Even 'Moderate' Consumption of Red and Processed Meat Increases Colon Cancer Risk, Study Finds
By Jessica Corbett
For over five years, experts at the University of Oxford, University of Auckland and the cancer research arm of the World Health Organization (WHO) analyzed the diets and cancer rates of people who voluntarily participate in the UK Biobank research project.
The findings, published Wednesday in the International Journal of Epidemiology, align with previous research and subsequent warnings from public health experts about the risks of colon cancer, also known as bowel or colorectal cancer.
"Our results strongly suggest that people who eat red and processed meat four or more times a week have a higher risk of developing bowel cancer than those who eat red and processed meat less than twice a week," said coauthor Tim Key, deputy director of Oxford's cancer epidemiology unit.
"Most previous research looked at people in the 1990s or earlier, and diets have changed significantly since then," Key added, "so our study gives a more up-to-date insight that is relevant to meat consumption today."
The new study showed that people who ate about 76 grams of red and processed meat daily — in line with the UK government's dietary guidelines — had a 20 percent higher chance of developing colon cancer than those who ate only 21 grams per day. Researchers also found that the cancer risk rose by 19 percent for every 25 grams of processed meat — a slice of ham or a rasher of bacon — that people ate daily, and by 18 percent for each 50 grams of red meat — equivalent to a thick slice of roast beef or a lamb cutlet.
The WHO's International Agency for Research on Cancer classified processed meat — which is salted, cured, fermented, smoked or otherwise treated to "enhance flavor or improve preservation" — as carcinogenic to humans in 2015. The U.N. agency also named red meat — including including, beef, veal, pork, lamb, mutton, horse and goat — as a probable carcinogen.
With the new report, "we are not claiming that therefore the [UK] government recommendation is wrong and should be changed," given that other nutritional aspects would need to be considered, Key told The Guardian. "The main message for the public is that it reinforces the government advice that we shouldn't eat large amounts of red and processed meat."
For those looking to cut back on their meat consumption to reduce their cancer risk, lead author Kathryn Bradbury, a senior research fellow at the University of Auckland, said, "you can try having meat free lunches, or days, and swapping red meat for chicken, fish or legumes."
Bradbury's suggestion echoes a January report by the EAT-Lancet Commission that offered a pathway for feeding the world's growing population with the "planetary health diet," which involves cutting red meat consumption by half while doubling the intake of nuts, fruits and vegetables.
The commission also called for a "global agricultural revolution" to overhaul the world's unhealthy and unsustainable food system, which significantly contributes to not only mass malnutrition but also the human-made climate crisis. The EAT-Lancet report followed a series of other studies that have shown that severely scaling back red meat production and consumption is environmentally necessary.
As commission coauthor Tim Lang said when that report was released, "The food we eat and how we produce it determines the health of people and the planet, and we are currently getting this seriously wrong."
Reposted with permission from our media associate Common Dreams.
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By Bob Jacobs
Hanako, a female Asian elephant, lived in a tiny concrete enclosure at Japan's Inokashira Park Zoo for more than 60 years, often in chains, with no stimulation. In the wild, elephants live in herds, with close family ties. Hanako was solitary for the last decade of her life.
Hanako, an Asian elephant kept at Japan's Inokashira Park Zoo; and Kiska, an orca that lives at Marineland Canada. One image depicts Kiska's damaged teeth. Elephants in Japan (left image), Ontario Captive Animal Watch (right image), CC BY-ND
Affecting Health and Altering Behavior<p>It is easy to observe the overall health and psychological consequences of life in captivity for these animals. Many captive elephants suffer from arthritis, obesity or skin problems. Both <a href="https://doi.org/10.11609/JoTT.o2620.1826-36" target="_blank">elephants</a> and orcas often have severe dental problems. Captive orcas are plagued by <a href="https://doi.org/10.1016/j.jveb.2019.05.005" target="_blank">pneumonia, kidney disease, gastrointestinal illnesses and infections</a>.</p><p>Many animals <a href="https://doi.org/10.1016/j.neubiorev.2017.09.010" target="_blank">try to cope</a> with captivity by adopting abnormal behaviors. Some develop "<a href="https://doi.org/10.1016/j.applanim.2017.05.003" target="_blank" rel="noopener noreferrer">stereotypies</a>," which are repetitive, purposeless habits such as constantly bobbing their heads, swaying incessantly or chewing on the bars of their cages. Others, especially big cats, pace their enclosures. Elephants rub or break their tusks.</p>
Changing Brain Structure<p>Neuroscientific research indicates that living in an impoverished, stressful captive environment <a href="https://doi.org/10.1016/j.jveb.2019.05.005" target="_blank" rel="noopener noreferrer">physically damages the brain</a>. These changes have been documented in many <a href="https://doi.org/10.1002/cne.903270108" target="_blank" rel="noopener noreferrer">species</a>, including rodents, rabbits, cats and <a href="https://doi.org/10.1006/nimg.2001.0917" target="_blank" rel="noopener noreferrer">humans</a>.</p><p>Although researchers have directly studied some animal brains, most of what we know comes from observing animal behavior, analyzing stress hormone levels in the blood and applying knowledge gained from a half-century of neuroscience research. Laboratory research also suggests that mammals in a zoo or aquarium have compromised brain function.</p>
This illustration shows differences in the brain's cerebral cortex in animals held in impoverished (captive) and enriched (natural) environments. Impoverishment results in thinning of the cortex, a decreased blood supply, less support for neurons and decreased connectivity among neurons. Arnold B. Scheibel, CC BY-ND<p>Subsisting in confined, barren quarters that lack intellectual stimulation or appropriate social contact seems to <a href="https://doi.org/10.1590/S0001-37652001000200006" target="_blank" rel="noopener noreferrer">thin the cerebral cortex</a> – the part of the brain involved in voluntary movement and higher cognitive function, including memory, planning and decision-making.</p><p>There are other consequences. Capillaries shrink, depriving the brain of the oxygen-rich blood it needs to survive. Neurons become smaller, and their dendrites – the branches that form connections with other neurons – become less complex, impairing communication within the brain. As a result, the cortical neurons in captive animals <a href="https://doi.org/10.1002/cne.901230110" target="_blank">process information less efficiently</a> than those living in <a href="https://doi.org/10.1002/dev.420020208" target="_blank">enriched, more natural environments</a>.</p>
An actual cortical neuron in a wild African elephant living in its natural habitat compared with a hypothesized cortical neuron from a captive elephant. Bob Jacobs, CC BY-ND<p>Brain health is also affected by living in small quarters that <a href="https://doi.org/10.3233/BPL-160040" target="_blank">don't allow for needed exercise</a>. Physical activity increases the flow of blood to the brain, which requires large amounts of oxygen. Exercise increases the production of new connections and <a href="http://dx.doi.org/10.1126/science.aaw2622" target="_blank">enhances cognitive abilities</a>.</p><p>In their native habits these animals must move to survive, covering great distances to forage or find a mate. Elephants typically travel anywhere from <a href="https://www.elephantsforafrica.org/elephant-facts/#:%7E:text=How%20far%20do%20elephants%20walk,km%20on%20a%20daily%20basis." target="_blank">15 to 120 miles per day</a>. In a zoo, they average <a href="https://doi.org/10.1371/journal.pone.0150331" target="_blank" rel="noopener noreferrer">three miles daily</a>, often walking back and forth in small enclosures. One free orca studied in Canada swam <a href="https://doi.org/10.1007/s00300-010-0958-x" target="_blank" rel="noopener noreferrer">up to 156 miles a day</a>; meanwhile, an average orca tank is about 10,000 times smaller than its <a href="https://www.cascadiaresearch.org/projects/killer-whales/using-dtags-study-acoustics-and-behavior-southern" target="_blank" rel="noopener noreferrer">natural home range</a>.</p>
Disrupting Brain Chemistry and Killing Cells<p>Living in enclosures that restrict or prevent normal behavior creates chronic frustration and boredom. In the wild, an animal's stress-response system helps it escape from danger. But captivity traps animals with <a href="https://doi.org/10.1073/pnas.1215502109" target="_blank">almost no control</a> over their environment.</p><p>These situations foster <a href="https://doi.org/10.1037/rev0000033" target="_blank">learned helplessness</a>, negatively impacting the <a href="https://doi.org/10.1155/2016/6391686" target="_blank" rel="noopener noreferrer">hippocampus</a>, which handles memory functions, and the <a href="https://doi.org/10.1016/j.neuropharm.2011.02.024" target="_blank" rel="noopener noreferrer">amygdala</a>, which processes emotions. Prolonged stress <a href="https://doi.org/10.3109/10253899609001092" target="_blank" rel="noopener noreferrer">elevates stress hormones</a> and <a href="https://doi.org/10.1523/JNEUROSCI.10-09-02897.1990" target="_blank" rel="noopener noreferrer">damages or even kills neurons</a> in both brain regions. It also disrupts the <a href="https://doi.org/10.1016/j.neubiorev.2005.03.021" target="_blank" rel="noopener noreferrer">delicate balance of serotonin</a>, a neurotransmitter that stabilizes mood, among other functions.</p><p>In humans, <a href="https://doi.org/10.1006/nimg.2001.0917" target="_blank" rel="noopener noreferrer">deprivation</a> can trigger <a href="https://doi.org/10.3389/fnins.2018.00367" target="_blank" rel="noopener noreferrer">psychiatric issues</a>, including depression, anxiety, <a href="https://doi.org/10.3389/fnins.2018.00367" target="_blank" rel="noopener noreferrer">mood disorders</a> or <a href="https://doi.org/10.1177/1073858409333072" target="_blank" rel="noopener noreferrer">post-traumatic stress disorder</a>. <a href="https://doi.org/10.1007/s00429-010-0288-3" target="_blank" rel="noopener noreferrer">Elephants</a>, <a href="https://doi.org/10.1371/journal.pbio.0050139" target="_blank" rel="noopener noreferrer">orcas</a> and other animals with large brains are likely to react in similar ways to life in a severely stressful environment.</p>
Damaged Wiring<p>Captivity can damage the brain's complex circuitry, including the basal ganglia. This group of neurons communicates with the cerebral cortex along two networks: a direct pathway that enhances movement and behavior, and an indirect pathway that inhibits them.</p><p>The repetitive, <a href="http://dx.doi.org/10.1016/j.bbr.2014.05.057" target="_blank">stereotypic behaviors</a> that many animals adopt in captivity are caused by an imbalance of two neurotransmitters, dopamine and <a href="https://doi.org/10.1016/j.neubiorev.2010.02.004" target="_blank" rel="noopener noreferrer">serotonin</a>. This impairs the indirect pathway's ability to modulate movement, a condition documented in species from chickens, cows, sheep and horses to primates and big cats.</p>
The cerebral cortex, hippocampus and amygdala are physically altered by captivity, along with brain circuitry that involves the basal ganglia. Bob Jacobs, CC BY-ND<p>Evolution has constructed animal brains to be exquisitely responsive to their environment. Those reactions can affect neural function by <a href="https://www.penguinrandomhouse.com/books/311787/behave-by-robert-m-sapolsky/" target="_blank">turning different genes on or off</a>. Living in inappropriate or abusive circumstance alters biochemical processes: It disrupts the synthesis of proteins that build connections between brain cells and the neurotransmitters that facilitate communication among them.</p><p>There is strong evidence that <a href="https://doi.org/10.1523/JNEUROSCI.0577-11.2011" target="_blank">enrichment</a>, social contact and appropriate space in more natural habitats are <a href="https://doi.org/10.1111/j.1748-1090.2003.tb02071.x" target="_blank" rel="noopener noreferrer">necessary</a> for long-lived animals with large brains such as <a href="https://doi.org/10.1371/journal.pone.0152490" target="_blank" rel="noopener noreferrer">elephants</a> and <a href="https://doi.org/10.1080/13880292.2017.1309858" target="_blank" rel="noopener noreferrer">cetaceans</a>. Better conditions <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5543669/" target="_blank" rel="noopener noreferrer">reduce disturbing sterotypical behaviors</a>, improve connections in the brain, and <a href="https://doi.org/10.1038/cdd.2009.193" target="_blank" rel="noopener noreferrer">trigger neurochemical changes</a> that enhance learning and memory.</p>