Intake of red meat in the U.S. has fallen dramatically over the past 4 decades.
Red meat is defined as any meat that comes from mammalian muscle. This includes beef, lamb, pork, goat, veal, and mutton.
For many households, red meat is considered a food staple, with some of us consuming beef, lamb, and pork in different variations on a daily basis.
Last year, the average person in the United States is estimated to have consumed around 106.6 pounds of red meat. Although this might appear a high intake, it is a significant reduction from the average 145.8 pounds consumed per capita in 1970.
Over the past 10 years alone, red meat consumption has fallen by around 10 pounds per person, with 2014 seeing the lowest intake of red meat since 1960, at just 101.7 pounds per person.
But why are so many of us cutting down on red meat?
A shift toward plant-based foods
According to a 2016 Harris Poll, approximately 8 million adults in the U.S. are vegetarian or vegan, with concerns about animal welfare being the driving factor.
However, it seems that millions more of us are opting for plant-based foods over meat-based products because we believe that they are more healthful. The 2016 Harris Poll found that 37 percent of U.S. adults "always" or "sometimes" eat vegetarian meals when eating out, with 36 percent of these citing health reasons for their choice.
A number of studies have suggested that when it comes to health, a plant-based diet is the way to go. In December 2016, a position paper from the Academy of Nutrition and Dietetics claimed that a plant-based diet can lower the risk of type 2 diabetes by 62 percent, as well as reduce the risk of heart attack and stroke.
"If you could bottle up a plant-based prescription, it would become a blockbuster drug overnight," commented paper co-author Susan Levin, of the Physicians Committee for Responsible Medicine in Washington, D.C.
It is not only the health benefits associated with plant-based diets that are steering us away from red meat, however, but the health risks that might arise from eating red meat. We take a look at what some of these risks are.
When it comes to red meat intake, cancer is perhaps the most well-established health implication.
In October 2015, the World Health Organization (WHO) published a report concluding that red meat is "probably carcinogenic to humans," meaning that there is some evidence that it can increase the risk of cancer.
Additionally, the WHO concluded that processed meats - defined as "meat that has been transformed through salting, curing, fermentation, smoking, or other processes to enhance flavor or improve preservation" - is "carcinogenic to humans," meaning that there is sufficient evidence that processed meat intake increases cancer risk.
A high intake of processed meat is associated with a greater risk of colorectal cancer, according to the WHO.
To reach these conclusions, the WHO's International Agency for Research on Cancer (IARC) Working Group reviewed more than 800 studies assessing the effects of red and processed meats on various types of cancer.
They found that each 50-gram portion of processed meat - which primarily includes pork or beef - consumed daily increases the risk of colorectal cancer by 18 percent.
The IARC also uncovered evidence of a link between red meat intake and increased risk of colorectal, pancreatic, and prostate cancers.
It is thought that cooking red meats at high temperatures - through frying or barbecuing, for example - is what contributes to an increased cancer risk.
According to the National Cancer Institute - a part of the National Institutes of Health (NIH) - cooking meats at high temperatures can lead to the production of heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs), which are chemicals that have been shown to increase cancer risk in animal models.
However, the report from WHO concluded that the role of HCAs and PAHs in human cancer risk is not fully understood, and from their review, there was not enough data to determine whether the way meat is cooked influences cancer risk.
Kidney failure - whereby the kidneys are no longer able to filter waste products and water from the blood - is estimated to affect more than 661,000 people in the U.S.
Published in the Journal of the American Society of Nephrology, the study reported a dose-dependent link between red meat consumption and risk of kidney failure. For example, participants who were in the highest 25 percent of red meat intake were found to have a 40 percent increased risk of kidney failure, compared with those in the lowest 25 percent.
"Our findings suggest that these individuals can still maintain protein intake but consider switching to plant-based sources; however, if they still choose to eat meat, fish/shellfish and poultry are better alternatives to red meat," says study co-author Dr. Woon-Puay Koh, of the Duke-NUS Medical School in Singapore.
An unhealthful diet, high in saturated fat and cholesterol, is a well-known risk factor for heart disease. A number of studies have suggested that red meat falls into that category, raising the risk of heart disease and other cardiovascular conditions.
Some studies have associated red meat consumption with heart disease.
A 2014 study of more than 37,000 men from Sweden, for example, found that men who consumed more than 75 grams of processed red meat per day were at a 1.28 times greater risk of heart failure than those who consumed under 25 grams daily.
Another study, published in 2013, reported an association between red meat intake and increased risk of heart disease, but this link was not attributed to the high saturated fat and cholesterol content of red meat.
The researchers, from Columbia University in New York, found that gut bacteria digest a compound in red meat called L-carnitine, converting it into a compound called trimethylamine-N-oxide (TMAO).
In mice, the researchers found that TMAO led to the development of atherosclerosis - a condition characterized by the buildup of fatty substances in the arteries, which can lead to heart attack and stroke.
Although there are numerous studies linking red meat intake to poor heart health, other research challenges this association.
A recent study by researchers from Purdue University in West Lafayette, IN, for example, found that eating 3 ounces of red meat three times weekly did not lead to an increase in risk factors for cardiovascular disease.
This inflammation can lead to a number of severe complications, including abscesses, perforation of the colon, and peritonitis (infection and swelling in the lining of the abdomen).
Earlier this month, a study published in the journal Gut suggested that eating high amounts of red meat may also increase the likelihood of developing diverticulitis.
Compared with men who reported eating low quantities of red meat, those who reported eating the highest quantities were found to have a 58 percent greater risk of developing diverticulitis.
The risk was strongest with a high intake of unprocessed red meat, the researchers found.
How much red meat should we eat?
Despite overwhelming evidence of the potential health risks of red meat intake, it is important to note that red meat is full of nutrients.
Red meat is also high in heme-iron - which is absorbed better than plant-derived iron - vitamin B-6, selenium, and other vitamins and minerals.
Still, based on the evidence to date, public health guidelines recommend limiting red meat consumption.
The American Institute for Cancer Research, for example, recommend eating no more than 18 ounces of cooked red meats each week to reduce cancer risk, while processed meats should be avoided completely.
However, while the 2015-2020 Dietary Guidelines for Americans recommend cutting back on red meat intake, they do not specify a daily limit.
According to Dr. Christopher Wild, director of the IARC, the 2015 report linking red meat intake to increased cancer risk supports public health recommendations to limit the consumption of red meat.
However, he notes that red meat has nutritional value, and that this should be considered in future research "in order to balance the risks and benefits of eating red meat and processed meat and to provide the best possible dietary recommendations."