May 20, 2010 â?? The first study to systematically separate out the effects of red unprocessed meat from processed-meat products has shown that eating the former is not associated with an increased risk of coronary heart disease or diabetes .
But eating 50 g of processed meat per day--the equivalent of one typical hot dog in the US, or two slices of deli meat--was associated with a 42% higher risk of CHD and a 19% increased risk of diabetes, say Dr Renata Micha (Harvard School of Public Health, Boston, MA) and colleagues in their paper published online May 17, 2010 in Circulation.
Micha explained that US dietary guidelines recommend eating less red and processed meat, but that these are largely based on the expected effects of saturated fat and dietary cholesterol in the meats. However, previous studies, which have generally evaluated red meats together with processed meats, have shown mixed results in terms of the risk of cardiovascular disease and diabetes, she says.
"We found red meats and processed meats had similar amounts of saturated fat and cholesterol, but processed meats had about four times the amount of sodium and 50% more preservatives, such as nitrates, than the unprocessed red meat," she told heartwire . "We suggest that salt and other preservatives might explain this higher risk we found for processed meats."
Not a License to Gorge on Red Meat; Eat Fruits, Vegetables, and Fish
However, Micha emphasized that people "shouldn't use these findings as license to eat as much unprocessed red meat as they like," because although there was no increased risk for heart disease and diabetes, "it is important to stress that there was no reduced risk either." Also, she noted, processed and unprocessed meats have been associated with a higher risk of some cancers, especially colorectal, "and it will be important to evaluate unprocessed meat separately from processed meat for cancer outcomes too," she said.
"People should definitely give more emphasis to increasing consumption of foods that have been shown to be protective, such as fruits, vegetables, whole grains, fish, and nuts," she stressed.
"This paper represents very important work," says Dr Nathan Wong (University of California, Irvine), president of the American Society for Preventive Cardiology, who was not involved with this study.
"The substantial increase in risk of both heart disease and diabetes associated with processed meats, while not surprising, should reinforce the message that these foods, which are particularly high in sodium, other additives, and fat, are potentially harmful and should be minimized or avoided," he told heartwire .
Processed and Unprocessed Meats Should Be Studied Separately
Micha and colleagues reviewed and combined all prior published studies around the world that examined the relationship between eating meat and the risk of heart disease, diabetes, and stroke. They identified 20 relevant studies, including around one million adults in 10 countries, across four continents.
Micha explained that they contacted the authors of each study and requested that they separate out unprocessed from processed meats. After multivariate adjustment, red-meat intake of 100 g per day--defined as unprocessed beef, pork, or lamb--was not associated with CHD (four studies) or diabetes mellitus (five studies).
In contrast, consumption of processed meat--any meat preserved by smoking, curing, or salting, such as sausages, bacon, and salami--was associated with increased risk of CHD (five studies: relative risk per 50-g serving per day=1.42; p=0.04) and diabetes (seven studies: relative risk per 50-g serving per day=1.19; p<0.001). Consumption of red and processed meat was not associated with stroke, but only three studies evaluated these relationships, the researchers note.
"When you tease [the data on] these meats out, you see different associations for disease risk between processed and unprocessed meats," Micha told heartwire . These findings suggest that these types of meats should be studied separately in future research for health effects, she noted.
And although she says cause and effect cannot be proven by these types of long-term observational studies, she explains there is "biological plausibility" for the salt and preservatives in processed meat contributing to the risks observed.
"We know that dietary sodium increases blood pressure, and in animal experiments, nitrate preservatives have been shown to promote atherosclerosis and reduce glucose tolerance. People should definitely avoid eating too much processed meat," she concluded.
Wong agrees: "With a 42% higher risk associated with each 50-g (<2-oz) intake of processed meat, this translates to nearly a doubling of risk for a daily intake of only a quarter of a pound [113.4 g], which many Americans do not think twice about consuming in a single meal," he told heartwire .
The authors report that they have no conflicts of interest. Wong reports no conflicts of interest.
Micha R, Wallace SK, and Mozaffarian D. Red and processed meat consumption and risk of incidence coronary heart disease, stroke and diabetes mellitus. A systematic review and meta-analysis. Circulation 2010; DOI:10.1161/CIRCULATIONAHA.109.924977. Available at: http://circ.ahajournals.org.