Whilst we have gone into depth on the pathophysiology of  how red/ processed meat affects CVD risk, there is also a wealth of epidemiological evidence – and disagreement – on the subject. The Seven Countries Study⁴² sparked current interest, as it was the first to find a significant correlation between red meat and CVD. Since, many studies have agreed, linking red meat with stroke and ischaemic heart disease⁴³, atherosclerosis⁴⁴, and acute coronary syndrome⁴⁵.

However more recently, scrutiny has changed to the processing procedures of meats. Micha et al.‘s large meta-study found the increased salt and preservatives in processed meat to be the disease causing mechanism rather than the fat content found in all red meat, only finding a link between CVD and processed meats¹¹. However, there are conflicting studies which claim that while processed red meat is indeed more detrimental to cardiovascular health, unprocessed red meat is still associated with a 13% increased risk of death from cardiovascular causes for every additional daily portion⁴⁶.

Whilst associations aren’t always consistent, there is enough significant evidence to link processed red meat consumption with CVD. Whether unprocessed red meat consumption is also a risk factor is more controversial, and difficult to assess as diet is very complex, as are the mechanisms and risk factors for CVD. These inconsistencies limit the reliability of current recommended intakes for red meat. The government’s current guidelines, issued by the Department of Health, recommend that anyone eating more than 90g of red/processed meat per day should aim to cut down to 70g a day, which is the UK daily average⁴⁷. This recommendation is based on links between eating these foods and bowel cancer, but does not evaluate or provide information on red/processed meat intake as a risk factor for CVD. Considering that coronary heart disease is the leading cause of death in the UK and worldwide¹, this is not something to be overlooked.

For example, Pan A et al.¹⁹ estimated from analysis of two large cohort studies that by reducing the amount of red/processed meat eaten a day by half, to around 42g, 9.3% of deaths in men and 7.6% of deaths in women could be prevented. This same research found a dose-response relationship between red meat intake and all-cause mortality, which is a good basis to recommend cutting down consumption.

The EPIC study⁴⁸ looked at meat consumption and mortality across 10 European countries, considering a very heterogeneous diet across a large sample size. It found no statistically significant associations between red meat intake and CVD, but concluded that Europeans consuming high amounts of processed meat are at an increased risk of an early death, especially due to CVD. Furthermore, it was estimated that 3.3% of deaths could be prevented if these men and women ate less than 20g of processed meat a day. Current government guidelines⁴⁷ don’t reflect this advice, as they don’t highlight that processed meat is considered to have a greater negative impact on health^11,19,48,49 than unprocessed red meat in their dietary recommendations.

However, it is important to take into consideration other confounding factors when looking at complex disease processes such as those involved with CVD. Men and women with a higher intake of red meat are more likely to be current smokers, to drink alcohol and to have a higher BMI. They are less likely to consume fruits and vegetables and to be physically active ^19,48. All of the above are key determinants in the risk of developing cardiovascular disease^50,51,52. This could imply that in fact red/processed meat consumption is not a significant risk factor in the development of CVD, but rather a confounding factor of another variable. Researchers adjusted data to eliminate the aforementioned confounding variables^{11,19, 48,51} but these statistical adjustments may not be significant enough. For example, a low socioeconomic status is associated with eating more processed foods and fattier, cheaper cuts of meat⁵³. It is also strongly associated with increased prevalence of smoking⁵⁴, obesity⁵⁵ and lower consumption of fruits and vegetables⁵⁴. Therefore it could be the case that the trends between red/processed meat consumption and CVD are actually due to the overarching factor of socioeconomic status.

To work around this, we can look at studies of populations with very similar health behaviours, with meat intake being one of the only significant variables. Epidemiological study of Adventists, a Christian denomination, allows one such opportunity, as the Church doctrine places a strong emphasis on healthy living, including abstinence from tobacco and alcohol⁵⁶. Vegetarianism is also encouraged by the Church, with around 50% of Adventist members following a vegetarian diet and the rest following a diet similar to the rest of the western population⁵⁷. One review of three large Adventist Cohorts found that vegetarians had greatly reduced risks of developing hypertension, type-2 diabetes, metabolic syndrome and obesity which can explain why in all three cohorts analysed, vegetarians had 26% to 68% lower risks of mortality from ischaemic heart disease, CVD, and cerebrovascular disease⁵⁷. These figures were significant even having been adjusted for age, sex, smoking status, race, educational level, alcohol and other factors related to CVD. These results back up the epidemiological and pathophysiological evidence we have previously reviewed – that reduction in consumption of meat is cardio-protective.  Another study analysing mortality between vegetarians and non-vegetarians found that vegetarians had an ischemic heart disease death rate ratio of 0.78 compared to non-vegetarians, and that even ‘semi-vegetarians’ (those who ate fish only or meat less than once a week) had a death rate reduction of 0.66 implying that a reduction in meat consumption is still beneficial, if not as good as abstinence.

Benefits

When considering how much red meat to consume you must not only look at the detrimental effects but also the benefits. Red meat is nutritional and a source of vitamins and minerals that are essential to health. A 100g portion of raw ground beef contains 36%, 29% and 84% of your Vitamin B3, B6, and B12 recommended daily nutrient intakes (RNIs) respectively. It also provides 20% of your Iron, 66% of your Zinc and 28% of your Selenium RNIs.⁵⁸ Red meat is a better source of haem iron than either poultry or fish, and also more bioavailable than non-haem iron from plant sources. Iron-deficiency anaemia is a major nutritional problem affecting high and low socioeconomic populations worldwide.⁵⁹ Red meat is also the largest source of Vitamin B12 in the diet with just 100g supplying nearly your entire daily-recommended intake.  The methylation cycle occurs in all cells in the body and it requires adequate levels of B12 as well as B6 and folate. Without these nutrients the enzymes cannot function properly leading to increased levels of homocysteine – a risk factor for cardiovascular disease and stroke.  So in moderation red meat can have protective effects.⁵⁹