In the scientific field, it is essential to carry out comprehensive studies that compile all available information on certain topics. This is particularly relevant in the field of nutrition, as the results of this information gathering are often used to provide dietary recommendations to the population. In this respect, meta-analyses such as this one play a key role, especially when they compile information from randomised controlled clinical trials, which provide a solid scientific evidence base. 

This particular study focuses on the growing body of scientific information available on the health of plant-based diets, whether vegetarian or vegan. It analyses data from 30 clinical trials conducted over more than 40 years. As a result, the authors show that plant-based diets reduce levels of total cholesterol, LDL-cholesterol and, most importantly, apolipoprotein B by 7%, 10% and 14%, respectively. This provides the highest degree of scientific evidence possible. 

Therefore, these results support the existing knowledge on the subject. However, it is important to note that their implications are currently limited for several reasons. Firstly, the role of plasma cholesterol and LDL-cholesterol in cardiovascular disease has been questioned in recent years. It has been shown that it is the modified LDL particles that have the ability to contribute to the thickening of arteries and thus to the development of cardiovascular disease. One of the most common modifications is oxidation. Unfortunately, the study does not assess the effect of the aforementioned diets on plasma concentrations of oxidised LDL. Secondly, the study does not distinguish between the two types of apolipoprotein B (48 and 100), which are associated with both cholesterol and triglyceride transport, especially in the postprandial period, just after food intake. Since the 1990s, some scientists have suggested that atherosclerosis, i.e. abnormal thickening of the arteries, is actually a disease that occurs after eating. Thirdly, no differences were found in plasma triglyceride levels, whose contribution to this disease is becoming increasingly important. 

In summary, this study consolidates current knowledge on the role of plant-based diets in blood lipid control. However, it does not add much new to what is already known.

This is an important summary of the available trials on vegan and vegetarian diets and their impact on improving cholesterol levels.  There is growing evidence that plant based diets influence our health and diets characterised by high quality plant based foods and lower intakes of animal products may be beneficial for health irrespective of established health conditions and genetic disposition.  However, not all plant based diets are equal with only healthy plant based diets, characterised by fruits, vegetables, wholegrains improving health and not other plant diets (e.g. those including refined carbohydrates, processed foods high in fat/salt etc.).  Improving lipids provides a mechanistic insight into how plant based diets have the potential to improve heath but this is one of many potential mechanisms including impact on blood pressure, weight maintenance, and blood sugars.

This work represents a well-conducted analysis of 30 clinical trials involving over two thousand participants and highlights the value of a vegetarian diet in reducing the risk of heart attack or stroke through reduction in blood cholesterol levels.  However, it also demonstrates that the impact of diet on an individual's cholesterol level is relatively limited.  This is because people inherit the tendency for their livers to produce too much cholesterol, meaning that high cholesterol is more strongly influenced by our genes (DNA) than by our diet.  This explains why statins are needed to block cholesterol production in people who are at higher risk of, or have already suffered from, a heart attack, stroke or other illness related to cholesterol build-up in blood vessels.

Observational studies find vegans and to a lesser extent vegetarians have lower levels of low density lipoprotein (LDL) cholesterol.  This new study is a review of published randomized controlled of trials of vegetarian/vegan diets on blood lipoproteins particularly low density lipoprotein (LDL) cholesterol.  The average reduction in LDL cholesterol (0.3 mmol/) was similar to the change observed in a large trial comparing the UK recommended diet (which was not vegetarian) with a traditional British diet (Reidlinger et al. 2015).  It is likely that much of the difference is brought about by lower intakes of saturated fatty acids and higher intakes of fibre.

A limitation of this review is that most of studies were on vegetarian diets, which include dairy foods which are high in saturated fat, and only a few were vegan diets.  The largest reductions were on the Ornish diet which is a very low fat diet.  A vegan diet would be expected to have a larger effect on LDL cholesterol because of their lower saturated fatty acid intake to result in lower LDL cholesterol levels.  The environmental impact of a vegan diet on greenhouse gas emissions is also lower because of the absence of dairy products.

Large trials with cholesterol lowering medication show a 1 mmol reduction in LDL cholesterol is associated with a 10% reduction in cardiovascular disease (CVD) mortality and a 20% reduction in CVD events.  Translating the findings of the review suggest that the LDL lowering effect of a vegetarian/diet would be expected to decrease risk of fatal and non-fatal CVD by 3% and 6% respectively.  These findings are consistent with observational studies that find vegetarians/vegans have a lower incidence of ischemic heart disease but not stroke.

This is an interesting paper that represents a comprehensive and structured review of existing studies, employing a statistical technique that combines the results of multiple studies to provide a quantitative summary of the evidence that vegetarian and vegan diets significantly reduce cholesterol and apolipoprotein B (the latter being a major component of low density lipoprotein particles – or bad cholesterol).

The paper has selected diets that are recognised as healthy – so perhaps it is not that surprising that the outcomes are so favourable.  The paper confirms that healthy, balanced vegan and vegetarian diets have significant benefits in terms of reducing some of the main factors that are associated with plaque formation and progression in the arteries, which is referred to as atherosclerosis.  Reducing levels of cholesterol and apolipoprotein A therefore reduces the risk of atherosclerotic cardiovascular disease risk, thereby reducing the risk of cardiovascular events such as heart attack or stroke.

Of course, both vegetarian and vegan diets are associated with promoting sustainability through reducing environmental impacts of animal farming so there are benefits here as well.  However, animal-based products such as meat do represent nutrient-dense foods that have other benefits.  Similarly, crop-based diets can be low in certain micronutrients – so in general, reducing meat consumption but maintaining a broad and varied diet is good for health.