Although meat is a good source of protein and vitamin B12, excess intake is a major contributor to human disease. In 2010, a study evaluating meat and health issues carried out by Oxford University health found that eating meat no more than three times a week could prevent 31,000 deaths from heart disease, 9,000 deaths from cancer and 5,000 deaths from stroke a year. The World Cancer Research Fund concluded that if we limited red meat and avoid processed meat, this could save the NHS £1.2 billion in costs each year. In agreement, the former chief scientific officer Sir Liam Donaldson has said that reducing the UK’s consumption of animal products by 30 per cent, by 2030 would prevent 18,000 premature deaths every year. A large European Prospective Investigation of Cancer (EPIC) analysed 25,000 people from Norfolk. There was a significantly higher incidence of colon cancer in those individuals who consumed a higher intake of red meat.
Excess meat shortens life expectancy
Another large study, conducted by the National Cancer Institute of California and published in the Archives of Internal Medicine, examined more than 500,000 middle-aged and elderly Americans. They also found that people with diets high in red meat had an increased risk of premature death from a range of diseases, including cancer. Researchers found that those who consumed more than four ounces of red meat per day were 30 percent more likely to die during the 10 years they were followed in the study. Men who had the highest red meat intake had a 22 percent increased risk of dying from cancer, compared to those who consumed the lowest amount of red meat. Similarly, women who reported the highest amount of red meat consumption had a 20 percent increased risk of dying from cancer, compared to those with the lowest red meat intake.
A further study from the University of Illinois looked at the quality of the meat consumed in relation to the survival after ovarian cancer. Among the 335 women analysied those who ate unhealthy processed meats had a higher chance of their cancer returning after initial treatments had finished and a poorer overall survival. Their definitions of unhealthy meats were largely cheap processed meat products including pork pies, sausages, cheap burgers, processed ham and other meats. On the other hand, there was no increased risk of relapse for those who ate white meats, smaller volumes of good quality red meats or fish. Another study from the World Health Organisation (WHO) also demonstrated that the likelihood of cancer was higher among individuals who eat large quantities of meat but again found that the risk was higher in those who consumed processed varieties. On further analysis, the data from this study, and many others, showed that the meat eaters with a high vegetable and dietary fibre intake only had a moderate increased risk whereas high meat and low vegetable and fibre incurred a particularly high risk of colon cancer.
It is established that cancer in lower in vegetarians. One randomised study 93 volunteers from the USA with early prostate cancer who, opted not to undergo surgery or radiotherapy were randomly assigned to a vegan diet, or standard care. The PSA decreased at twelve months in the intervention group by 4 percent, but increased in the control group by 6 percent. Although this supports changing to a vegan diet the intervention also included daily exercise programme and high polyphenol vegetable and fruit intake so this study was not able to prove that stopping meat the most important factor but it very likely contributed to the positive lifestyle change.
A Taiwanese study showed that people who ate a high intake of polyphenols and fibre in vegetables but also meat and cured fish only had a slightly higher cancer rate than pure vegetarians but meat eaters with a low vegetable intake had a significantly higher cancer risk. This suggests that although cured meats contain carcinogens which can trigger tumour growth, the vegetables and soy contain antioxidants that neutralize these compounds. Other studies have confirmed that people who eat less meat are benefiting from the protective effects of other foods which they eat more of – especially fruits, vegetables, whole grains and legumes found in a vegetarian diet.
How meats are prepared can also affect the risk of their cancer potential. The carcinogen section above how burning or barbecuing meat increases the levels of carcinogens drastically. Even pan-frying meat with a high gas flame may be worse than a lower flame or electricity for raising the levels of carcinogens. Research published in the journal Occupational and Environmental Medicine showed that mutagenic aldehydes and heterocyclic amines, are found in cooking fumes produced during high temperature frying of beefsteak. The hotter gas flames release more harmful chemicals from oil in the cooking process compared to lower heat.
Smoking or curing meats also increases carcinogenic hydrocarbons and nitrosamide levels. Another study of Taiwanese teenagers showed that high intake of cured meats and fish was associated with a 74% higher risk of developing acute leukaemia than children and teens who rarely ate those foods.
How could excess meat be harmful?
Vegetable and fibre exclusion:
Most of the harm causes by excessive meat intake is that it tend to be eaten instead of healthy vegetables and fruit. Anyone who observes dinners at an all-inclusive buffet can see the association between meat eaters and salad dodging. As it is quite filling (satiating), many meat aficionados squeeze out the out the vegetables from their plate. The studies described above highlight how important it is to eat high polyphenol, vitamin and fibre rich foods when meat eating. As rule meat should be to add to enhance the taste of the meal rather being the main component so should be less than a third of the vegetable content.
High saturated fats and cholesterol:
Saturated fats have more energy potential than unsaturated fats so many people regard saturated fats as unhealthier than unsaturated fats but this is not necessarily true. The confusion lies in the fact that most animal fats are saturated and unlike plant oils, these products usually also contain cholesterol. Clinical studies have shown that higher intake of meat saturated fats have a much greater impact on triglyceride and cholesterol levels and heart disease than plant saturated fats.
There is strong evidence that unhealthy fat and calorie excess adds to the risk of developing cancer. Evidence is particularly strong with saturated fat acid, high intakes of which have been associated with a poorer prognosis of cancer. The Health Professionals Study revealed that health professionals who had a high energy and fat intake had an increased risk of advanced prostate cancer, especially in those who presented at a young age or who had a positive family history of cancer. Sheila Bingham of the Medical Research Council, UK, presented data in 2003 to show that women who ate more than 90g of fat a day had twice the risk of developing breast cancer than those eating 40g per day.
On average, humans should eat about 0.75g of protein for each kilogram they weigh, based on the Reference Nutrient Intake (RNI). So, for an average man weighing 75kg that’s about 60g of protein a day and an average woman 50kg a day. This can easily be achieved, even when not eating meat, especially if vegetarians ensure adequate intake of protein rich plants such as soya beans, soy products (tofu), nuts or pulses such as quinoa which contain all the essential amino acids. For example, one cup of quinoa has a 10g, two eggs have nearly 15g, one chicken breast contains on average 25g of protein, 10 shrimps or a portion of fish about 30 g and a quarter of a cup of cottage cheese about 35g.
In reality, most people find it very easy to eat a lot more protein than they need. The 2017 National Diet and Nutrition Survey in the UK estimated that men and women eat about 45-55% more protein than they need each day. There is certainly no benefit to having very high protein intakes, and individuals who require high energy intakes for whatever reason should consider how to increase energy intake without increasing protein intakes excessively. More protein in is needed in people training and exercising hard particularly if they want to build up some muscle mass. It is estimated that someone running, cycling or playing competitive sport would need about 1g /kg of body weight. The academy of Nutrition and Dietetics suggest that bodybuilders require about 1.5g of protein per kilogram, to build muscle mass so for a 95 kg hunk, that’s about 150g a day. Again, this can be achieved with moderate meat and plant protein intake but many reply on protein shakes which can contain 55g per serving. It this case sportsmen have to be careful not to over consume protein.
A high-protein diet, for an extended period, can increase the risk of kidney damage. Eating too much protein can also affect people who already have kidney disease. This is because of the excess nitrogen found in the amino acids that make up proteins. The kidneys have to work harder to get rid of the extra nitrogen and waste products of protein metabolism. The same study found that consuming high amounts of protein led to abnormal markers of kidney function and a more concentrated urine.
Diets that are high in protein and meat may cause calcium loss. This is sometimes associated with poor bone health. A review of several studies evaluating meat consumption and healthfound an association between high levels of protein consumption and poor bone health. Although, this is unlikely to be a problem in people who exercise regularly it may be an issue in sedentary individuals who eat a lot of meat and don’t eat many vegetables.
Many weight loss diets advocate higher meat intake and less carbohydrates. This may help in the short term but can lead to excess protein intake especially in more extreme diets such as Atkin’s. Excess protein is usually stored as fat while the surplus of amino acids is excreted. This can lead to weight gain over time, especially if individuals consume too many calories while trying to increase protein intake. A 2016 study found that weight gain was significantly associated with diets where protein replaced carbohydrates, but not when it replaced fat.
Environmental damage from meat production:
The global environmental damage caused by meat production is leading health problems in humans. In the last ten years mankind has consumed more food than was ever produced, calling for the urgent expansion of agriculture. Virtually all of the productive land globally is being exploited by agriculture with nearly half of this land is cultivated for livestock production, plants grown for animals or waste storage.This precious land is often exploited ineffectively to make meat leading to multiple negative outcomes including contamination and over extraction of water supplies, soil erosion and in an attempt to meet demand, mass scale deforestation. This, coupled with increased contributions to greenhouse gas from livestock and industry, is accelerating the effects on global warming and subsequent climate change leading to flash floods, droughts, damaged habitats and dessert formation. In the UK, damage to our environment is already costing an extra £2.3 billion a year. South Africa is experiencing its worst drought in 100 years causing harvests to fail and food stockpiles to disappear. In Kenya, it has become 4 times more common for periods of devastating drought to occur since records began.In 2015 the consumption of crops by human per day on average was 21 billion pounds in comparison to the per day consumption by livestock which was 135 billion pounds. This is straining the resources of available land and economically grain and plants would go much further if they were eaten directly rather than by livestock. Animal agriculture is the leading cause of species extinction, ocean dead zones, water pollution, nitrogen flooded dead zones in our oceans and habitat destruction. We can make an effort to either stop eating meat or reduce to 2-3 times a week. Choosing quality over quantity with emphasis on grass fed, organic or traditional, preferably local farms.
The chapter on carcinogens has already highlighted the risks of heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs). These chemicals are formed when muscle meat, including beef, pork or poultry, is cooked using high-temperature methods, such as pan frying or grilling directly over an open flame. More specifically HCAs are formed when amino acids, sugars, and creatinine react at high temperatures. PAHs are formed when fat and juices from meat grilled directly over an open fire drip onto the fire, causing flames. These PAH containing flames then adhere to the surface of the meat. PAHs can also be formed during other food preparation processes, such as smoking of meats.The formation of HCAs and PAHs varies by meat type and more likely occur when cooking at high temperatures. HCAs and PAHs are carcinogenic because they are capable of DNA damaging DNA causing mutations. In laboratory animal experiments, high intake has been shown increase the risk of cancer of the breast, colon, liver, skin, lung, prostate and other organs. In human studies have clearly demonstrated a link between high consumption of well done, fried, charred, smoked or barbecued meats with increased risks of colorectal, pancreatic and prostate cancer.
N-nitroso compounds (NOC)including nitrates, nitrites and nitrosamines are described, in detail, in the carcinogen section so will only be summarized again here. Most of our nitrates intake comes from plants which are converted into healthy nitric oxide. In meats, they are found naturally or are added to processed meats as preservatives particularly bacon, ham, salami and other cured meats which lends them their pink coloration. Nitrates themselves are relatively inert, until they are reduced to nitrites and then nitrosamine. Nitrates can turn into nitrites by bacteria in the mouth and then be swallowed. After consumption, depending how they are eaten, what they are eaten with, meat nitrites are either converting into healthy nitric oxide, or volatile nitrosaminessuch as nitrosodimethylamines (NDMA),which are carcinogenic. In the laboratory, most nitrosamines can induce DNA damage causing liver, lung, and stomach cancer. In man, studies suggested they could be implicated in the risk of both childhood and adult brain tumors and colorectal cancers.The UK biobank study found that just processed meat intake equivalent to 2 sausages a week was linked to an increased risk of breast cancer. The WHO and WCRF have issued repeated warnings that nitrite rich processed meats are definite carcinogens.
In some heavily processed meats the nitrites have already been converted in to the volatile nitrosamine called nitrosodimethylamine (NDMA) as a result of direct-fire drying. Likewise, dried, smoked and salted fish have also been found to contain high concentrations of nitrosamines and not surprisingly their regular intake has been associated with higher rates of colon and rectal cancers.Grilling or frying amino acid rich meats at high temperatures can also encourage the conversion of nitrites to nitrosamines. On the other hand, even though vegetables contain nitrates/nitrites, they are rarely exposed to such high heat and are low in amino acids so don’t contain NDMA.Within the body the bacteria in the stomach and gut, the heme ion in red meat, the amount of vitamin c and healthy polyphenols can all affect whether either carcinogenic nitrosamines or healthy nitric oxides are formed and because of their importance they have been summarized again here:
Bacterial overgrowth in the stomach, particularly helicobacter pylorican create an environment conducive for nitrosamine formation, which may explain why chronic infection with these bacteria increases the risk of stomach cancer. People who use proton pump inhibitors, a common class of acid suppressants, may also be more susceptible to nitrites because the diminished acidity in their stomachs encourages bacterial growth. On the other hand, a healthy bacterial flora in the rest of gut reduces the formation of nitrosamines and generally reduces inflammation protecting the mucosa.
Vitamin C and polyphenols in foods including chorophil also directly inhibits nitrosamine formation in foods. This explains why vegetables high in nitrates/nitrites do not increase the cancer risk, in fact quite the opposite; they are associated with a lower cancer risk and have numerous healthy benefits. In an effort to minimize nitrosamine formation, while still preventing food-borne infections, meat manufacturers now add the antioxidant ascorbic acid, or vitamin C, to their products. This also highlights the importance of combining fibre and polyphenol rich fruit and veg with every meat containing meal.
The heme ion in red meat has a catalytic effect on formation of nitrosamines from nitrites. This explains the findings from epidemiological studies reporting a link between red and processed meats and bowel cancer but not with white meats consumption. The heme ion also has other direct carcinogenic propertiesvia the creation of cytotoxic and genotoxic aldehydes caused by lipoperoxidation of unhealthy fats. This explains the induction of colon cancer finding in laboratory rats feed with dietary hemoglobin and red meat even without nitrites.
Meat and health – conclusion
Although the risk of cancer is lower in vegetarians, the evidence would suggest that eating non-red meat in moderation is probably safe provided the diet is otherwise very healthy. There are of course some benefits to eating meat – it is the most easily absorbed source of vitamin B12, protein and iron pre-menopausal women, teenage girls and young children, – all of whom are at high risk of iron deficiency and would benefit from regular meat in their diets. The same applies to adults with cancer if recovering from a period of malnutrition, such as a prolonged period of poor appetite, or a recent operation as, undoubtedly, meat is a good source of protein. A further study also showed that beef reared on grass as free range had good levels of omega 3 particularly those reared organically. A serving of extra-lean good quality meat, less 2-3 times a week may not be harmful.
Summary – 30 tips to aid meat and health:
- If you eat meat go for quality not quantity
- Use meat for its taste, but not as the main content of the meal
- If you eat meat limit to 2-3 times a week rather than every day
- Meat shouldn’t be your main protein, try pulses, quinoa, lentils
- Eat plenty of polyphenol and vitamin c rich foods with every meal.
- There should be three times more vegetables than meat on the plate
- Use plenty of herbs and spices to counterbalance the carcinogens
- When eating meat make sure you also have plenty of fibre
- Avoid cheap meats in tins, sausages, burgers and pies
- Avoid hot dogs, sausage, ham, bacon, pastrami, salami
- Avoid smoked meats
- Reduce intake of heme ion rich red meats such beef, lamb or liver
- Try to go for free range, organic or at least grass feed animals
- Serrano ham and real biltong have lower amounts of nitrites
- Parma ham & prosciutto don’t have added nitrites.
- Particularly avoid barbecued or blackened meats
- Avoiding direct exposure of meat to flame or a hot metal surface
- Avoiding prolonged cooking times (especially at high temperatures).
- Use an oven to partially cook meat prior to grilling or barbecuing.
- Continuously turn or flip meat over on a high heat source.
- Clean the black from frying pan, griddle, hot plate or barbeques
- Remove charred portions of meat
- Refraining from using gravy made from meat dripping
- Avoid direct-fire drying meats, dried salted fish
- Reduce the heat when grilling or frying
- Avoid taking long term anti-indigestion therapies if possible
- Look after your healthy gut bacteria
- Gently grill or casserole rather than fry or burn on the barbeque
- Remove excess fat and skin
- If extra oil is needed use olive oil rather than animal