Could frequent trips to your favorite burger joint increase your cancer risk? According to new research, a diet that is high in processed and red meat may lead to a higher risk of colorectal cancer.

The recently published study gathered information from a large U.S.  prospective cohort of more than 300,000 men and women aged 50-71. Data were gathered through detailed questionnaires and a follow-up period of seven years.

Researchers considered both the type of meat consumed and the cooking methods used. They wanted to look for specific underlying causes of cancer, and they found their culprits in chemistry. It turns out that there are several mechanisms at work. Contributing to the cancer risk are first the type of iron found in red meat (called “heme” iron). Second, nitrates and nitrites, which are preservatives found in processed meat that contribute the “pink” color to hot dogs, cold cuts, bacon and related foods. Finally, HCAs (heterocyclic amines), carcinogenic compounds that develop when meat is cooked at high temperatures.

More than 2,700 diagnoses of colon cancer or rectal cancer were made among participants of this study during its 7-year duration. The conclusion was clear: diets highest in red meat and processed meat were associated with a 24% and 16% higher risk, respectively, for developing these types of cancer compared to diets lowest in these types of meat.  The people with diets lowest in red meat ate an average of 9g per 1,000 calories–or, about 0.6oz of red meat per day assuming a 2,000 calorie per day diet.  Conversely, the people with diets highest in red meat ate an average of 66.5g per 1,000 calories–or, about 4.7 oz red meat per day assuming a 2,000 calorie per day diet.  Furthermore, as red or processed meat intake increased from the lowest levels of intake to higher levels of intake, colorectal cancer risk increased as well.

The researchers found no link between white meat consumption and an elevated cancer risk, possibly due to a difference in total iron content. In looking at dietary impact, it is important to distinguish between the heme iron found in meat, and non-heme iron, which comes primarily from fortified cereals, fruit juice, vegetables, beans and grains. The non-heme iron has not been linked with cancer.

In addition to red meat itself, the study found that cooking at high temperatures (such as in grilling) appeared to add to the danger because of the chemicals that are released during the cooking process. The processing or curing of meats (as with lunch meats and hot dogs) is also a factor, since the procedure typically involves adding nitrate and nitrite substances – chemical preservatives that were linked in this study to an increased cancer risk.

Before this study was done, there had been little evidence regarding the individual elements in a high-meat diet that made it potentially harmful. This latest research supports previously published studies, but goes a step further to identify where the greatest risk is actually coming from.

Cutting back on the amount of red meat and processed meat in your diet is probably advisable based on this latest research.  If you’re not ready to eliminate meat altogether, check out this article on choosing leaner meats in moderation.