Commonly, especially in gastronomy, red meat or dark meat is red when raw and dark in color when cooked, in contrast to white meat, which is pale in color before and after cooking. This definition only refers to flesh from mammals or fowl.
In nutritional science, red meat is defined as any meat that has more myoglobin than white meat, white meat being defined as non-dark meat from chicken (excluding leg or thigh), or fish. Some meat, such as pork, is red meat using the nutritional definition, and white meat using the common definition.
According to the USDA, all meats obtained from mammals (regardless of cut or age) are red meats because they contain more myoglobin than fish or white meat (but not necessarily dark meat) from chicken.
The culinary definition has many rules and exceptions. Generally meat from mammals (for example cattle, horse meat, bull meat) and meat from hunting (wild boars, deer, pigeons, partridges, quail and pheasant) excluding fish and insects are considered red meat. Although poultry is usually considered white, duck and goose are red. For some animals the culinary definition of red meat differs by cut, and sometimes by the age of the animal is when it was slaughtered. Pork is considered red if the animal is adult, but white if young (e.g. suckling pig). The same applies to young lamb and veal. Game is sometimes put in a separate category altogether. (French: viandes noires — "dark meats".)
Pork is considered white under the culinary definition, but red in nutritional studies. The National Pork Board has positioned it as "Pork. The Other White Meat", profiting from the ambiguity to suggest that pork has the nutritional properties of white meat, which is considered more healthful.
Red meat contains large amounts of iron, creatine, minerals such as zinc and phosphorus, and B-vitamins: (niacin, vitamin B12, thiamin and riboflavin). Red meat is a source of lipoic acid.
Red meat contains small amounts of vitamin D. The liver contains much higher quantities than other parts of the animal.
The accompanying website for the 2005 edition of the USDA food guide pyramid, MyPyramid stated that "fish, nuts, and seeds contain healthy oils, so choose these foods frequently instead of meat or poultry" and for people who wanted to eat meat, it recommended lean or low-fat red meat and poultry. In 2011, the USDA launched MyPlate, which didn't distinguish between kinds of meat, but did recommend eating at least 8 oz of fish each week. In 2011, the Harvard School of Public Health launched the Healthy Eating Plate because of the perceived inadequacies of the USDA's recommendations and presentation. The Healthy Eating Plate encourages consumers to limit red meat and avoid processed meat, and to instead choose fish, poultry, beans or nuts. Its website says: "Eating a lot of red meat and processed meat has been linked to increased risk of heart disease, diabetes, and colon cancer. So it’s best to avoid processed meat, and to limit red meat to no more than twice a week. Switching to fish, chicken, nuts, or beans in place of red meat and processed meat can improve cholesterol levels and can lower the risk of heart disease and diabetes.
Red meat is not a uniform product; its health effects can vary based on fat content, processing and preparation. Processed red meat is linked to higher mortality, mainly due to cardiovascular diseases and cancer. There is some evidence too that the consumption of unprocessed red meat may have negative health effects in humans.
A 2016 literature review reported that for 100g or more per day of red meat consumed, the risk increased 11% for each of stroke and for breast cancer, 15% for cardiovascular mortality, 17% for colorectal cancer, and 19% for advanced prostate cancer.
In 2015 the International Agency for Research on Cancer concluded that red meat is probably (Group 2A) carcinogenic to humans, reported that for each additional 100g (up to a maximum of approximately 140g) of red meat consumed per day, the risk of colorectal cancer increased by 17%; there also appeared to be increased of pancreatic cancer and prostate cancer but the association was not as clear. Put in perspective, in the UK, 56 out of 1000 people who eat the lowest amount of red meat will develop colorectal cancer (5.6%) while 66 out of 1000 high-red meat eaters will develop colorectal cancer (6.6%) (1.17 x 5.6 = 6.6).
A 2013 meta-analysis found an increased risk of gastric cancer with higher consumption of red or processed meat. Red meat itself contains certain factors that, under certain conditions, produce carcinogens like N-nitroso compounds (NOCs).
The consensus on the role of red meat consumption to increased risk of cardiovascular diseases has changed in recent years. Studies that differentiate between processed and fresh red meat have failed to find a link between unprocessed red meat consumption and heart disease. A major Harvard University meta-study in 2010 involving over one million people who ate meat found that only processed meat had an adverse risk in relation to coronary heart disease (CHD). The study suggests that the "differences in salt and preservatives, rather than fats, might explain the higher risk of heart disease and diabetes seen with processed meats, but not with unprocessed red meats." Some mechanisms that have been suggested for why red meat consumption might be risk factor for cardiovascular disease include: its impact on serum cholesterol, that red meat contains arachidonic acid, heme iron, homocysteine, and its high saturated fat content.
Several studies have found a correlation between unprocessed red meat and the occurrence of CHD and certain types of stroke and have controlled for various confounding risk factors. A study of 84,000 women, over a period of 26 years, finds that those with the highest intake of unprocessed red meat, have a 13% increased risk of CHD. Likewise a Harvard study published in 2012, studying mortality as a result of processed and unprocessed red meat consumption finds that one serving of either type of meat a day results in an increased risk of mortality of 13%, while this ratio is indicative of cancer and cardiovascular (CVD) disease, the study indicates that of the 23,926 deaths investigated during the course of the study, 5910 of them were related to CVD and there was no statistical significance between the risk of unprocessed and processed red meats factors in the occurrence of CVD. The disparity between metadata studies definitely need to be addressed, because while one points toward unprocessed red meat being insignificant in certain health risks, there are still correlations to be found in focused large cohort studies.
Unprocessed red meat intake is tentatively associated with an increased risk of type II diabetes, but the link is weaker and less certain than the link between processed red meat and diabetes. Other findings have suggested that the association may be due to saturated fat, trans fat and dietary cholesterol, rather than red meat per se. One study estimated that “substitutions of one serving of nuts, low-fat dairy, and whole grains per day for one serving of red meat per day were associated with a 16–35% lower risk of type 2 diabetes”.
In its Press Release 240 (16 Oct. 2015) the International Agency for Research on Cancer, based on a review of 800 studies over 20 years, defines processed meat as follows: "Processed meat refers to meat that has been transformed through salting, curing, fermentation, smoking, or other processes to enhance flavour or improve preservation. Most processed meats contain pork or beef, but processed meats may also contain other red meats, poultry, offal, or meat by-products such as blood." In 2015 the IARC concluded that processed meat is definitely carcinogenic (Group 1) and found that for each additional 50g of processed meat consumed per day, the risk of colorectal cancer increased by 18% (up to a maximum of approximately 140g); it also found that there appeared to be an increase in gastric cancer but this was not as clear. Nitrates and nitrites found in processed meat (e.g. bacon, ham, salami, pepperoni, hot dogs, and some sausages) can be converted by the human body into nitrosamines that can be carcinogenic, causing mutation in the colorectal cell line, thereby causing tumorigenesis and eventually leading to cancer.
A 2016 literature review found that for the each additional 50g per day of processed meat (e.g., bacon, ham, hot dogs, sausages) consumed, the risk increased 4% for total prostate cancer, 8% for cancer mortality, 9% for breast cancer, 18% for colorectal cancer, 19% for pancreatic cancer, 13% for stroke, 24% for cardiovascular mortality and 32% for diabetes.
Cooking any meat at high temperature and smoking produces the carcinogens polycyclic aromatic hydrocarbon compounds (PAHs) and heterocyclic amines (HCA). The subgroups of heterocyclic amines compounds are Amino-dimethylimidazo-Quinoxaline (MelQx), Amino-Dimethylimidazo-Quinoxaline (DiMelQx), and Amino-methyl-phenylimidazo-pyridine (PhIP), which are mostly formed during cooking meat at high temperatures.Benzo[a]pyrene (B[a]P) is another compound found in meat cooked in extremely high temperatures-this aromatic hydrocarbon is normally found in coal tar, wood burning, or automobile exhaust fumes. According to a study, there was 36% of the MeIQx and 50% of DiMeIQx was present in the well-done barbecued steak; contrary, 20% of PhIP was present in medium-done barbecued steak. Likely because of these factors, marinating fresh lean red meat and thoroughly cooking the meat at low temperature will reduce the production of carcinogenic compounds and thereby lower the risk of colorectal cancer.