Women over 50 who follow a high-protein diet could have a higher risk for heart failure, especially if most of their protein comes from meat, researchers report.
Greatest risk from animal protein
The study couldn't prove cause-and-effect. However, postmenopausal women with the most protein in their diet had a 60 percent increased risk of heart failure, compared with women who ate little protein, the study found.
The findings were presented at the American Heart Association annual meeting in New Orleans.
Most of the risk appears to come from animal protein, said study author Dr Mohamad Firas Barbour. He's an internist at Brown University's Alpert Medical School and Memorial Hospital of Rhode Island in Pawtucket.
Women who got most of their protein from vegetable sources appeared to have a nearly 20 percent reduced risk of heart failure, Barbour said.
Read: Protein facts
"The higher total dietary protein intake, that will increase the risk of heart failure, but higher vegetable protein intake appeared to be protective against heart failure," Barbour said.
Beans, nuts, lentils and quinoa are some non-meat sources of protein.
Heart failure occurs when the heart can no longer pump enough blood to fill the body's needs, according to the US National Institutes of Health. More than 5 million people in the United States suffer from heart failure, and it is the most common reason older people are hospitalised.
For this study, Barbour and colleagues analysed the self-reported daily diets of nearly 104,000 women between 50 and 79 years old, from 1993 to 1998. All subjects are participants in the Women's Health Initiative, an ongoing federally funded diet survey aimed at reducing heart disease, breast and colon cancer, and osteoporosis.
The research team also analysed urine samples from the women to further assess how much protein they regularly ate, Barbour said. This created a "calibrated" assessment of their protein intake.
Read: Protein facts for vegetarians
More than 1,700 women developed heart failure through 2005. Their odds for the condition was statistically associated with the amount of protein they ate, Barbour and colleagues report.
The researchers found an increased risk of heart failure from high-protein diets even after controlling for age, race, and other heart health risk factors like high blood pressure, diabetes or coronary artery disease, Barbour said.
He couldn't explain why protein might increase risk of heart failure, but speculated that high intake could lead some people to gain a lot of extra weight.
More study needed
Barbour expects the same findings would occur in men, "but you cannot tell until we do another study".
One heart specialist who reviewed the findings said more study may be needed.
Even though the authors tried to compensate for it, studies that rely on people to report what they eat tend to be a bit shaky, explained Dr Ileana Pina, a cardiologist and professor with the Albert Einstein College of Medicine in New York City.
"Some bias may be inserted when you're filling [out the survey] because you think you're being a good girl, you're doing the vegetables," Pina said.
Read: Major study confirms health benefits of lean protein
On the other hand, the study included a lot of women participating in a well-respected trial, said Pina, an American Heart Association spokeswoman.
"This is a study that collected an incredible amount of data," Pina said, adding that the researchers tracked new cases of heart failure and reported statistically significant findings.
The American Heart Association recommends a meal plan that focuses on fruits, vegetables, whole grains, low-fat dairy products, nuts, poultry and fish. The guidelines suggest keeping red meat and sugary foods and beverages to a minimum, and eating fish at least twice a week.
Data and conclusions presented at medical meetings are usually considered preliminary until published in a peer-reviewed medical journal.
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