Mainstream news and social media were alive last week with the release of a new study out of the United Kingdom that links consumption of red meat to higher risk of colorectal cancer. As with past studies linking like this, the headlines painted a grim picture. But the details are more nuanced than coverage makes out.
The study—“Diet and colorectal cancer in UK Biobank”—was published in the International Journal of Epidemiology. Generally, the researchers found that study participants who consumed red meat at the level suggested by the United Kingdom’s (UK’s) National Health Service—70 grams (g), or slightly less than 2.5 ounces a day—had higher risk of colorectal cancer compared to those who consumed less.
“Participants in the highest category of red and processed-meat consumption were consuming an average of 76 g of red and processed meat per day and thus this group was on averaged meeting the current recommendation but still had a 20 percent increase in risk of colorectal cancer comparted with those who ate an average of 21 g [about 0.74 ounces] of red and processed meat per day,” the study authors wrote.
From this, they recommended reductions in government-recommended meat consumption.
The researchers acknowledged that while other studies have been conducted looking at the connection between various food consumption patterns and colorectal cancer, other studies have not had such a large sample size and the data has been older. This study used data collected via the United Kingdom’s “Biobank” dataset, collected on almost 500,000 people in the UK between 2006 and 2010.
“In addition, many of the large previous studies were based on dietary intakes in the 1990s and food-supply data indicate that meat consumption has changed from the 1990s, which a much higher proportion of total meat supply in Europe and the USA now coming from poultry as opposed to beef and pork,” the study authors wrote.
“Thus, it is not certain whether previous risk estimates are relevant to current eating patterns.”
U.S. relevance
Though this study looked at the eating behaviors of people in the UK, the eating patterns it describes have some crossover to the U.S.
The red meat consumption recommendations of the UK’s National Health Service is relatively low compared to similar recommendations in the U.S. The 2015-2020 USDA Dietary Guidelines for Americans suggests adult males get around 6-7 “ounce equivalents” of “protein foods” per day. For adult females, the recommendation is 5-6. Specific recommendations vary by age and sex.
The guidelines also note that the average intake of “protein foods” in adult males in the U.S. is well above the recommended range, whereas the average intake in adult females is at the bottom end of the range.
“Protein foods” are not specifically red meat, but red meat is included in the category, with the guidelines acknowledging that ground beef is a large component of American red meat consumption. There were no definitive recommendations specifically on consumption of red meat, though recommendations call for a shift to more lean, nutrient-dense protein options.
Recent years of World Agricultural Supply and Demand Estimate (WASDE) reports also show an increased domestic availability of red meat per capita in the U.S. In 2017 (most recent complete data), there were 108.4 lbs. of red meat (beef and pork) available per American. This suggests an average possible consumption of over 4.6 ounces of red meat a day per American. This is almost double the “high” level of red meat intake looked at in the study.
Unlike the observation made by the researchers that residents of the UK are eating more poultry rather than red meat, recent WASDE reports suggest that American consumption of all meat is growing, but that the portion of red meat versus poultry is staying relatively steady on average.
For example, in 2017, there were 108.4 pounds of red meat available per person, and 108.7 pounds of poultry available per person. For comparison, in 2007, the availability of red meat was 117.7 pounds per person and poultry was 103.9 pounds. Availability is not a complete description of consumption, but it is often used as an estimate.
Risk vs. incidence
It is important to keep in mind that risk and incidence are not the same thing.
Incidence is the number of times something actually happens in a population; in this case, a diagnosis of colorectal cancer. Risk is the relative likelihood something will happen. Risk is usually discussed in relation to specific activities and their potential impact on incidence; in this case, consuming a certain amount of red and processed meat.
For example, if a population of 100 people collected at random has five people getting colorectal cancer, the incidence is 5 percent on average. If a specific activity increases the risk of colorectal cancer in a population by 20 percent, you would expect the incidence of colorectal cancer in a population of 100 people who all do that activity to be 6 percent (ex. 20 percent of 5 is 1, and 5+1 = 6).
Some coverage of the study has focused on the summarized 20 percent risk increase with red and processed meat, interpreting it as describing incidence.
Methods and other findings
The study utilized self-reported information on food consumption from a large volume of participants—475,581 total participants, 46 percent male and 54 percent female—between the ages of 40-69 at the beginning of the research. Roughly a quarter of the total participants also participated in additional data-gathering efforts (also self-reported) used to verify earlier food consumption reporting.
Participants were tracked for an average of slightly under six years. Over that time, 2,609 cases of colorectal cancer occurred in the study participants (an incidence rate of 0.55 percent over the time).
Researchers additionally found other food consumption patterns correlated with differing risks for colorectal cancer. Alcohol and cheese consumption increased the risk of colorectal cancer at 8 and 9 percent respectively. Regarding alcohol, beer was “associated with an increased risk” relative to other types of alcohol consumed.
Fiber consumption had a negative risk correlation; the more fiber consumed, the larger the decline in colorectal cancer risk.
The researchers additionally found differences between the sexes, with greater consumption of red and processed meat and alcohol in males than females, and greater association with colorectal cancer. There was also a difference in the types of colorectal cancer (defined by polyp location) seen in males versus females.
The researchers concluded their study report with the recommendation “reductions in meat intake below the current recommendation [of the National Health Service] may further reduce the risk of colorectal cancer.” — Kerry Halladay, WLJ editor
