Findings from different studies provide ample evidence to support that a high intake of red and processed meat can be carcinogenic (lead to cancer) and can cause colorectal/colon cancer and other cancers such as breast, lung and bladder cancers. Although red meat has high nutritional value, it is not essential to take beef, pork or lamb as part of a healthy diet to obtain these nutrients, as it can cause obesity which in turn may lead to heart problems and cancer. Replacing red meat with chicken, fish, dairy, mushrooms and plant-based foods may help obtain the required nutrients.
Colorectal cancer is the third most commonly diagnosed cancer and second most common cause of cancer deaths in the world, with more than 1.8 million new cases and approximately 1 million deaths reported in 2018. (GLOBOCAN 2018) It is also the third most commonly occurring cancer in men and the second most commonly occurring cancer in women. There are many risk factors associated with the incidence of different types of cancer including cancer risk mutations, familial history of cancer, advanced age and so on, however, lifestyle also plays a key role in the same. Alcohol, tobacco consumption, smoking and obesity are key factors that can increase the risk of cancers.
Colorectal cancer cases have been continuously increasing globally, especially in the developing countries that are adopting the western style of living. Red meat such as beef, lamb and pork and processed meat such as bacon, ham and hot dogs are a part of the Western diet chosen by developed countries. Hence, this question of whether red meat and processed meat can cause cancer often makes the headlines.
To spice it up, quite recently, “the red meat controversy” had hit the headlines as soon as a study was published in October 2019 in the Annals of Internal Medicine in which the researchers found low evidence that taking red meat or processed meat is harmful. However, the doctors and scientific community strongly criticized this observation. In this blog, we will zoom into the different studies that evaluated the association of red and processed meat with cancer. But before we dig deep into the studies and evidence suggesting the carcinogenic effects, let us quickly glance at some basic details about red and processed meat.
What is Red and Processed Meat?
Any meat that is red before it is cooked is referred to as red meat. It is mostly the meat of mammals, that is usually dark red when raw. Red meat includes beef, pork,lamb, mutton, goat, veal and venison.
Processed meat refers to the meat that is modified in any way to enhance the flavor or extend the shelf life by smoking, curing, salting or adding preservatives. This includes bacon, sausages, hot dogs, salami, ham, pepperoni, canned meat such as corned beef and meat-based sauces.
Being an important part of the Western diet, red meat such as beef, pork and lamb as well as processed meat such as bacon and sausages are highly consumed in the developed countries. However, different studies have shown that high intake of red and processed meat increases obesity and heart problems.
Health Benefits of Red Meat
Red meat is known to have high nutritional value. It is an important source of different macronutrients and micronutrients including:
- Vitamin B12
- Vitamin B3 (Niacin)
- Vitamin B6
- Saturated fats
Including protein as part of a healthy diet is key for supporting our muscle and bone health.
Iron helps in making haemoglobin, a protein that is found in the red blood cells and helps in transporting oxygen in our body.
Zinc is required to maintain a healthy immune system and healing wounds. It also plays an important role in DNA synthesis.
Vitamin B12 is critical for the normal functioning of the brain and the nervous system.
Vitamin B3/Niacin is used by our body to convert the proteins and fats into energy. It also helps to keep our nervous system as well as skin and hair healthy.
Vitamin B6 helps our body to make antibodies that are needed to fight different diseases.
In spite of the fact that red meat has nutritional value, it is not essential to take beef, pork or lamb as part of a healthy diet to obtain these nutrients, as it can cause obesity and increase the risk of heart problems and cancer. Instead, red meat can be replaced with chicken, fish, dairy, mushrooms and plant-based foods.
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Evidences on the Association of Red and Processed Meat with Cancer Risk
Below are some of the recent published studies that evaluated the association of red and processed meat with the risk of colorectal cancer or other cancer types such as breast, lung and bladder cancers.
Association of Red and Processed Meat with Colorectal Cancer Risk
United States and Puerto Rico Sister Study
In a recent analysis published by January 2020, researchers analyzed the association of red and processed meat consumption with the risk of colorectal cancer. For the study, the data of red and processed meat consumption was obtained from 48,704 women aged between 35 to 74 years who were participants of the US and Puerto Rico-based nationwide prospective cohort Sister Study and had a sister diagnosed with breast cancer. During a mean follow-up of 8.7 years, 216 colorectal cancer cases were diagnosed. (Suril S Mehta et al, Cancer Epidemiol Biomarkers Prev., 2020)
In the analysis, it was found that higher daily intake of processed meats and barbecued/grilled red meat products including steaks and hamburgers were associated with an increased risk of colorectal cancer in women. This indicates that red and processed meat may have carcinogenic effects when consumed in high quantities.
Western Dietary Pattern and Colon Cancer Risk
In a study published in June 2018, the dietary pattern data was obtained from Japan Public Health Center-based Prospective Study which included a total of 93,062 participants who were followed from 1995-1998 to the end of 2012. By 2012, 2482 cases of colorectal cancer were newly diagnosed. This data was obtained from a validated food-frequency questionnaire between 1995 and 1998. (Sangah Shin et al, Clin Nutr., 2018)
The western dietary pattern had high intake of meat and processed meat and also included eel, dairy foods, fruit juice, coffee, tea, soft beverages, sauces, and alcohol. The prudent dietary pattern included vegetables, fruit, noodle, potatoes, soy products, mushroom, and seaweed. The traditional dietary pattern included consumption of pickles, seafood, fish, chicken and sake.
The study found that those who followed a prudent dietary pattern showed a reduced risk of colorectal cancer, whereas, women who followed a western dietary pattern with high intake of red meat and processed meat showed a higher risk of colon and distal cancer.
Study done on Jewish and Arab population
In another study published in July 2019, the researchers evaluated the association of different types of red meat intake and risk of colorectal cancer among Jewish and Arab populations in a unique Mediterranean environment. The data was taken from 10,026 participants from The Molecular Epidemiology of Colorectal Cancer study, a population-based study in northern Israel, where the participants were interviewed in-person about their dietary intake and lifestyle using a food-frequency questionnaire. (Walid Saliba et al, Eur J Cancer Prev., 2019)
Based on the analysis of this specific study, the researchers found that the overall red meat consumption was weakly associated with colorectal cancer risk and was significant only for lamb and pork, but not for beef, irrespective of tumor location. The study also found that increased consumption of processed meat was associated with a mild increased risk of colorectal cancer.
Western Dietary Pattern and Quality of Life of Colorectal Cancer Patients
In a study published in Jan 2018, the researchers from Germany evaluated the association between dietary patterns and quality of life changes in colorectal cancer patients. The researchers used data from 192 colorectal cancer patients from the ColoCare Study with quality of life data available before and 12 months post-surgery and food frequency questionnaire data at 12 months post-surgery. The Western dietary pattern evaluated in this study was characterized by high intake of red and processed meat, potatoes, poultry, and cakes. (Biljana Gigic et al, Nutr Cancer., 2018)
The study found that patients who followed a Western diet had lower chances to improve their physical functioning, constipation and diarrhea problems over time compared to those patients who followed a diet loaded with fruits and vegetables and showed improvement in diarrhea problems.
Overall, the researchers concluded that a western dietary pattern (which is loaded with red meat such as beef, pork etc) after surgery is inversely associated with the quality of life of colorectal cancer patients.
Red and Processed Meat intake and Colorectal Cancer Risk In Chinese population
In January 2018, the researchers from China, published a paper highlighting the causes of Colorectal Cancer in China. The data on dietary factors including intake of vegetables and fruits and intake of red and processed meats, were derived from the household survey done in 2000 as part of the Chinese Health and Nutrition Survey which covered 15,648 participants from 9 provinces including 54 counties. (Gu MJ et al, BMC Cancer., 2018)
Based on the survey results, low vegetable intake was the main risk factor for colorectal cancer with a PAF (population attributable fraction) of 17.9% followed by physical inactivity which was responsible for 8.9% of colorectal cancer incidence and mortality.
The third major cause was high red and processed meat intake which accounted for 8.6% of colorectal cancer incidence in China followed by low fruit intake, alcohol drinking, overweight / obesity and smoking which led to 6.4%, 5.4%, 5.3% and 4.9% of colorectal cancer cases, respectively.
Red Meat Intake and Colorectal/Colon Cancer Risk : a Sweden Study
In a study published in July 2017, the researchers from Sweden evaluated the association between intake of red meats, poultry, and fish with incidence of colorectal/colon/rectal cancer. The analysis included dietary data from 16,944 women and 10,987 men from the Malmö Diet and Cancer Study. During 4,28,924 person-years of follow-up, 728 cases of Colorectal Cancer were reported.(Alexandra Vulcan et al, Food & Nutrition Research, 2017)
Following were the key findings of the study:
- High intake of pork (red meat) showed an increased incidence of colorectal cancer as well as colon cancer.
- Beef (also a red meat) intake was inversely associated with colon cancer, however, the study also found that high intake of beef was associated with an increased risk of rectal cancer in men.
- Increased intake of processed meat was associated with an increased risk of colorectal cancer in men.
- Increased consumption of fish was associated with a decreased risk of rectal cancer.
In summary, except for the study done on the Jewish and Arab populations, all other studies do indicate that high intake of different types of red meat such as beef and pork can be carcinogenic and may cause rectal, colon or colorectal cancer depending on the red meat type. Studies also support that high intake of processed meat is associated with an increased risk of colorectal cancer.
Association of Red and Processed Meat with the Risk of Other Cancer Types
Red Meat Consumption and Breast Cancer Risk
In a recent analysis published in April 2020, data on the consumption of different meat categories was obtained from 42,012 participants from the US and Puerto Rico-based nationwide prospective cohort Sister Study who completed a Block 1998 Food Frequency Questionnaire during their enrollment (2003–2009). These participants were women aged between 35 to 74 years old who had no previous diagnosis of breast cancer and are sisters or half-sisters of women diagnosed with breast cancer. During a mean follow-up of 7.6 years, it was found that 1,536 invasive breast cancers were diagnosed at least 1 year post enrollment. (Jamie J Lo et al, Int J Cancer., 2020)
The study found that increased consumption of red meat was associated with an increased risk of invasive breast cancer, indicating its carcinogenic effect. At the same time, the researchers also found that an increased consumption of poultry was associated with a decreased risk of invasive breast cancer.
Red Meat Consumption and Lung Cancer Risk
A meta-analysis published in June 2014 included data from 33 published studies which evaluated the association between red or processed meat consumption and the risk of lung cancer. The data was obtained from literature search carried out in 5 databases including PubMed, Embase, Web of science, the National Knowledge Infrastructure and Wanfang Database until June 31, 2013. (Xiu-Juan Xue et al, Int J Clin Exp Med., 2014)
Dose-response analysis found that for every 120 grams increase of red meat intake per day, the risk of lung cancer increased by 35% and for every 50 grams increase of red meat intake per day the risk of lung cancer increased by 20%. The analysis shows the carcinogenic effect of red meat when taken in high amounts.
Red and Processed Meat Consumption and Bladder Cancer Risk
In a dose–response meta-analysis published in December 2016, the researchers evaluated the association between red and processed meat consumption and bladder cancer risk. The data was obtained from 5 population based studies with 3262 cases and 1,038,787 participants and 8 clinical studies with 7009 cases and 27,240 participants based on literature search in Pubmed database through January 2016. (Alessio Crippa et al, Eur J Nutr., 2018)
The study found that an increase in red meat consumption increased the risk of bladder cancer in the clinical studies but didn’t find any association in the cohort/population based studies. However, it was found that increase in processed meat consumption increased the risk of bladder cancer in both case-control/clinical or cohort/population based studies.
These studies suggest that red and processed meat can have carcinogenic effects and can also cause other types of cancers, apart from colorectal cancer, such as breast, lung and bladder cancers.
Should we completely avoid Red Meat and Processed meat?
All the above studies provide ample evidence to establish that high intake of red and processed meat can be carcinogenic and can lead to colorectal cancer and other cancers such as breast, lung and bladder cancers. Besides cancer, high intake of red and processed meat can also cause obesity and heart problems. But does this mean that one should completely avoid red meat from the diet?
Well, according to the American Institute of Cancer Research, one should limit the intake of red meat including beef, pork and lamb to 3 portions per week which is equivalent to about 350–500g cooked weight. In other words, we should not take more than 50-70g of cooked red meat per day to reduce the risk of colorectal cancer.
Keeping in mind that red meat has nutritional value, for those who cannot avoid red meat, they may consider taking lean cut red meat and avoid the fatty cut steaks and chops.
It is also recommended to avoid processed meats such as bacon, ham, pepperoni,corned beef, jerky, hot dog, sausages and salami as much as possible.
We should try and replace red meat and processed meat with chicken, fish, milk and mushrooms. There are also different plant based foods that can be excellent substitutes for red meat from a nutritional value perspective. These include nuts, leguminous plants, cereals, pulses, spinach and mushrooms.
“What should I eat?” is the most frequently asked question to cancer dieticians and physicians. The right answer depends upon cancer type, underlying genomics, current treatments, any allergies, lifestyle information, and factors like BMI.
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