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red-meat-and-health

Red Meat and Health


by Matt Durkin
MSc Nutrition Specialist
06/02/2020


There are many topics that cause both disagreement and confusion in nutrition, but red meat and health is certainly one of the most hotly debated.

It seems we cannot go a week without seeing a headline that claims red meat is bad for health, be it cancer, heart disease, or metabolic complications like diabetes. Some of these headlines can be quite outlandish, remember the: “red meat is as deadly as smoking” claim? Just as soon as there is a publication making such claim, up pops a study which indicates that red meat isn’t bad after all.

This can be confusing as well as frustrating for those who are looking for evidence-based ways to improve their health and wellbeing. So in a bid to help, we thought it would be a good opportunity to have an unbiased look at the evidence we currently have. 

Please note, this article will assess the relationship between red meat and health specifically and won’t cover other important aspects such as environmental or ethical concerns.  

The Issues with Epidemiology

In science, the ‘gold standard’ of research is a randomised control trial – a study which randomly assigns participants to 2 (or more) groups to test a specific treatment. For example, one group may receive an innovative drug and the other group a placebo. Then, scientists can compare the results after a certain time to gauge the effectiveness of the treatment(s).

As good as RCT’S are, they are often prohibitively expensive and in certain cases unethical. Instead, researchers often look for answers to their questions by conducting a type of study known as epidemiology.  These studies analyse data and try to finds relationships between one factor (red meat consumption) and another (heart disease).

I am sure you have heard the saying ‘correlation doesn’t equal causation’ and this is the problem with epidemiology. Only in very special circumstances when the evidence is extremely strong can these studies prove causality. One example is smoking and lung cancer. 

There are also valid criticisms of nutrition epidemiological studies that merit discussion. One of these is the tools that researchers use to assess dietary habits. More often than not, food frequency questionnaires are used. Although cost-effective, easy to complete and simple to analyse, they can be massively inaccurate due to deliberate bias or forgetfulness. 

Other downsides are that the results are specific to the population they were taken from, meaning generalisations are difficult. It is also harder, but not impossible, for researchers to control and account for other lifestyle factors which can influence health.

Now that you appreciate the strengths and limitations of the way that researchers garner their data, let’s have a look at the current state of play…

Red Meat and Cancer 

Although not unanimous, the research seems pretty clear that red and processed meat is strongly linked to bowel cancer, with there being some evidence for other types of cancer such as stomach, breast and prostate.

Resultantly, the World Health Organisation has classified processed meat (bacon, sausages, deli meats etc.) as a class 1 carcinogen (“causes cancer”) and unprocessed red meat as class 2A (“probably causes cancer”). 

Sensationalist headlines have compared processed meats to asbestos, ionizing radiation, plutonium and tobacco smoke, given that these are also class 1 carcinogens. Although this is true, the key element they often forget to include is how many incidences of cancer these things cause. 

For example, research cited by Cancer Research UK has shown that 21% of bowel cancers are caused by too much red/processed meat, whereas almost 90% of all lung cancers are caused by tobacco smoke. Looking in absolute terms, it is estimated that 34,000 deaths from cancer annually are because of red/processed meat which is far fewer than the cancer deaths caused by alcohol (600,000) and tobacco smoke (1,000,000). 

However, just because one thing is less carcinogenic than another that doesn’t make it okay. Due to this, nutrition guidelines worldwide are recommending that we cut down on our intake of red meat and either avoid processed meat entirely or have it very occasionally. 

But what is it about red and processed meat that is carcinogenic? Well there seems to be a few culprits. Firstly, red and processed meat is rich in heme iron - a compound which can cause cell damage. Similarly, processed meats contain nitrates to keep them fresher for longer, but these are also linked to the creation of harmful bacteria in the body. Finally, cooking meat at high temperatures creates chemicals such as heterocyclic amines (HCAs) and polycyclic amines (PCAs) which are known to damage cells in the bowel. 

Interestingly, the iron from plants (non-heme) is not linked to any health issues. This is because the body can tightly regulate how much non-heme iron it absorbs, but the same cannot be said for the heme form. 

Red Meat and Heart Disease

The link between red meat and heart disease is not breaking news, as it was proposed over 50 years ago that red meat increases LDL (‘bad’) cholesterol which raises the risk of coronary heart disease. 
In 2017, the European Atherosclerosis Society Consensus Panel looked at genetic, epidemiological and clinical evidence when compiling their consensus statement on LDL cholesterol’s role in heart disease. 

They reported a dose-dependent and time-dependant relationship between LDL exposure to the blood vessel walls and atherosclerosis. Basically, if you have high LDL cholesterol and have it for a long time, you are at a greater risk of experiencing the narrowing of arteries - a hallmark of heart attacks and strokes. They also noted how dietary and pharmaceutical treatments for lowering LDL cholesterol have been consistently effective in reducing the prevalence of atherosclerosis. 

Similarly, there is the UK’s Scientific Advisory Committee on Nutrition report on saturated fat and health. It concluded that higher intakes of saturated fat lead to more cardiovascular events (heart attacks, strokes etc) but there was no relationship between saturated fat intake and death from heart disease. It also found that replacing saturated fat with unsaturated fat reduces cardiovascular events and deaths, but replacing this with carbohydrates or protein does not. So it seems that saturated fat isn’t quite as bad for heart health as first thought and if you cut down on it, it’s important what you replace it with. 

Scientists are now thinking that it may not be the saturated fat content of red meat that is the primary issue though. It has recently been discovered that meat-eaters and those with a typical high-fat western diet possess gut bacteria that use certain compounds in red meat to produce Trimethylamine N-oxide (TMAO). 

There are now multiple studies that have linked TMAO to the inflammation of blood vessels, impaired action of HDL (‘good’) cholesterol and blood clots. These mechanisms are thought to explain the positive correlation between TMAO and heart attacks and strokes. 

The good news is that it appears it only takes 4 weeks of no red meat to decrease TMAO back to a ‘normal’ level. What is also fascinating is that it appears vegetarians, vegans and those on a Mediterranean diet have much less bacteria in their guts to create TMAO. This is just one of the many reasons why national health guidelines are encouraging us to eat more plant-based foods. 

Red Meat and Obesity/Diabetes

The obesity and type 2 diabetes pandemic, termed ‘diabesity’ shows no signs of slowing down, but thankfully we are constantly learning how these two metabolic diseases can be reversed. 

Interestingly, research has consistently shown that eaters of red and processed meat are heavier and have a higher chance of developing diabetes than non-meat eaters. Unfortunately, the research doesn’t ascertain whether meat-eaters are heavier because they possess more muscle. However as the diabetes risk is clear, we can safely assume meat-eaters tend to carry more body fat. 

Published research has shown that for every 100g of red meat consumed daily, the risk of diabetes grows by 19%. What is more alarming is that for every 50g of processed meat eaten per day, the risk of diabetes soars by 51% compared to non-meat eaters. 

The good news is that replacing one serving of red or processed meat with nuts, low-fat dairy or whole grains is estimated to reduce diabetes risk by 16-35%. Not only have plant-based diets been shown to be good for diabetes risk reduction, they consistently lead to significant weight-loss when compared to other popular diets. 

This evidence is strong because the link between red meat intake and diabetes still persists even after the researchers controlled for body weight, as well as other factors such as age, race, smoking, blood pressure and physical activity. As white meat has a much weaker link to diabetes, this again suggests there is something within red and processed meats which is causing this.

Again, researchers believe heme iron to be an issue as it can damage the insulin-secreting cells of the pancreas. TMAO is also implicated because of the inflammation and the damage it causes to blood vessels. Impaired insulin secretion, inflammation and damage to blood vessels are all hallmarks of type 2 diabetes. 

It must be said that diets that include red meat can also reduce the risk of diabetes, or improve glucose control in those who do have diabetes. There are many studies that have shown that low-carbohydrate and ketogenic diets lead to weight loss, appetite management and improved insulin sensitivity which markedly reduces the risk of diabetes complications. This shows that there shouldn’t be a one-size-fits-all approach to diet. 

Health Benefits of Red Meat

Despite health concerns, red meat is actually very nutrient-dense as it contains a variety of essential nutrients in relevant amounts. Although beef, lamb, pork and other red meats vary in nutrient composition, they are generally good sources of riboflavin, niacin, vitamins B5, B6 and B12, zinc, selenium, phosphorus and choline. Red meat also contains some potassium, iodine, magnesium and copper. Red meat is also a good source of heme iron, but as we have found, too much appears to be harmful. 

Looking at macronutrients now, red meat is packed with bioavailable protein. It is classed as a ‘complete protein’ as contains all 9 essential amino acids – the ones we cannot make for ourselves. Because of the aforementioned reasons, less-developed countries are actually being recommended to consume more meat and animal products where possible. Conversely, in the developed world we more than achieve our protein requirements and there definitely wouldn’t be an epidemic of protein deficiency if we cut back on red meat. 

Recommendations

Although it would be in line with most national and international dietary recommendations to advise a more plant-based diet, it is extreme and unrealistic to tell people to totally stop eating red and processed meat. 

So then, many of you will be interested in what we can do to reduce health concerns. If this sounds like you, then give some of these points in the below list some thought. 

Summary

Hopefully this article has cleared-up a lot of the confusion around red meat and health, allowing you to confidently make better food choices. Red meat can certainly be part of a healthy diet given its nutritional quality. However it is pretty clear that we should be consuming less red meat generally speaking, instead focusing on seafood and plant-based sources which have proven health benefits. 


Sources
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6140446/
https://jech.bmj.com/content/55/12/905
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4154347/
https://www.cancerresearchuk.org/about-cancer/causes-of-cancer/diet-and-cancer/does-eating-processed-and-red-meat-cause-cancer
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6089671/
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/814995/SACN_report_on_saturated_fat_and_health.pdf
https://www.ncbi.nlm.nih.gov/pubmed/28444290
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6877687/
https://www.ncbi.nlm.nih.gov/pubmed/30535398/
https://www.ncbi.nlm.nih.gov/pubmed/23563705/
https://www.ncbi.nlm.nih.gov/pubmed/29914158/
https://www.ncbi.nlm.nih.gov/pubmed/21831992
https://www.ncbi.nlm.nih.gov/pubmed/18501198/
https://www.ncbi.nlm.nih.gov/pubmed/25592014
https://ro.uow.edu.au/cgi/viewcontent.cgi?article=1053&context=hbspapers
https://www.ncbi.nlm.nih.gov/pubmed/19449378


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