Research from Loma Linda University Health in California has suggested that consuming small amounts of red or processed meat can increase the risk of death when compared to individuals following a no-meat, vegetarian diet.
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The study included 72,149 individuals participating in the Adventist Health Study-2 (AHS-2), a large cohort study of Seventh-day Adventist men and women in the US and Canada.
Researchers were able to investigate the effects of low-level consumption of red and processed meats compared with the effects of not eating red or processed meat at all, as approximately 50 percent of Adventists follow a vegetarian diet. Those who are not vegetarian typically only eat small amounts of meat.
The health effects of a low meat diet versus a vegetarian diet were previously unknown, explained Saeed Mastour Alshahrani, lead author of the study:
We [wanted] to take a closer look at the association of low intakes of red and processed meat with all-cause, cardiovascular diseases, and cancer mortality compared to those who didn’t eat meat at all.”
According to the study, global meat consumption has increased in developing and developed countries, with red meat being the most commonly consumed meat in the US.
The study also describes links between red and processed meat and cardiovascular disease (CVD), diabetes, and certain types of cancer.
However, it notes that the studies that have produced these links between red and processed meat consumption and the above diseases left the question of whether excluding these meats from the diet would correlate with lower risk of disease incidence “unanswered”.
Red and processed meat has been linked to colorectal cancer
Both red meat and processed meat has been linked to an increased risk of colorectal cancer in particular, with one suggested cause involving haem, a compound that contains iron and provides red meat its color.
Haem can instigate the formation of carcinogenic compounds that damage the bowel lining, possibly leading to bowel cancer. Additionally, processed meat contains nitrites and nitrates that when digested, can form carcinogenic compounds.
Red meat includes beef, veal, pork, lamb, mutton, horse, and goat, and an intake limit has been recommended at three portions a week, equalling to 350-500g cooked weight.
Processed meats include any meat that has been smoked or cured, and meat that has been treated with chemical or salt preservatives. The types of meat classed as processed are bacon, salami, chorizo, corned beef, pepperoni, pastrami, hot dogs, and all types of ham.
Consuming processed meat is not recommended due to strong evidence that it causes colorectal cancer.
Meat-eaters were ‘younger and less educated’
The Adventist Health Study-2 was primarily created to investigate the effects of diet on cancer risk. For this new study, the researchers assessed the cohort’s diet with a food frequency questionnaire, and used the National Death Index for data collection on mortality. Around 90 percent of participants who ate meat only ate up to two ounces of red meat a day.
The study, which was recently published in the journal Nutrients, found that over a mean follow-up period of 11.8 years, 7,961 deaths occurred overall. Of these deaths, 2,598 were from cardiovascular disease, and 1,873 were cancer-related deaths.
When compared with “zero intake subjects”, which describes participants following a vegetarian diet, those with the highest unprocessed red meat intake were “younger, less educated, and less physically active.”
It was also shown that they also had a “higher prevalence of current smoking, alcohol use, and slightly higher BMI.”
Those with high intakes of unprocessed red meat also “tended to have lower intakes of cruciferous vegetables, fruits, whole grains, legumes, and nuts and seeds.” Their intake of eggs, dairy, and unprocessed poultry and processed meat was also higher.
Even small amounts of red and processed meat can be harmful
It was concluded that even diets containing small amounts of red and processed meat are associated with “moderately higher risks of all-cause and CVD mortality”.
However, the study states: “Processed meat alone was not significantly associated with risk of mortality. The combined intake of red and processed meat was associated with all-cause mortality […] and CVD mortality.”
The researchers also state in the study discussion that its results are in contrast to several US cohort studies that found “significant” associations between cancer mortality and red and processed meat consumption, and notes that this could be due to the fact that researchers adjusted for dietary variables including dairy, whole grains and legumes, which have been linked to a reduced risk of certain cancers.
The discussion goes on to explain that the study’s “lack of association for cancer mortality does not necessarily indicate no relationship to cancer incidence,” with vegetarian dietary patterns “not at lower risk of cancer mortality compared with nonvegetarians”, although this study’s particular cohort did suggest a “lower overall cancer incidence”.
Our findings give additional weight to the evidence already suggesting that eating red and processed meat may negatively impact health and lifespan.”
Dr. Michael Orlich, Co-author
Researchers also say that their study was able to fill an “important gap” in literature, in that they were “able to evaluate the association of red and processed meat at low consumption levels compared to zero-intake subjects, whereas other studies have only compared risk at higher intake levels.”
Red and Processed Meat and Mortality in a Low Meat Intake Population. Nutrients. 8 March 2019. 11(3), 622. DOI:10.3390/nu11030622.