26 March 2009

6 minute read

The report examined answers given to a questionnaire from people in the looked at people in the National Institute of Health's - AARP - formerly the American Association of Retired Persons - Diet and Health study.

The report by Rashmi Sinha, PhD; Amanda J. Cross, PhD; Barry I. Graubard, PhD; Michael F. Leitzmann, MD, DrPH; Arthur Schatzkin, MD, DrPH was published in the Archives of Internal Medicine in the US this month.

The report claims that 617,119 people returned the questionnaire and the researchers say they took into account social and environmental variables such as ethnicity, marital status, education and family history of disease as well as the individual's own consumption and exercise habits and physical attributes.

The people questioned were between 50 and 71 years old.

During the 10 years of follow up the 47,976 of the men died and 23,276 of the women.

"In general, those in the highest quintile of red meat intake tended to consume a slightly lower amount of white meat but a higher amount of processed meat compared with those in the lowest quintile," the report says.

"Subjects who consumed more red meat tended to be married, more likely of non-Hispanic white ethnicity, more likely a current smoker, have a higher body mass index, and have a higher daily intake of energy, total fat, and saturated fat, and they tended to have lower education and physical activity levels and lower fruit, vegetable, fibre, and vitamin supplement intakes."

The researchers said that they examined the total and the cause specific mortality in relation to red meat consumption ands found "modest" increases in risk for total mortality as well as for cancer mortality and cardio vascular disease mortality with higher intakes of red and processed meats in both men and women.

The report says that its strength is in the numbers of people surveyed where other studies have been pooled from different surveys where the questions and protocols varied.

The survey for the Archives of Internal Medicine concedes that "there is some possibility that some residual confounding by smoking may remain" and it adds that because of the profile of the people surveyed, the findings should not be should not be extrapolated to other populations.

The researchers' comment of the findings says: "There are various mechanisms by which meat may be related to mortality. In relation to cancer, meat is a source of several multisite carcinogens, including heterocyclic amines and polycyclic aromatic hydrocarbons, which are both formed during high-temperature cooking of meat, as well as N-nitroso compounds.

"Iron in red meat may increase oxidative damage and increase the formation of N-nitroso compounds.

"Furthermore, meat is a major source of saturated fat, which has been positively associated with breast and colorectal cancer.

"In relation to CVD, elevated blood pressure has been shown to be positively associated with higher intakes of red and processed meat, even though the mechanism is unclear, except that possibly meat may substitute for other beneficial foods such as grains, fruits, or vegetables.

"Mean plasma total cholesterol, low-density lipoprotein cholesterol, very-low-density lipoprotein cholesterol, and triglyceride levels were found to be decreased in subjects who substituted red meat with fish.

"Vegetarians have lower arachidonic, eicosapentaenoic, and docosahexaenoic acid levels and higher linoleate and antioxidant levels in platelet phospholipids; such a biochemical profile may be related to decreased atherogenesis and thrombogenesis."

The survey concludes that: "Red and processed meat intakes, as well as a high-risk meat diet, were associated with a modest increase in risk of total mortality, cancer, and CVD mortality in both men and women. In contrast, high white meat intake and a low-risk meat diet was associated with a small decrease in total and cancer mortality.

"These results complement the recommendations by the American Institute for Cancer Research and the World Cancer Research Fund to reduce red and processed meat intake to decrease cancer incidence.

"Future research should investigate the relation between subtypes of meat and specific causes of mortality."

However, the research has been described as flawed by the American Meat Institute, who said that using self reporting in the questionnaire was unreliable.

AMI Executive Vice President James H. Hodges said "Single studies cannot be used to draw major conclusions."

The AMI said that many papers - including several recently published - reached far different conclusions about the role of meat in the diet which the authors did not acknowledge in their discussion of their own interpretations of the study data:

• A paper published in the March 11 American Journal of Clinical Nutrition found that vegetarians had higher risk of colon cancer than meat eaters.
• A Harvard study involving 725,000 people that examined red and processed meat and colon cancer - the largest of its kind on this topic - concluded that there was no risk between the two (Cho, Smith-Warner, et. al., American Association for Cancer Research 2004 proceedings). Additionally, another report from the same research group, failed to find a protective effect of fruit and vegetables against colorectal cancer in this same population group. They concluded, "Fruit and vegetable intakes were not strongly associated with colon cancer risk overall but may be associated with a lower risk of distal colon cancer." (J Natl Cancer Inst 2007;99:1471-83).
• A new study which appears in this month's peer-reviewed Journal of Nutrition carried out by the University of Illinois and Pennsylvania State University tested the effect of diet and found that a moderate-protein diet can have a significant positive effect on body composition as well as on cardio-vascular disease risk factors such as cholesterol. Subjects on the moderate-protein diet reported that they weren't as interested in snacks or desserts, and they didn't have food cravings.

A spokesman for the British Pig Executive in the UK said that British consumers do not eat the quantities of red meat that the study claims to hold a risk.

"The paper suggests a moderate association between high meat red and processed meat consumption and increased risk of cancer. However, average red meat consumption in the UK is at far lower levels that those cited in the report as increasing risk," he said.

"So there is no need for the vast majority of people to be concerned or to reduce their red meat intake. The group classified as high meat eaters by this study consumed over 300g per day, the average intake in the UK is around 80g per day."

"The group classed as high meat eaters were also more likely to smoke undertake lower levels of physical activity and consume less fruit and vegetables and fibre, all factors that previous studies have suggested increase risk of cancer.

"Red meat contains many vital nutrients, which make a positive contribution to a healthy, balanced diet. In particular, red meat is an important source of dietary iron, known to be lacking in the diets of young children and women. This can lead to anaemia."

Further Reading

	-	Go to our previous news item on this story by clicking here.
	-	You can view the full report by clicking here.

March 2009