New research from the Harvard School of Public Health suggests even moderate consumption of red meat — as little as one serving a day — poses a more serious health risk than first thought.

Investigators followed more than 37,000 men from the Harvard Health Professionals Follow-Up Study and more than 83,000 women from the Harvard Nurses Health Study for up to nearly three decades. Participants filled in detailed questionnaires about their diet and lifestyle every four years.

A total of 23,926 deaths were found during the study period, including 5,910 from cardiovascular disease and 9,464 from cancer. The results were reported by Frank Hu, a professor of nutrition and epidemiology at Harvard, and his co-authors in this week’s issue of the Archives of Internal Medicine.

None of the participants had cardiovascular disease or cancer when the study began.

"This study provides clear evidence that regular consumption of red meat, especially processed meat, contributes substantially to premature death," Hu said in a release.

"On the other hand, choosing more healthful sources of protein in place of red meat can confer significant health benefits."

Eating more servings of processed meats like bacon carries a higher risk. (Molly Riley/Reuters)

Eating one serving a day of unprocessed red meat such as beef, pork or lamb that was 86 grams in size, about the size of a deck of cards, was associated with 1.13 times increased risk of mortality, the researchers said.

For processed meats like one hot dog or two slices of bacon, the risk rose to 1.20 times for every extra serving.

Healthier protein options

Red meat, especially processed meat, contains ingredients that have been linked to increased risk of cancer and heart disease, the researchers noted. Those ingredients include heme iron, saturated fat, sodium, nitrites and carcinogens that are formed during cooking.

On the other hand, the study's authors estimated that replacing a serving a day of red meat with other sources of protein, such as fish, poultry, nuts or lentils, lowered the risk.

Moderation is the key when it comes to eating red meat, said CBC medical specialist Dr. Karl Kabasele. He suggested balancing sources of protein over the week, including vegetarian meals.

The Heart and Stroke Foundation of Canada advises red meat eaters to:

• Opt for lean cuts.
• Watch serving sizes.
• Trim excess fat before cooking.
• Use low-fat cooking methods such as grilling, roasting, broiling and stir-frying.

Eating a diet rich in plant-based foods is protective, so substituting those foods for red meat offers a double benefit, Dr. Dean Ornish, an advocate for vegetarianism, said in a journal commentary accompanying the study.

In the study, men and women with higher intakes of red meat were less likely to be physically active and were more likely to smoke, drink alcohol and have a higher body mass. The researchers attempted to control for these variables, but it is difficult to separate out the effects of meat consumption from other lifestyle habits and a cause-and-effect relationship can't be determined.

Factors such as family history of heart attacks, cancer and Type 2 diabetes were taken into account in the analysis. Postmenopausal status and hormone replacement therapy were also included.

The study was funded by the U.S. National Heart, Lung, and Blood Institute and the U.S. National Cancer Institute.