Conclusions Plant-based diets are associated with decreased total cholesterol , low-density lipoprotein cholesterol , and high-density lipoprotein cholesterol , but not with decreased triglycerides .
Context Although a recent meta- analysis of r and omized controlled trials showed that adoption of a vegetarian diet reduces plasma lipids , the association between vegetarian diets and long-term effects on plasma lipids has not been subjected to meta- analysis .
Objective The aim was to conduct a systematic review and meta- analysis of observational studies and clinical trials that have examined associations between plant-based diets and plasma lipids .
The Effect of a Plant-Based Diet on Plasma Lipids in Hypercholesterolemic Adults
Context People can achieve recommended fat intake while consuming high or low amounts of vegetables , fruits , legumes , and whole grains . Contribution This 4-week r and omized trial compared 2 diets with different vegetable , fruit , legume , and whole-grain content but identical total fat , saturated fat , protein , carbohydrate , and cholesterol content . The 59 adults who consumed high amounts of vegetables , fruits , legumes , and whole grains  had greater improvements in total and low-density lipoprotein cholesterol levels than the 61 adults who ate low amounts of these foods . Implication s At least over the short term , greater improvements in low-density lipoprotein and total cholesterol are an additional benefit of diets high in vegetables , fruits , legumes , and whole grains . The Editors It is well established that elevated low-density lipoprotein ( LDL ) cholesterol concentrations are a risk factor for cardiovascular diseases and that dietary modification is considered a first approach to their treatment and control ( 1 , 2 ) . For several decades , dietary modification for lipid management traditionally focused on avoiding saturated fat and cholesterol ( 3 - 5 ) . Previous examples of dietary interventions targeting LDL cholesterol level often reported only modest lipid improvements , leading some to consider diet a relatively ineffective therapy ( 6 ) . However , recent developments have suggested that the traditional focus of lipid management may have been overly simplistic and that diets might be more effective if more attention was focused on including certain foods or factors rather than just avoiding saturated fat and cholesterol . Effective refinements of dietary strategies for lipid management could decrease the gap in effectiveness between dietary approaches and drug therapy . Several dietary factors or foods , including soy protein , soy isoflavones , plant sterols , soluble fiber , oats , nuts , and garlic , have established or potential lipid benefits ( 7 - 13 ) . Each is derived from plant food sources , and it is inclusion of these factors , rather than avoidance , that is reported to confer benefits . However , given that most plant foods contain low or negligible amounts of saturated fat and that all plant foods are devoid of cholesterol , it follows that a plant-based diet is inherently low in saturated fat and cholesterol . Therefore , it is difficult to distinguish between plasma lipid benefits derived from the actual plant-based dietary components and those derived from avoidance of saturated fat and cholesterol . Several studies have been design ed to test the effects on plasma lipids of diets with identical saturated fat and cholesterol intake but varied amounts of 1 or 2 additional dietary components ( 14 - 16 ) . Data are more limited on dietary approaches that hold saturated fat and cholesterol intake constant while modifying multiple other dietary components simultaneously ( 17 ) . Modifying multiple dietary components simultaneously ( for example , increasing intake of vegetables , fruits , and low-fat dairy ) while holding sodium intake constant has been shown to effectively lower elevated blood pressure in the Dietary Approaches to Stop Hypertension trials ( DASH I and II ) ( 18 , 19 ) . Testing a parallel approach to refining dietary intervention for lipid management is warranted . In 2000 , the American Heart Association ( AHA ) reported revised dietary guidelines that substantially modified its 1993 and 1996 guidelines ( 2 , 4 , 5 ) . All 3 versions of the guidelines recommended keeping saturated fat intake at less than 10 % of energy and cholesterol intake below 300 mg/d . A notable modification of the 2000 guidelines was to emphasize foods and overall eating patterns , including increased intakes of vegetables and whole grains ( in general , a plant-based diet ) . It was our hypothesis that a plant-based diet consistent with the revised AHA 2000 guidelines would increase the LDL cholesterol-lowering benefits of the previous AHA Step I guidelines . We theorized that this improvement would be independent of the plant-based diet 's saturated fat and cholesterol content . Therefore , we design ed 2 diets that had identical levels of total fat ( 30 % of energy ) , saturated fat ( 10 % of energy ) , and cholesterol ( < 300 mg/d ) but differed substantially in content of nutrient- and phytochemical-dense plant-based foods . The purpose of the study was to determine whether LDL cholesterol-lowering benefits among adults with moderately elevated cholesterol levels  would be greater under weight-stable conditions with a plant-based low-fat diet than with a more typical , convenience-oriented low-fat diet that was identical in intake of total fat , saturated fat , and cholesterol . Methods Participants Participants were recruited from the local community , primarily through newspaper advertisements , letters to previous study participants , and flyers sent to university employees . Men and women were invited to enroll if they were 30 to 65 years of age with fasting plasma LDL cholesterol levels of 3.3 to 4.8 mmol/L ( 130 to 190 mg/dL ) , fasting plasma triglyceride levels less than 2.83 mmol/L ( < 250 mg/dL ) , body mass index between 19 and 31 kg/m2 , and a current diet estimated to derive at least 10 % of energy from saturated fat . Pregnant women , persons who smoked , persons with prevalent heart disease or diabetes , or persons who had been using lipid-lowering or blood pressure-lowering medications within the past month ( all determined through self-report ) were excluded . During the recruitment phase , 1096 individuals were screened by telephone interview and 345 who met the initial inclusion criteria were considered eligible for cholesterol testing . Of these 345 persons , 188 who were found to have eligible concentrations of LDL cholesterol and triglycerides attended an orientation meeting . Fifty-one persons decided not to participate ( primarily because of the time commitment ) , and an additional 12 potential participants were excluded after a 3-day food record showed that their estimated average intake of saturated fat was already less than 10 % of energy . One hundred twenty-five participants were r and omly assigned to 1 of the 2 diet groups . The Stanford University Human Subjects Committee review ed and approved the investigation , all participants signed an informed consent form before enrollment , and the study was performed according to Declaration of Helsinki guidelines ( 20 ) . Design The trial used a parallel design . We r and omly assigned participants in blocks of 20 by selecting , without replacement , from a set of indistinguishable envelopes containing 10 assignments to each of the 2 diet groups . R and omization of the envelopes was done by h and , without a computer algorithm . No stratification criteria were used . Each participant was provided with meals , snacks , and beverages on an outpatient basis for 28 days , as described later . Diets Both study diets were design ed to provide 30 % of energy from total fat , 10 % of energy from saturated fat , and approximately 100 mg of cholesterol per 1000 kcal per day . During the menu- design ing stage of the study , the nutrient composition of the diets was determined by using the data base of Food Processor software , version 7.0 ( ESHA Research , Salem , Oregon ) . Menus were design ed by using commonly available foods from local markets . The Low-Fat diet was design ed to include many reduced-fat prepared-food items ( for example , reduced-fat cheeses , low-fat frozen lasagna , and low-fat and sugar-rich snack foods ) . In contrast , the Low-Fat Plus diet was design ed to include considerably more vegetables , legumes , whole grains , and fruits . Butter , cheese , and eggs were added to the daily menus for the Low-Fat Plus diet , increasing the saturated fat and cholesterol content to match the Low-Fat diet . A 7-day menu cycle was design ed for each of the 2 study diets ; therefore , each menu was repeated 4 times during the 28 days . The diets included breakfast , lunch , dinner , beverages , and snacks for each day . Each weekday , the participants ate either lunch or dinner at the dining facility of the Stanford General Clinical Research Center . After their on-site meal , they were given coolers that contained meals and snacks to be consumed off-site . On Fridays , participants received weekend meals to be consumed off-site . Appendix Table 1 and Appendix Table 2 list the daily menus . One free-choice evening meal was allowed each weekend . For this meal , participants were given guidelines for choosing low-fat meals consistent with their diet assignments and were required to keep a record of foods consumed . These records were analyzed for nutritional content and were used to determine the impact of the free-choice meals on the overall study diets . Adherence was measured by using daily log sheets kept by participants that tracked incomplete consumption of study foods or consumption of any non study foods . The 28 daily food logs for each participant were examined for deviations from the diets . The energy contribution of each deviation was determined and then totaled for the entire 28-day protocol period . Each of the 14 daily menus ( 7-day cycle 2 diets ) was analyzed chemically for nutrient content before the study and then again during the study ( Covance Laboratories , Madison , Wisconsin ) . The chemical analyses performed before the study confirmed that the average composition of the daily menus provided 30 % of energy from total fat , 10 % of energy from saturated fat , and approximately 100 mg of cholesterol per 1000 kcal per day . When the 2 diets were first design ed , we attempted to match their mono- and polyunsaturated fat content . However , the data base used in the design phase was missing values for these nutrients for approximately 20 % of the foods . In addition , many of the specific products purchased locally for the study provided incomplete information for the content of these unsaturated fats . The first round of chemical analyses of the diets , performed before enrollment began , indicated a modest discrepancy
Conclusions Plant-based diets are associated with decreased total cholesterol , low-density lipoprotein cholesterol , and high-density lipoprotein cholesterol , but not with decreased triglycerides .
Context Although a recent meta- analysis of r and omized controlled trials showed that adoption of a vegetarian diet reduces plasma lipids , the association between vegetarian diets and long-term effects on plasma lipids has not been subjected to meta- analysis .
Objective The aim was to conduct a systematic review and meta- analysis of observational studies and clinical trials that have examined associations between plant-based diets and plasma lipids .