Does Meat Cause Cancer?

According to a report released today, processed meat causes bowel (colorectal) cancer. After considering more than 800 studies examining the association between meat and cancer, the World Health Organization’s International Agency for Research on Cancer (IARC) Working Group classified processed meats as Group 1, carcinogenic (cancer causing). Yet the results aren’t as crystal clear as they seem.

What is Red Meat and Processed Meat?

Red meat – unprocessed mammalian muscle meat – beef, pork, veal, lamb, mutton, horse or goat meat, including minced or frozen meat

Processed meat – meat that is transformed through salting, curing, fermenting, smoking or other processes to preserve the meat and enhance flavor. Processed meats can include other meats or meat byproducts such as blood. Hot dogs, sausages, corn beef, beef jerky and canned meat are all examples of processed meat.

Carcinogenic – compounds that are carcinogenic “do not cause cancer at all times, under all circumstances. Some may only cause cancer in people who have a certain genetic makeup. Some of these agents may lead to cancer after only a very small exposure, while others might require intense exposure over many years,” states the American Cancer Society.

What they Found

Processed Meat:
Though they considered 800 studies, their conclusions were drawn upon 18 cohort studies (this is when scientists follow a group of people that don’t have the disease – in this case cancer – over time to see who does and who doesn’t develop cancer). Twelve of the 18 studies reported positive associations between processed meat consumption and colorectal cancer. Six out of 9 case-control studies (where they look at the diet of people with cancer and compare it to the diet of people without cancer) reported a positive association and a meta-analysis (statistical approach to combining results from several studies) of 10 cohort studies reported a statistically significant dose-response relationship with an 18% increase in risk for every 50 gram (1.5 oz. or about the size of ½ of a deck of cards) of processed meat eaten daily. This is relative risk. Your risk goes up 1.18 times. To put this into perspective, if your risk of developing it over the course of a lifetime is 6%. If you eat 1.5 oz. of processed meat daily, your risk will go up to 7%. This is an example, this report doesn’t tell us how likely we are to develop bowel cancer.

Dr. Kurt Straif, Head of the IARC Monographs Programme stated “for an individual, the risk of developing colorectal cancer because of their consumption of processed meat remains small, but this risk increases with the amount of meat consumed.” Recent estimates suggest approximately 34,000 cancer deaths per year can be attributed to diets high in processed meats.

Red Meat:
The Working Group classified red meat as “probably carcinogenic to humans” while stating there is “limited evidence in human beings for the carcinogenicity of the consumption of red meat.” If those two statements sound like they contradict each other, here’s why:

The largest body of data they found was from 14 cohort studies (where they follow a group of people that don’t have the disease – in this case cancer – over time to see who does and who doesn’t develop cancer). Seven of the 14 studies showed higher consumption of red meat (as compared to lower consumption of red meat) was positively associated with colorectal cancer. Seven out of 15 case-control studies (where they look at the diet of people with cancer and compare that to the diet of people without cancer) found higher consumption of red meat was positively associated with colorectal cancer compared to lower intake of red meat. “No association was seen in  several high quality studies.” The author suggests that bias and confounding couldn’t be ruled out (other diet and lifestyle variables may have affected the results.

What Makes Processed Meat Carcinogenic?

When meat, fish, or poultry (chicken, turkey, ducks, geese) are cooked over high temperatures, chemical compounds that are known or suspected carcinogens (cancer causing) including N-nitroso-compounds (NOC), polycyclic aromatic hydrocarbons (PAH), advanced glycation end products (AGEs) and heterocyclic aromatic amines (HCA) are formed. High and dry heat including frying, grilling and barbecuing are the worst combination for the production of these chemicals. The 2-page report mentions some of these compounds as “mechanistic evidence” supporting their conclusions while also stating that we don’t know how cancer risk is increased by processed and red meat. (The full report won’t come out for several months).

N-nitroso-compounds (NOC) are found in nitrate-cured meats, smoked foods (fish or meat), malt in beer and whiskey production, pickled vegetables and foods stored under humidity leading to fungi that generate nitrosamines.

Polycyclic aromatic hydrocarbons (PAH) are formed when fat and juices from meat grilled over an open flame drip onto the fire, resulting in flames, and PAHs adhering to the surface of the meat. Smoking meats also leads to the formation of PAHs. PAHs are also found in air pollution.

Advanced glycation end products (AGEs) are harmful compounds formed during dry heat cooking. Though many foods contain AGEs, meats fried or cooked over dry heat have significantly more AGEs than any other food. AGEs accumulate in the human body, affect cell functioning and may contribute to insulin resistance, type 2 diabetes and, as the name implies, aging.

Heterocyclic aromatic amines (HCA) are formed when amino acids, sugars and creatine react at high temperatures. When meat, fish, pork and poultry are cooked at higher temperatures for a longer period of time, more HCAs are formed.

HCAs and PAHs must be metabolized by specific enzymes (a process called bioactivation) before they can damage DNA. Yet the activity of these enzymes varies between people and therefore, one’s risk of developing cancer due to HCA and PAH exposure depends on how they metabolize these compounds.

What this Report Does Not Tell Us

IARC Working Groups examine if exposure to a specific food or compound could cause cancer but does not tell us how likely we are to get cancer. Also, there are many known human carcinogens (UV light – including the UV light in those LEDs lights used to set gel nails, alcohol, the mineral oil you use on wood cutting boards and more) – some many cause cancer after little exposure while others take a lifetime of exposure. Many factors influence the development of cancer including age, gender, family history, and other lifestyle factors (tobacco and alcohol use, weight, diet, physical activity).

How Much Processed & Red Meat is Too Much?

Cancer is a complex disease and no single food causes, cures or prevents cancer. However, as stated by the American Institute for Cancer Research (AICR):

  • A modest amount of red meat does not raise colorectal cancer risk.
  • Eating more than 18 ounces of cooked red meat per week increases the risk of  colorectal cancer.
  • Eating small amounts of processed meat regularly increases risk (of colorectal cancer).

AICR recommends avoiding processed meats and eating no more than 18 ounces of red meat per week (3 oz. = about the amount in a deck of cards). I also suggest making potentially better choices (see the infographic below and the 2nd to last paragraph of this blog post). What about HCAs, PAHs and other compounds? Here’s how you can decrease your intake of these compounds:

cooking meat
Where does meat processed without nitrates fit in? We don’t know. If they are processed without nitrates then they should  presumably contain few to no NOCs making them a better choice than meats processed with nitrates. However, I couldn’t find a single study comparing the compounds in meats produced without nitrates to their counterparts produced with nitrates.

If you aren’t preparing your food at home, take a close look at how it was prepared and cooked so you can minimize your intake of these compounds. If you don’t plan on cutting out processed meats, at the very least, limit your intake of sausage, ham, bacon, hot dogs, pepperoni, pastrami, bologna, corned beef, deli/luncheon meats, salami, nitrite-treated meat or meat products as well as meat preserved by smoking, curing or salting, all of which could increase your risk of cancer.

For more information on colorectal cancer, see colorectal cancer stat facts and factors influencing colorectal cancer risk.

Disclosures: None, I have no connection to any red meat commodity boards, stock in red or processed meat companies (though I should look up the shorts or consider buying on a dip) or emotional connection to cows, pigs, horses, red or processed meats 🙂

References:
National Cancer Institute. 
American Institute for Cancer Research
Medline Plus.
Nutr Cancer 2008;60(2):131–144.
J Food Sci 2008;73(6):T100-5.
Cancer Sci 2010;101(2):508-16.
Cancer Epidemiol Biomarkers Prev 2012;21(6):905-15.
Int J Cancer 2014;134(1):125-35.
J Am Diet Assoc 2010;110(6):911-16.
Curr Diab Rep 2014;14(1):453.
Ann N Y Acad Sci 2005;1043:533-44.

Which Fat is Best for Heart Health?

Butter

If you are more confused than ever about dietary fats, you’re not alone. Can a high fat diet help you lose body fat? Which fat is best for heart health – butter, coconut oil or vegetable oil?

What is Cholesterol & Why is it Essential?
Cholesterol is an essential component of all cell membranes and a precursor to hormones, vitamin D and bile acids (needed for the digestion of fat). It is so important that your body regulates cholesterol balance to ensure your cells receive a continuous supply of cholesterol.

How does High LDL Contribute to Cardiovascular Disease?

Though cholesterol is critical for life, low density lipoprotein cholesterol, LDL cholesterol, is considered a risk factor for heart disease because excess LDL can lead to an increase in plaque buildup in your arteries. Think of this process like a garden hose with gunk stuck in it. The gunk interferes with water flowing through the hose. If too much debris gets in there, no water will flow through.  Likewise, plaque in your arteries will decrease the amount of blood that moves through your arteries at one time and a complete blockage could lead to a heart attack or stroke.  Now, this is a simplistic view, especially considering LDL isn’t just one particle but instead, several that contain different amounts of cholesterol. Some research suggests that smaller, more dense LDL particles are more artery clogging. However, in addition to particle size, total number of LDL particles and oxidation of LDL contribute to the disease process.

As LDL particles travel through the bloodstream, excess LDL particles can stick to artery walls (particularly walls that are damaged due to smoking, high blood pressure and other insults). Trapped LDL becomes oxidized and sets off an inflammatory cascade resulting in the development of plaque (gunk) stuck to arteries – atherosclerosis.

Coronary Artery Disease

How Can I Lower my LDL Cholesterol?

Cholesterol in food has little effect on your blood cholesterol.

Years ago we were told to stay away from shrimp, eggs and other high cholesterol foods. Yet this advice wasn’t based on sound science – cholesterol in food has little effect on your blood cholesterol levels. So there is no need to take these nutrient-rich foods out of your diet. Shrimp is loaded with protein, and is a good source of iron plus it contains just 80 calories per serving. Eggs are also packed with nutrition – the whites are an excellent source of protein and the yellow color you see in the yolk is from antioxidants – plant compounds that protect plants from disease and protect your body from the damaging effects of free radicals, compounds that are essential but can cause damage as well.

Coconut Oil, Butter and Other Solid Fats are Not the Best Options

Man-made trans fats (partially hydrogenated oils) are the worst kind of fat you can eat. However, they should, finally, be making their way out of our food supply over the next few years. High levels of *saturated fat, the kind that is solid at room temperature like butter, increases HDL (the “good” cholesterol but not a target of therapy – doctors don’t focus on HDL levels because increasing HDL does not lower heart disease risk) and LDL cholesterol in the blood. In controlled diet experiments where saturated fat is replaced with polyunsaturated fat rich vegetable oils, risk of heart disease is reduced. Replacing saturated fat with monounsaturated fat, the kind found in olive oil, also lowers LDL but not to the extent that polyunsaturated fat does.

Coconut oil is popular and calorie for calorie it might be better for weight management than other fats. However, coconut oil raises our total, good and bad cholesterol levels. And therefore, it is not the best option for heart health.

Excess Carbohydrate Intake can Increase LDL

Overconsumption of carbohydrate-rich foods can also increase VLDL cholesterol (very low density lipoprotein). Foods with added sugars, in particular, are potent stimulators of VLDL production when the energy (calories) aren’t needed right away for energy or increasing glycogen stores (stored carbohydrate in your liver and muscle).

Best Fats for Your Heart

Nuts, seeds, avocados, olives and liquid oils are your bets for heart health. Oils with more polyunsaturated fat have a greater impact on LDL cholesterol than those rich in monounsaturated fat. Make sure you are choosing the right oil for the right cooking application. Many oils can’t stand high heat and they break down, damaging the structure (and function) of the oil.

Fatty Acids in Oils

Conclusion

Many factors contribute to high blood cholesterol levels, including genetics, overweight/obesity, inactivity, smoking, diabetes and age, making cholesterol management a multifactorial issue. Saturated fat increases LDL cholesterol but, as I’ll say over and over, we are all different and, people vary in their response to dietary saturated fat due to intrinsic differences in fat metabolism as well as other factors including obesity, insulin resistance and high triglycerides.

Replace fats that raise cholesterol with liquid oils, nuts, seeds, avocados, and olives. Consider your overall diet as well. Eat a plant-based diet including vegetables (non-starchy veggies as well as beans, lentils and peas), fruits, nuts, seeds and whole grains (oats, barley etc.). Consume fatty fish ( salmon, mackerel, herring, halibut, sardines etc.) at least two times per week. Limit your intake of foods with added sugars and refined starches as well as your alcohol consumption. 

* There are differences in specific saturated fatty acids and their effects on blood cholesterol. Therefore, some foods high in saturated fat do not raise LDL cholesterol. Also, oils have a different array of vitamins (primarily vitamin E) and plant-based compounds that may be beneficial for heart health.

Fatty acids composition of oils taken from the USDA Nutrient Database.