Plant-based diets associated with lower levels of plasma lipids by meta-analysis

23 Aug 2017 --- Consumption of vegetarian diets, particularly vegan diets, is associated with lower levels of plasma lipids, which could offer individuals and healthcare professionals an effective option for reducing the risk of heart disease or other chronic conditions. This is the finding of a review and meta-analysis by Dr. Yoko Yokoyama, Ms. Susan Levin and Dr. Neil Barnard.

The study aimed to answer the question of what evidence from clinical trials and observational studies proves that plant-based diets (defined as vegetarian or vegan diets) influence blood cholesterol concentrations. The range of plant-derived foods is described as “enormous,” including simple fruits, vegetables, beans, and whole grains as well as products that are processed and prepared with a variety of additional ingredients.

Disease association
Elevated blood concentrations of low-density lipoprotein cholesterol are known to be associated with increased risk of coronary heart disease. Although lowering concentrations can reduce cardiovascular deaths, the report notes that hyperlipidemia is still underdiagnosed and undertreated. It also notes that a 10 percent increase in the prevalence of treatment for hyperlipidemia could prevent an estimated 8,000 deaths per year.

The review goes on to state that it has been further estimated that even modest steps, such as those proposed by the National Cholesterol Education Program Adult Treatment Panel primary prevention guidelines, could prevent approximately 20,000 heart attacks and 10,000 deaths due to coronary heart disease and save almost US$3 billion in heart disease-related medical costs per year.

Although low-density lipoprotein cholesterol has been the primary lipoprotein of concern, total cholesterol, high-density lipoprotein cholesterol and triglycerides also play roles in heart disease risk. In the study, “plasma lipids” refers to the group of lipids including total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and triglycerides. The study emphasizes that modifiable factors – including diet, weight and exercise – may play significant roles in developing hyperlipidemia.

Lower concentrations
The researchers’ meta-analysis of 30 observational studies and 19 controlled trials shows that, compared with consumption of omnivorous diets, consumption of vegetarian diets is associated with lower plasma lipid concentrations. The meta-analysis shows overall differences in total cholesterol of −29.2 mg/dL in observational studies and –12.5 mg/dL in clinical trials and differences in LDL-C of −22.9 mg/dL in observational studies and −12.2 mg/dL in clinical trials.

High-density lipoprotein cholesterol was also lower in vegetarian groups than in omnivorous groups, although the degree of difference was relatively modest (−3.6 mg/dL in observational studies and −3.4 mg/dL in clinical trials).

The meta-regression and subgroup analysis showed that the duration of adherence to a vegetarian diet did not modulate the observed effects of the diet. However, younger age was associated with lower TC and LDL-C, suggesting that an effect of diet duration may play a role. Additionally, the present analysis could not adjust for dietary compliance. Further studies are needed to clarify the relation between the duration of vegetarian diets and its effect on plasma lipids.

The review notes that the strengths of the present meta-analysis include a large sample size that lends confidence to these findings and allowed subgroup analyses in specific population groups. In addition, the focus of the meta-analysis on food consumption as opposed to supplements or other artificial interventions makes the findings applicable to the public.

Although not all clinicians have the training or time to confidently guide patients toward healthful vegetarian diets, registered dietitians can provide the services necessary to assist patients in making this transition, the review adds.

The full review and meta-analysis is available here.