factors involved in the prophylaxis of cardiovascular diseases. A classic example of a plant-based diet is the Mediterranean diet, even if the model used today is slightly different from the original type, much richer in vegetable oils [10].
In the last decade, more and more place was gained by diets mostly or completely based on plants (vegan, plant-based), in which foods of animal origin are completely excluded and all calories come from plant foods. This diet is based on cereals, legumes, pulses, including soy, which are completed with significant amounts of vegetables and fruits. Most dietary lipids are components of these food groups and are supplemented by others from oilseeds and oily fruits (olives, almonds, cashews, etc.). The addition of commercial oils is optional [11]. The reported action of the plant-based diet on the lipid profile has been favorable in many studies [12][13][14][15][16]. Of course, controlled clinical trials would be necessary to assess the direct effects on the associated pathology, but such studies are difficult, if not impossible to be performed when it comes to food and diets [17]. In addition, the diet effects are not always enough and must be supplemented by appropriate medication, taking into account that the lipid profile has a complex determinism, including a variety of gene polymorphisms [18][19][20][21][22]. Physical exertion also alters the transport of cholesterol between the central metabolic compartment (liver), physiological storage tissue (adipose tissue), and other peripheral tissues of the body, including vascular wall structures, thus reducing direct transport by reducing LDL-C and promoting reverse transport by increasing HDL-C [17].

2. Current Insight on  A Plant-Based Diet

The group included 20 women and 18 men. The average age was 36 years. The youngest respondent was 21 years old and the oldest 65. The level of education was high, with 27 being college graduates, 6 had postgraduate studies, and 5 had high school education. The most common duration of plant-based adherence was 2 years (in 29% of members).
All participants were never smokers. Alcohol consumption was scarce, all of the respondents stating that they drink 1–2 glasses of alcoholic beverages once a month or less. In the qualitative evaluation of food intake, all participants reported following a whole food plant-based diet, which included less than one portion per week of vegan fast food (mock meat, mock cheese, sweets, etc.).
The whole group declared themselves physically active, with at least half an hour of strenuous physical activity per day. When asked about weight loss, 14 persons answered that they had lost weight since the adoption of the plant-based diet, which was not confirmed by the comparison of BMI, showing that only seven people lost weight since the adoption of this particular diet.
Regarding the presence of associated chronic diseases, five people were diagnosed with allergies during their lifetime and two with immunological disorders (rheumatoid arthritis). All of them had extensive medical documents to confirm these conditions. No cardiovascular disease could be documented in any of the participants. Out of the whole group, three people were currently under treatment with hypocholesterolemic medication (statins). In all of them, the onset of the treatment was subsequent to the beginning of the vegan diet.
Along with lipid values, documents sent by participants included other values of blood parameters (glycaemia, proteinemia, calcemia, etc.) that have been analyzed and no statistical differences were noticed for any of them when comparing values from the pre-vegan period with the vegan one. Table 1 shows mean values of BMI and circulating lipids, before and after adopting a vegan diet, in women and men (t-test was applied for statistical significance evaluation).
Table 1. BMI and lipid profile before (1) and after (2) dieting.
Variable Men (Mean Value) Women (Mean Value)
BMI 1 (kg/m2) 22.3 23.0
BMI 2 (kg/m2) 21.2 22.2
p 0.001 0.006
TG 1 (mg/dL) 117.6 117.9
TG 2 (mg/dL) 104.3 102.6
p 0.003 0.005
TC 1(mg/dL) 0.186.5 203.4
TC 2 (mg/dL) 152.9 168.3
p 0.000 0.000
HDL-C 1(mg/dL) 45.0 48.2
HDL-C 2(mg/dL) 43.7 47.4
  0.338 0.530
LDL-C 1 (mg/dL) 133.3 143.5
LDL-C 2 (mg/dL) 99.0 108.9
p 0.000 0.000
TC/HDL-C 1 4.1 4.2
TC/HDL-C 2 3.5 3.5
p 0.000 0.000
BMI—body mass index, TG—triglycerides, TC—total cholesterol, HDL-C—high-density lipoprotein cholesterol, LDL-C—low-density lipoprotein cholesterol, TC/HDL-C—total cholesterol to high-density lipoprotein cholesterol ratio.
 
Decreases in the mean values can be observed in all parameters. Results were in all cases statistically significant, with the exception of HDL-C. Indeed, HDL-C shows a variation found in other studies performed on vegans and vegetarians (Table 2), with 82.4% of those with low values (below 40 mg/dL) failing to reach higher normal and protective categories.
Table 2. Percent of persons (%) “migrating” between categories of cardiovascular risk related to the HDL-C.
  HDL-C 2 Category
Normal Low Protective
HDL-C 1 category normal 17.6% 82.4% -
low 93.8% 6.2% -
protective 50.0% - 50.0%
HDL-C 1—high-density lipoprotein cholesterol before plant-based diet; HDL-C 2—high-density lipoprotein cholesterol after plant-based diet.
 
Changes in the TG categories are presented in Table 3. 75% of people with high TG values managed to normalize them. Regarding TC, data are presented in Table 4. All borderline values decreased within normal limits and only 30% of the increased values did not change.
Table 3. Percent of persons (%) “migrating” between categories of cardiovascular risk related to TGs.
  TG 2 Category
Normal Borderline Elevated
TG 1 category normal 100% -
borderline elevated 75% 25%
TG 1—triglycerides before plant-based diet; TG 2—triglycerides after plant-based diet.
 
Table 4. Percent of persons (%) “migrating” from a category to another of TC after becoming plant-based, where TC 1 are % before plant-based and TC 2 after.
  TC 2 Category
Optimal Borderline Elevated Elevated
TC 1 category optimal 100% - -
borderline elevated 100% - -
elevated 30% 40% 30%
TC 1—total cholesterol before plant-based diet; TC 2—total cholesterol after plant-based diet.
 
Of all the lipid markers, LDL-C was the most influenced. Only 9.1% of those with optimal showed an increase (up to the elevated borderline category) and 22.2% of those with high values remained in the same category (Table 5).
Table 5. Percent of persons (%) “migrating” from a category to another of LDL-C after becoming plant-based, where LDL-C 1 is % before plant-based and LDL-C 2 after.
  LDL-C 2 Category
Optimal Borderline Optimal Borderline Elevated Elevated Very Elevated
LDL-C 1 category optimal 100% - - - -
borderline optimal 83.8% 16.2% - - -
borderline elevated 72.7% 18.2% - 9.1% -
elevated - 66.7% 33.3% - -
very elevated - - 66.7% 11.1% 22.2%
LDL-C 1—low-density lipoprotein cholesterol before plant-based diet; LDL-C 2—low-density lipoprotein cholesterol after plant-based.
 
Finally, from the analysis of the TC/HDL-C ratio, “migrations” could be observed towards higher-risk categories in only 12.5% of participants, the rest remained in the initial category or decreased their ratio, which led to a decreased potential risk of cardiovascular disease (Table 6).
Table 6. Percent of persons (%) “migrating” from a category to another of TC/HDL-C ratio after becoming plant-based, where TC/HDL-C 1 is % before plant-based, and TC/HDL-C 2 after.
  TC/HDL-C 2
Ideal Optimum Increased
TC/HDL-C 1 Ideal 100% - -
Optimum 62.5% 25.0% 12.5%
increased 7.1% 78.6% 14.3%
TC/HDL-C 1—total cholesterol/high-density lipoprotein cholesterol before plant-based diet; TC/HDL-C 2—total cholesterol/high-density lipoprotein cholesterol after plant-based diet.
 
In the next step, a Wilcoxon signed-rank test was applied for circulating lipid values, considered as categorical (ordinal) values as described in the methods section, before and after becoming plant-based. In all cases results from t-tests: for TC (Z = −3.35; p = 0.001), LDL-C (Z = −4.47; p = 0.000), and TC/HDL-C (Z = 4.04; p = 0.000). The only non-significant change was of HDL-C (Z = 3.78; p = 0.705). These changes converged for a positive evolution of the lipid profile, with subjects expressing a shift from a higher category of risk to a lower one.
Regarding BMI, several changes were noted: 13% (n = 3) of normal-weight individuals (n = 23) became underweight, 20% (n = 2) of overweight (n = 10) became normal weighted, and all obese (n = 2) became overweight. As mentioned above (Table 1), the mean differences in BMI both in men and in women were statistically significant.
The Wilcoxon signed-rank test applied to the BMI changes showed a significant difference (Z = 2.64; p = 0.008) after the introduction of the plant-based diet.
Additionally, in order to outline the possible reciprocal influences between variables, the Pearson correlation test was applied. This test highlighted a significant positive correlation only between the BMI variation and the TC variation (correlation coefficient: 0.34, p = 0.045). The statistical significance is maintained even in partial correlation, with age as a covariate The duration of the plant-based regimen did not correlate with any of the above variables.

3. Summary

Although dyslipidemias are only a surrogate marker for cardiovascular morbidity and the actions by which the plant-based diet can influence cardiovascular diseases are multiple and positive. After a minimum of one year of plant-based regimen, low in any processed vegetarian foods, nonsmokers had favorable effects in terms of markers such as TG, TC, and LDL-C. However, such diets had limited benefits in familial hypercholesterolemia, which requires specialized investigations and drug treatment.

This entry is adapted from the peer-reviewed paper 10.3390/su14021008

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