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Dyslipidemia is a primary risk factor for cardiovascular disease, peripheral vascular disease, and stroke. Current guidelines recommend diet as first-line therapy for patients with elevated plasma cholesterol concentrations. However, what constitutes an optimal dietary regimen remains a matter of controversy. Large prospective trials have demonstrated that populations following plant-based diets, particularly vegetarian and vegan diets, are at lower risk for ischemic heart disease mortality. The investigators therefore reviewed the published scientific research to determine the effectiveness of plant-based diets in modifying plasma lipid concentrations. Twenty-seven randomized controlled and observational trials were included. Of the 4 types of plant-based diets considered, interventions testing a combination diet (a vegetarian or vegan diet combined with nuts, soy, and/or fiber) demonstrated the greatest effects (up to 35% plasma low-density lipoprotein cholesterol reduction), followed by vegan and ovolactovegetarian diets. Interventions allowing small amounts of lean meat demonstrated less dramatic reductions in total cholesterol and low-density lipoprotein levels. In conclusion, plant-based dietary interventions are effective in lowering plasma cholesterol concentrations.
Dyslipidemia is a primary risk factor for heart disease, peripheral vascular disease, and stroke.
suggesting that factors other than genetics are involved in hyperlipidemia. A summary analysis of 5 observational studies demonstrated that populations consuming plant-based (especially vegetarian and vegan) diets typically have significantly lower blood concentrations of TC and LDL cholesterol and correspondingly lower rates of coronary artery disease compared to the general population.
In 2004, the NCEP and the third report of the Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults recommended the Therapeutic Lifestyle Changes plan, which calls for limiting total and saturated fats and dietary cholesterol and including plant sterols, viscous fibers, soy protein, and nuts, as the initial intervention for cholesterol reduction.
We reviewed the published scientific research to ascertain the extent to which a plant-based diet alters plasma and serum lipids, as well as potential mechanisms for these actions.
We conducted a search of the Medline and Cochrane Collaboration databases with the terms “cholesterol,” “total cholesterol,” “low density lipoprotein,” and “lipids” cross-referenced with “vegetarian,” “low-fat vegetarian,” “vegetarianism,” “plant-based diet,” and “plant diet” for reports published from 1966 to February 2009. We also used bibliographies and studies suggested by search engines to further increase the range of data collected. Reports published in languages other than English were reviewed if English translations were available. Studies were included if (1) the reported studies included human volunteers of any age, gender, or health status; (2) the number of participants as well as their ages and clinical status were delineated; (3) the duration and type of trial were reported; (4) the trials involved plant-based diets (diets with no, or almost no, meat products); (5) for longitudinal studies or clinical trials, lipid values, including at least TC and LDL cholesterol concentrations, were drawn before and after the study intervals; (6) the trials included adequate control groups; and (7) studies included information about the statistical significance of such findings. Observational and intervention studies were included. One investigators (B.M.K.) conducted the review, and this process was evaluated and confirmed by the other 2 investigators. Disagreements were resolved by consensus.
We found 7,261 studies, of which 7,096 were excluded on the basis of screening using general criteria. The remaining 165 abstracts were reviewed, and full reports were evaluated. Of these, 27 met all inclusion criteria. Reports were excluded because they did not report the effects of diet on cholesterol, did not include LDL values, did not use plant-based diets, were not in English, or did not report human studies (Figure 1).
Four primary dietary interventions were identified: vegan (allowing no animal products), ovolactovegetarian (allowing eggs and dairy products), primary plant (similar to the ovolactovegetarian diet but allowing small amounts of lean meat), and combination (a vegetarian or vegan diet combined with nuts, soy, and/or fiber).
Of the 13 observational studies that met the inclusion criteria, 10 were cross-sectional studies and 3 were case-control studies. Reviewed in Figure 2, Figure 3 and listed Table 1, these trials evaluated 4,772 participants from 6 countries with populations of varied age ranges, gender representation, and racial and ethnic compositions.
Table 1Observational studies evaluating the effects of diet on lipids
In studies that evaluated the effects of different plant-based diets (i.e., ovolactovegetarian, lactovegetarian, and vegan), populations following vegan diets had the lowest cholesterol concentrations.
studied Seventh-Day Adventist vegetarians and nonvegetarians in New Zealand and reported significant differences in saturated fat (15.4% vs 10.4% of energy) and cholesterol intake (279 vs 133 mg/day) but found no significant differences in lipid parameters.
Randomized controlled trials
Fourteen randomized controlled trials met the inclusion criteria. These included 2 studies evaluating primary-plant diets, 5 studies evaluating vegetarian diets, 3 studies evaluating vegan diets, and 4 studies evaluating combination diets. Summarized in Figure 3, Figure 4, Figure 5 and listed in Table 2, these trials included 1,939 participants from 6 different countries.
Table 2Randomized controlled trials evaluating the effects of diet on lipids
compared a low-fat NCEP Step I diet and a “low-fat plus” diet in adults with hypercholesterolemia recruited from newspaper advertisements and brochures mailed to previous study participants and Stanford University employees. The diets were identical in total fat, saturated fat, protein, carbohydrate, and cholesterol contents, but the low-fat plus diet included “considerably more vegetables, legumes, and whole grains” and <1 serving of meat or eggs per week. All food was provided except for 1 “free-choice” meal per week. Lipid concentrations of participants assigned to the 2 groups decreased significantly, although the results were more dramatic in those in the low-fat plus arm.
tested the effects of macronutrient content in a racially diverse group of participants with hypertension and prehypertension who were not taking medications that affected lipids or blood pressure. Participants were primarily recruited through mass mailings and advertisements in Baltimore, Maryland, and Boston, Massachusetts. In an attempt to determine the best macronutrient combination, the investigators substituted either protein or monounsaturated fat for carbohydrate in a diet patterned after that used in the Dietary Approaches to Stop Hypertension (DASH) study. Protein (of which 2/3 came from plants) accounted for 25% of energy in the high-protein diet, and fat (55% monounsaturated) accounted for 37% of energy of the high-fat diet. Participants were provided with all food. Compared to participants assigned to the low-fat diet, participants assigned to the high-protein diet experienced significant decreases in TC, LDL cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides, and non-HDL cholesterol. Participants assigned to the monounsaturated fat diet experienced decreases in TC, triglycerides, and non-HDL cholesterol and increases in HDL cholesterol compared to participants assigned to the low-fat diet.
Of 19 randomized controlled studies, 8 tested the effect of vegetarian diets on plasma lipids. Of these, 5 used ovolactovegetarian diets and 3 used low-fat vegan diets.
tested the lipid-lowering effects of a lactovegetarian diet in healthy, nonsmoking physicians and medical students recruited from the Chicago area. Participants were randomly assigned to a low–saturated fat vegetarian diet or a “typical American diet.” While consuming the vegetarian diet, participants reported consuming 30% fewer calories, with 11% of energy from protein, 20% from fat, and 69% from carbohydrate. Participants consuming the vegetarian diet experienced significant decreases in TC and LDL cholesterol.
studied the effects of an ovolactovegetarian diet, a lean-meat diet, and a typical Australian diet in participants with moderate cholesterol levels recruited from a “non-profit fitness institute” in the Adelaide, Australia, area. Participants eating the lean-meat and ovolactovegetarian diets reduced TC and LDL cholesterol concentrations and increased triglycerides, with no change in HDL cholesterol. While consuming the ovolactovegetarian diet, participants' TC and LDL cholesterol concentrations decreased significantly more than while consuming the lean-meat or Australian diet.
evaluated whether a low-fat vegetarian diet, in addition to lifestyle modification (smoking cessation, exercise, and stress management), could improve plasma cholesterol concentrations and reverse atherosclerosis. Participants with diagnosed coronary artery disease and not taking lipid-lowering drugs were recruited from 2 San Francisco–area hospitals. After 1 year, the intervention group had lower TC and LDL cholesterol concentrations compared to controls. Triglycerides and HDL cholesterol concentrations remained unchanged in the 2 groups. Lipid values did not change significantly in the control group. Atherosclerotic stenosis decreased by 2.2% in mean diameter in the intervention group, while lesions worsened by 3.4% in the control group.
After an additional 4 years, with 35 of the original participants,
the intervention group continued to maintain decreased TC and LDL cholesterol values without medication. The investigators noted the addition of statins in 9 of the control subjects (60%), compared to none in the intervention group. Atherosclerotic stenosis decreased by 3.1% in mean diameter in the intervention group, whereas lesions worsened by 11.8% in the control group (p = 0.001). Control-group participants experienced twice as many cardiac events compared to intervention-group participants.
Assessing mineral absorption and lipids, Hunt et al
recruited premenopausal women with no apparent underlying diseases through public advertisements in North Dakota. Participants were assigned, in random order, to a nonvegetarian or an ovolactovegetarian diet. All foods were provided. The ovolactovegetarian diet included more whole grains, legumes, fruits, vegetables, nuts, and seeds, with 25% less protein, 12% less fat, and 16% more carbohydrate, as well as 96 mg/day less cholesterol and 24 g/day more fiber. While consuming the intervention diet, the women experienced decreased TC, LDL cholesterol, and HDL cholesterol. Apolipoprotein (apo) A-1, apo B, and lipoprotein(a) were also significantly decreased.
evaluated the effects a very high fiber vegan diet compared to a control diet (usual diet) on plasma lipid concentrations in healthy volunteers recruited from the University of Toronto graduate student population and the university and hospital staff population. While following the vegan diet, participants had decreases in TC, LDL cholesterol, and triglyceride concentrations. Significant reductions were also noted in the TC/HDL cholesterol ratio, the LDL cholesterol/HDL cholesterol ratio, and the apo B/apo A-1 ratio. Reductions in TC were 34% to 49% greater than expected by differences in dietary fat and cholesterol alone.
studied the effects of a vegan diet consisting of grains, vegetables, legumes, and fruits in a population of premenopausal women with normal plasma lipid concentrations. Participants were recruited by newspaper advertisements and brochures mailed to physicians in the Washington, District of Columbia, area. Participants were asked either to continue their customary diets and to take a placebo pill or to begin a low-fat (10% of energy from fat) vegan diet, each for 2 menstrual cycles, in random order. Food was not provided, but participants received weekly group nutrition instruction. While consuming the vegan diet, participants' TC, LDL cholesterol, and HDL cholesterol concentrations decreased and their triglycerides increased significantly more than while consuming the control diet.
evaluated the effects of diet in 99 volunteers with type 2 diabetes recruited by advertisements in Washington-area newspapers. Participants were randomized to a low-fat, low–glycemic index vegan diet, or control diet based on 2003 American Diabetes Association guidelines.
At the end of the trial, more participants following the vegan diet decreased their cholesterol and diabetes medications, compared to participants following American Diabetes Association guidelines. After controlling for changes in lipid-lowering medications, participants assigned to the vegan diet experienced greater decreases in TC and LDL cholesterol values compared to participants assigned to the American Diabetes Association diet.
Certain foods appear to have specific lipid-lowering properties: plant sterols, viscous fibers, soy proteins, and almonds may all contribute to lowering cholesterol. Accordingly, Jenkins et al
evaluated the effects of a vegan dietary “portfolio” including plant sterols 1.2 g/1,000 kcal, soy protein 16.2 g/1,000 kcal, viscous fiber 8.3 g/1,000 kcal, and almonds 16.6 g/1,000 kcal. Participants were recruited from patients attending the Risk Factor Modification Center at St. Michael's Hospital in Toronto, Ontario, Canada, and from newspaper advertisements and asked to follow a low-fat diet for 1 month. Participants were then randomized to either the portfolio diet or an NCEP Step II ovolactovegetarian diet. Participants assigned to the portfolio diet experienced greater decreases in TC, LDL cholesterol, apo B, TC/HDL cholesterol ratio, LDL cholesterol/HDL cholesterol ratio, and apo B/apo A-1 ratio compared to participants assigned to the control diet.
In a population similar to the previous study, Jenkins et al
directly compared a vegetarian portfolio diet (plant sterols 1.0 g/1,000 kcal, soy protein 21.4 g/1,000 kcal, viscous fiber 9.8 g/1,000 kcal, and almonds 14 g/1,000 kcal) to a low-fat diet plus placebo (control group) and a low-fat diet plus lovastatin. Compared to controls, participants assigned to the lovastatin and portfolio groups significantly reduced TC and LDL cholesterol concentrations. The lovastatin and portfolio diet groups significantly reduced C-reactive protein levels, TC/HDL cholesterol ratios, HDL cholesterol/LDL cholesterol ratios, apo B values, and apo B/apo A-1 ratios. There were no differences between the lovastatin and portfolio diet groups in any changes in plasma lipid concentrations.
compared 3 dietary interventions: a low-fat NCEP Step II diet, lovastatin 20 mg plus a low-fat NCEP Step II diet, and the portfolio diet (plant sterols 1.0 g/1,000 kcal, soy protein 21.4 g/1,000 kcal, viscous fiber 10.0 g/1,000 kcal, and almonds 14 g/1,000 kcal) in a crossover trial. Participants, recruited as in previous studies, were assigned in random order to all 3 groups. TC and LDL cholesterol concentrations decreased significantly in participants in the lovastatin and portfolio groups. However, subjects taking lovastatin lowered TC and LDL cholesterol to a significantly greater extent than those following the portfolio diet (p = 0.013).
tested the portfolio diet in a less restrictive, “real-world” environment. Participants, recruited from 2 sets of newspaper advertisements in the Toronto area and from an earlier study, were instructed to consume a low–saturated fat (<7% of calories) and low-cholesterol (<200 mg/day) diet for 2 months before study onset. All participants were then instructed to follow a portfolio diet. Food was not provided. After 1 year, participants experienced significant reductions in plasma lipid concentrations. This study did not include a control group, relying on baseline values and previous control measures in about 1/2 of the studied subjects. The investigators reported that a significant correlation was found between dietary adherence and change in LDL cholesterol (r = −0.42, p <0.001).
Our review demonstrates that individuals following plant-based diets experience significantly lower blood lipid concentrations compared to those following diets that include animal products. In observational studies, vegetarians also appear to have fewer and smaller age-related increases in lipids compared to nonvegetarians.
Although it is difficult to directly compare the effects of dietary interventions from various studies, the reviewed studies suggest that a greater reduction in dietary animal products yields greater reductions in lipid levels. In randomized controlled trials, compared to baseline values, primary plant-based and ovolactovegetarian dietary interventions were associated with decreases of TC and LDL cholesterol of about 10% to 15%, vegan dietary interventions were associated with decreases of approximately 15% to 25%, and combination dietary interventions (vegetarian diets with additional fiber, soy, and nuts) were associated with decreases of approximately 20% to 35%. The studies were not subjected to a meta-analysis. Although the combination dietary interventions prescribed by Jenkins et al
contained varying amounts of plant sterols, soy protein and isoflavins, viscous fibers, and nuts, other plant-based diets in the reviewed trials contained some or all of these components in unknown amounts, making direct comparisons difficult.
Like all cholesterol subfractions, HDL cholesterol is typically lower in vegetarians compared to nonvegetarians. Trials of low-fat vegetarian diets, in which carbohydrates replace fats, have demonstrated decreases in HDL cholesterol. The mechanism for the effect of diet on HDL cholesterol is unclear, but lower apo A-1 production rates have been suggested as a contributing factor.
showed decreases in atherosclerotic lesions and cardiac events in subjects following an intervention including a low-fat vegetarian diet and moderate exercise, even in those with decreased HDL cholesterol. Also, although long-term adherence to a vegetarian diet is consistently associated with lower plasma triglyceride concentrations, randomized trials have demonstrated varied effects on triglycerides. Although diets high in refined carbohydrates may increase triglyceride concentrations, high-fiber and low–glycemic index foods appear to have the opposite result.
Plant-based diets reduce plasma cholesterol concentrations through several mechanisms. Reduced dietary intake of total fat, saturated fat, and cholesterol leads to less absorption and conversion to blood cholesterol.
AHA Science Advisory Stanol/sterol ester-containing foods and blood cholesterol levels. A statement for healthcare professionals from the Nutrition Committee of the Council on Nutrition, Physical Activity, and Metabolism of the American Heart Association.
due to isoflavin (genistein and daidzein) effects. Markers of cardiovascular health, such as decreased C-reactive protein, LDL cholesterol particle size, and increased resistance to oxidation of LDL cholesterol, have been associated with the intake of monounsaturated fats, nuts, and fruit and vegetables.
Compared with other therapeutic diets, plant-based diets have the advantage of not requiring macronutrient content calculations or portion-size control. Plant-based diets are also high in fiber, improving satiety, which sets them apart from calorie-restricted weight-loss diets. With adequate planning, vegetarian diets meet all nutritional needs.
Dietary trials have certain limitations. Dietary intervention studies typically cannot be double blinded. Study interventions (type of dietary intervention, degree of fat restriction, and duration) and end points vary, making direct comparisons and meta-analyses difficult. Most of the studies reviewed were observational studies or randomized controlled trials with relatively small sample sizes and brief intervention periods. Confounding factors such as different baseline cholesterol levels, baseline diets, glucose homeostasis, insulin sensitivity, and body fat composition and distribution can affect the effectiveness of dietary interventions. Few studies have examined the effect of diet on morbidity or mortality. Long-term, large prospective studies, with consistent diets and outcomes, may clarify questions surrounding the effects of plant-based diets on cardiac and total mortality, effects in patients already treated with lipid-lowering medications and associated direct and indirect costs.
Hypercholesterolemia and associated coronary artery disease, peripheral vascular disease, and stroke are major contributors to morbidity, mortality, and health care costs. The treatment of dyslipidemia accounts for significant costs and potentially adverse effects. Dietary changes are recommended as first-line therapy for dyslipidemia because they are safe and cost effective. However, to date, studies have shown NCEP diets and similar regimens to be only modestly effective, reducing TC and LDL cholesterol concentrations by 5% to 10%. However, plant-based diets, which follow the current recommendations of the Third Adult Treatment Panel and the American Heart Association, have demonstrated greater cholesterol reductions and are a preferable option for cholesterol reduction.
Ten-year mortality from cardiovascular disease in relation to cholesterol level among men with and without preexisting cardiovascular disease.
Ferdowsian and Barnard1 have presented important information about populations following plant-based diets, particularly vegetarian (VEG) and vegan, suggesting that they are at lower risk for ischemic heart disease mortality.