Fact CheckHealth

Is Twitter user’s claim that intake of smoked or grilled food causes colorectal cancer true?

Claim: A Twitter User Femi (@Obaluaye_) claimed that smoked or grilled food contains mutagenic chemicals and cancerous agents that can cause colorectal cancer and damage to the liver and kidney.

There is a causal relationship between grilled or smoked food and colorectal cancer, however, it all depends on the level of one’s consumption. The claim is therefore partially true.

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On November 15, 2021, a Twitter user Femi (@Obaluaye_) claimed that smoked or grilled food contains heterocyclic aromatic amines and other carcinogenic agents that cause colorectal cancer, damage the kidney, damage liver and eventually kill the person.

Screenshot of the post

The post as at November 23, 2021 has garnered over 13.2 thousand likes and 5, 280 comments.

The smoking and grilling of meat, fish and poultry has become increasingly popular as a food preparation method. Historically, the smoking of meat dates back to when people first lived in caves. It was one of the first food preparation techniques.

Fish and meat are a kind of perishable product and if it is not sold or consumed fresh, proper preservation techniques have to be applied to extend its shelf life. And the preservation methods include freezing, drying -sun drying or oven drying, fermentation, heat treatment and smoking.

With the irregular electricity power supply in Nigeria, it has been observed that most people turn to smoking or grilling to preserve their food or sometimes to cook them. Also, smoking or grilling is not only done as a preservative which is the original purpose but also done for the unique taste and flavour conveyed by the smoking method in recent times.

So, is the claim that smoked or grilled food contains heterocyclic aromatic amines and other carcinogenic agents that cause colorectal cancer, damage the kidney, damage liver and eventually kills the person true?

Smoked/grilled food and carcinogenic agents

According to the National Cancer Institute, Heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) are chemicals formed when muscle meat, including beef, pork, fish, or poultry, is cooked using high-temperature methods, such as pan frying or grilling directly over an open flame.

In laboratory experiments, HCAs and PAHs have been found to be mutagenic i.e, they cause changes in DNA that may increase the risk of cancer.

HCAs are formed when amino acids (the building blocks of proteins), sugars, and creatine or creatinine (substances found in muscle) react at high temperatures. PAHs are formed when fat and juices from meat grilled directly over a heated surface or open fire drip onto the surface or fire, causing flames and smoke. The smoke contains PAHs that then adhere to the surface of the meat. PAHs can also be formed during other food preparation processes, such as smoking of meats.

The formation of HCAs and PAHs varies by meat type, cooking method, and range level (rare, medium, or well done). Whatever the type of meat, however, meats cooked at high temperatures, especially above 300 ºF (as in grilling or pan frying), or that are cooked for a long time tend to form more HCAs. For example, well-done, grilled, or barbecued chicken and steak all have high concentrations of HCAs. Cooking methods that expose meat to smoke contribute to PAH formation.

According to the Centers for Disease Control and Prevention (CDC), colorectal cancer is cancer that occurs in the colon or rectum. Sometimes it is called colon cancer, for short. The colon is the large intestine or large bowel. The rectum is the passageway that connects the colon to the anus. Sometimes abnormal growths, called polyps, form in the colon or rectum. Over time, some polyps may turn into cancer. 

Image of the Colon   photo credit: CDC


A consultant oncologist, Dr Okereke Chukwuma, said cooking meat at high temperatures by grilling or frying could potentially elevate the risk of colorectal cancer, but a definite conclusion on this is still up for debate.

He said; “It is true but the person has to be exposed to eating such foods for a long time, and that is not the case in Nigeria. Basically, there is some truth in that claim, but things that have to do with medicine don’t have a straight yes or no answer. When we speak of smoked food for example, there is a strong association between smoked products and cancer of the stomach. Red meat generally-smoked or cooked increases the risk of colon cancer. However, this is in the case of prolonged consumption over a long time.”

He added that although the claim is true, it is still subject to further evaluation.

The Director of the Center for Integrated Research in Cancer and Lifestyle at Cedars-Sinai Medical Center in Los Angeles, Dr. Stephen Freedland, in an article reveals that there is inconsistent data linking the consumption of grilled or smoked meat to cancer.

“Although there is increasing evidence tying the consumption of processed meats, such as hot dogs, with some of the same cancer studies that have been linked to grilled or well-done meat, it may be that individuals who eat a lot of charred steak or well-done burgers are also more likely than the average person to eat a lot of bacon or hot dogs. And so, it could be the processed meat—not the blackened steak—those accounts for any increased cancer risks. Sorting out what’s driving these associations is very hard.’

In another article published by Moffitt Cancer Center, An Epidemiologist, Dr Kathleen Egan, said there is convincing evidence of an association between colorectal cancer risk and higher intakes of red meat, whether grilled or smoked.

“Processed red meats, such as ham, sausages, bacon and hot dogs, undergo treatments like curing, smoking or the use of chemical preservatives and additives to improve shelf life and taste. The problem is those processes introduce N-nitroso compounds, which some studies have found to be linked to cancer risk,” she said.

A study by some researchers revealed that foods containing a significant quantity of red or preserved meats could increase the risk of various cancers, including colorectal cancer. This can be due to a combination of factors such as the content of fat, protein, iron, and/or meat preparation. It further added that red meat may be associated with colorectal cancer by contributing to N-nitroso compound (NOC) exposure.

This is just as another study does not show evidence of increased cancer risk among people who eat a lot of grilled meat. The study further reveals that there is an enhanced association between smoking and colorectal cancer risk which supports a role for NAT2 and tobacco smoke heterocyclic amines in the etiology of colorectal cancer However, the study only provides weak support for a similar association with meat heterocyclic amines.


There is a causal relationship between grilled or smoked food and colorectal cancer; however, it all depends on the level of one’s consumption. Eating grilled or smoked food frequently is probably unwise if one is worried about cancer. But experts say enjoying it occasionally  isn’t something one should stress about.

The researcher produced this fact check article per the Dubawa 2021 Kwame KariKari Fellowship partnership with Crest FM to facilitate the ethos of “truth” in journalism and enhance media literacy in the country.

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