Meat Intake And Mortality

This study made headlines last week:

Meat Intake and Mortality, A Prospective Study of Over Half a Million People, Archives of Internal Medicine, Mar 23, 2009

It's conclusion:

"Red and processed meat intakes were associated with modest increases in total mortality, cancer mortality, and cardiovascular disease mortality."

Facts:

• 545,653 (half a million) participants
  
• Aged 50 to 71 at baseline
  
• Followed for 10 years (1995 - 2005)
  
• Meat intake estimated from food frequency questionnaire
  
• Questionnaire collected info over the previous 12 months, completed at baseline
  
• Meat was grouped into "red" (beef and pork), "white" (poultry and fish), and "processed"

For a taste of what food frequency questionnaires are like, go here (pdf) to see the one used in this study.

The coverage the study received (Study: Lots Of Red Meat Increases Mortality Risk, Daily Red Meat Raises Chances Of Dying Early) was a little too enthusiastic, I thought. This study provided evidence that red meat and processed meat each increase risk for mortality. It suggests a hypothesis. It cannot, by nature of its methods, claim that high meat intake results in earlier death.

It does, however, add quite a big data-dump (half-a-million participants, 10 years of follow up) to the growing body of evidence supporting this association.
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Typing

This was interesting:

"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
  
• Have a higher daily intake of energy, total fat, and saturated fat
  
• Tended to have lower education
  
• Tended to have lower physical activity levels
  
• Tended to have lower fruit, vegetable, fiber, and vitamin supplement intakes."

Of course, all those confounders were adjusted for in the final analysis. Red meat intake, independent of those variables, was still associated with mortality.

White Meat Protective?

This was notable:

"When comparing the highest with the lowest quintile of white meat intake, there was an inverse association [except for CVD mortality in men] for total mortality and cancer mortality, as well as all other deaths for both men and women." [Emphasis mine.]

So, there was a presumed protective effect from eating white meat (rather, substituting white for red) - except for men. The more white meat men ate, the greater their risk for heart disease. (White meat included chicken, turkey, and fish.)

The association was really small though, so any protective effect of substituting white for red, if it existed at all, may also be small.

More Fuel

The associations were consistently dose dependant. The more red meat and processed meat eaten (as you moved up the quintiles), the greater the risk for mortality. This boosts the credibility of the association.

Population Attributable Risks (Or How Many Deaths Could Have Been Prevented)

The authors calculated:

"For overall mortality, 11% of deaths in men and 16% of deaths in women could be prevented if people decreased their red meat consumption to the level of intake in the first quintile." (Women could experience an even greater 21% decrease in mortality from heart disease by cutting back.)

What Is It About Meat That Could Raise Mortality Risk?

Possible mechanisms:

• Carcinogens in cooked meat (heterocyclic amines, polycyclic aromatic hydrocarbons)
  
• Carcinogenic N-nitroso compounds (in processed meat)
  
• Iron (increases oxidation damage)
  
• Organic pollutants (pesticides, dioxin, PCB) bioaccumulate in animal fat
  
• Saturated fat (linked to breast and colon cancer)

What Did Meat Groups Say?

The American Meat Institute, the National Pork Board, and the National Cattlemen's Beef Association dismissed the findings.
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