The average American eats a lot of red meat, such as beef and meat from other mammals. Meat-eaters often note that red meat has a lot of protein, which helps repair muscles and build bones. But new research shows that if people want to live a long and healthy life, they should get their protein from plants.

Dr. Mingyang Song and Dr. Andrew Chan work at Massachusetts General Hospital and Harvard University. They and other researchers examined how proteins from animals and proteins from plants affect human health.

They examined information from two major, long-term studies. The studies gathered information about the diet, lifestyle and health of more than 130,000 people. Dr. Chan says the information showed how to live a longer and healthier life.

One important finding was that people who ate the highest amounts of animal-based protein, such as red meat, had a higher risk of dying earlier. They were especially at risk of dying earlier from heart-related problems.

One reason is that red meat has high levels of cholesterol, which has been linked to heart disease.

The researchers found that heart-related -- or cardiovascular -- problems were higher among people who ate meat and also smoked, drank heavily, were obese and did not exercise.

While getting protein is important, red meat is not the only -- or best -- source. Dr. Chan said researchers found that people who replaced animal protein with plant protein in their diet reduced their risk of early death.

The study appears in the medical journal JAMA Internal Medicine.