May 25, 2023

expert reaction to analysis of trials looking at vegetarian and vegan diets and levels of cholesterol and fats in the blood

A meta-analysis published in the European Heart Journal looks at vegetarian and vegan diets and blood lipids.

Dr Duane Mellor, Registered Dietitian and Senior Lecturer, Aston Medical School, Aston University, said:

“This is an interesting analysis of previously published clinical trials comparing various types of vegetarian and vegan diets with an omnivorous diets with respect to effects on cholesterol and a protein linked to cholesterol which is recognised as a risk factor for heart disease – apolipoprotein B.

“It is important to recognise that both the types of vegan and vegetarian diets as well as the comparison omnivorous diets which included meat varied considerably between studies, with a number of the studies which showed the greatest beneficial effects being vegan and vegetarian diets which are lower in fat.  It is also noticeable that a number of the studies which showed the greatest benefits in terms of reduction of cholesterol and apolipoprotein B were led by people who are known advocates of vegan diets.

“Although a vegetarian and vegan diet can be very healthy and beneficial with respect to cardiovascular risk, it is important that it is well planned so that nutrients it can be low in are included including iron, iodine, vitamin B12 and vitamin D.  If someone is thinking about making a dietary change, it can be useful to discuss these with a health professional and perhaps a dietitian so that it is designed to be nutritionally adequate, help address their health concern and ideally be enjoyable.”

Tracy Parker, Senior Dietitian at the British Heart Foundation (BHF), said:

“This large analysis supports what we already know: that including more plant-based foods in your diet is good for your heart and the environment.  However, this study only looked at people eating strict vegan and vegetarian diets over a short period of time, and some people can find it hard to consistently follow these diets long-term.

“Some may find it easier to follow a Mediterranean-style diet that features plenty of fruit, vegetables, pulses, wholegrains, fish, eggs and low fat dairy, with only small amounts of meat.  There is considerable evidence that this type of diet can help lower your risk of developing heart and circulatory diseases by improving cholesterol and blood pressure levels, reducing inflammation, and controlling blood glucose levels.  If you want to make healthy changes to your diet, a great place to start is the Eatwell guide, which is the basis for our healthy eating recommendations in the UK.”

Dr Ian Johnson, Nutrition researcher and Emeritus Fellow, Quadram Institute, said:

“The new study by Koch and colleagues is a meta-analysis of randomised trials designed to explore the effects of vegan and vegetarian diets on blood lipids associated with risk of cardiovascular disease in humans.  Randomised controlled trials are the gold standard for investigating the impact of any intervention on human health, but applying this approach to the study of human nutrition is particularly difficult.  By pooling and analysing the results of the relatively small number of such studies on plant-based diets and blood lipids and lipoproteins undertaken between 1980 and 2022, the authors have been able to explore the issue in depth, and to show consistent, potentially beneficial effects of vegan and vegetarian dietary patterns on cholesterol, low-density lipoprotein cholesterol and apolipoprotein B.  Although it is not possible to entirely eliminate all the various sources of bias in these types of study, the authors have considered this problem and their results appear to be robust.  Importantly they are also consistent with the many observational studies on vegetarian diets that have been conducted over several decades.  In general, adherence to vegetarian and other types of plant-based dietary pattern has been shown to be associated with healthier lipid profiles and reduced risk of ischaemic heart disease, in comparison to consumers of diets containing fewer plant foods and higher levels of animal products.

“This new report is consistent with current dietary recommendations in the UK and elsewhere, which advocate a reduction in the consumption of red and processed meat, and an increase in the consumption of fruits, vegetables, and wholegrain cereal products.  It is important to be aware however that some vegan and vegetarian dietary patterns may be low in essential minerals and vitamins, and that if consumption of animal products is eliminated entirely, the use of micronutrient supplements should be considered.”

Prof Aedin Cassidy, Chair in Nutrition & Preventative Medicine, and Director for Interdisciplinary Research in the Institute for Global Food Security, Queen’s University Belfast, said:

“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.”

Prof Robert Storey, Professor of Cardiology, University of Sheffield, said:

“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.”

Prof Tom Sanders, Professor emeritus of Nutrition and Dietetics, King’s College London, said:

“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.”

Dianne P Reidlinger and others, Cardiovascular disease risk REduction Study (CRESSIDA) investigators, How effective are current dietary guidelines for cardiovascular disease prevention in healthy middle-aged and older men and women? A randomized controlled trial, The American Journal of Clinical Nutrition, Volume 101, Issue 5, May 2015, Pages 922–930, https://doi.org/10.3945/ajcn.114.097352

Tong et al. Risks of ischaemic heart disease and stroke in meat eaters, fish eaters, and vegetarians over 18 years of follow-up: results from the prospective EPIC-Oxford study. BMJ 2019;366:l4897 https://doi.org/10.1136/bmj.l4897

Prof Martin Warren, Chief Scientific Officer, the Quadram Institute, said:

“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.”

‘Vegetarian or vegan diets and blood lipids: a meta-analysis of randomized trials’ by Caroline A. Koch et al. was published in the European Heart Journal at 00:05 UK time on Thursday 25 May 2023.

DOI: 10.1093/eurheartj/ehad211

Declared interests

Dr Duane Mellor: “I am a vegetarian.”

Tracy Parker: “None to declare.”

Dr Ian Johnson: “No interests to declare.”

Prof Aedin Cassidy: “I have no interests to declare.”

Prof Robert Storey: “No relevant COI.”

Prof Tom Sanders: “Honorary Nutrition Director to HEART UK.”

For all other experts, no reply to our request for DOIs was received.