The idea that red meat is less healthful than white meat may be generally undisputed; multiple studies link red meat consumption to increased health risks including diabetes, stroke, coronary heart disease, weight gain, certain cancers and all-cause mortality. But what exactly is "red meat?" A precise definition is hard to come by.
Virtually all dietary studies categorize poultry and fish as "white meat" and four-legged land animals such as beef, pork and lamb as "red meat." Yet in culinary or cultural contexts, veal is often considered a white meat and duck or goose may be classified as red. Food scientists point to higher concentration of myglobin and slow-twitch muscle fibers as the primary determinant of red meat; however, the dark meat of chicken or turkey usually has more myoglobin than veal or pork.
Even the U.S. Department of Agriculture seems inconsistent in its explanations. According to an online meat preparation fact sheet on lamb, the amount of myoglobin in the animal's muscle determines its meat color category. In a separate USDA fact sheet on poultry production, ratites (large flightless birds such as emu, ostrich and rhea) are identified as red meat because "the pH of their flesh is similar to beef."
What is it about red meat that is so bad for us? Observational studies can detect a correlation between dietary patterns and health outcomes, but they cannot prove causation, nor can they provide much information about the mechanism by which certain foods, including red meat, may promote or undermine health.
"I suspect that multiple factors contribute to adverse effects of red meat," says Walter Willett, MD, DrPH, chair of the department of nutrition at the Harvard School of Public Health and a primary investigator in both the "Nurses' Health Study II" and the "Health Professionals Follow-up Study," from which many recent red meat associations are drawn.
"High amounts of heme iron, which is absorbed even when we have adequate iron stores, is probably a contributing factor for type 2 diabetes," says Willett. "However, the high amounts of saturated fatty acids and cholesterol are also probably contributing risks of cardiovascular disease, and specific amino acids may also be a factor."
Still, not one of these nutrients is consistent across the meat color categories (see chart). If we suspect that consuming myoglobin (or heme iron, or cholesterol, or fat) might shorten lives, why not collect, analyze and report the data on those nutrients, rather than continue to rely on vague and arbitrary designations like "red" and "white" meat?
Furthermore, according to analysis of data from the "Health Professionals Follow-up Study" and "Nurses' Health Study II," people who eat the most beef, pork and lamb live less healthful lifestyles in general. They tend to exercise less, eat fewer vegetables, are more likely to smoke and less likely to take multivitamins. But given the steady stream of bad press for red meat, should we be surprised that health-conscious people tend to eat less of it? Are they healthier because they eat less red meat, or do they eat less red meat because we keep telling them it's bad for them?
Another factor that looms large and is typically unaccounted for in dietary questionnaires is cooking method. Animal protein of any color cooked at high temperatures or over direct heat produces carcinogenic and atherogenic compounds. Without specifying preparation methods in these studies, it is impossible to distinguish between a char-broiled burger and a slow-braised pot roast.
As new factors of potential research interest are identified, questionnaires are updated with new categories and questions, but the ability to examine longitudinal effects is often limited by the less-specific questions included in the earliest versions.
Meanwhile, when it comes to improving public health, simple messages are usually the most effective. In that spirit, perhaps warning people about the dangers of "red meat" is the simplest way to encourage people to eat fewer burgers (and the fries and sodas that often accompany them), even if the color of the meat is not the primary culprit. But do we run the risk of creating the impression that chicken nuggets are more healthful than pork tenderloin?