Detailed comparison suggests plant proteins are better for the heart
If you’re among the millions of Americans who are eating more chicken because you think it has less fat and is better for your heart than a good ol’ hot dog or burger, researchers are offering some new food for thought. In a study that could debunk years of conventional wisdom, they say that red meat and white meat might actually be equal, at least when it comes to their effects on blood cholesterol. The researchers said the findings suggest that factors other than saturated fat might better explain the long-touted link between red meat consumption and heart disease.
The study, which is one of the first detailed comparisons of the effects of different sources of dietary proteins on blood cholesterol, also found that plant proteins are healthier for cholesterol than both red and white meat. The researchers published their results in the American Journal of Clinical Nutrition.
“When we began this study, we expected red meat to have a more adverse effect on blood cholesterol levels than white meat, but we were surprised that this was not the case—their effects on cholesterol are identical when saturated fat levels are equivalent,” said study leader Ronald Krauss, M.D., senior scientist and director of Atherosclerosis Research at Children’s Hospital Oakland Research Institute (CHORI).
But wait before racing out to stockpile your freezer with sausage and steaks. Krauss, who is also a professor of medicine at the University of California-San Francisco, noted that the study has some caveats. The meats studied did not include grass-fed beef or processed types such as bacon or sausage; nor did it include fish. Also, the size of the study—113 participants—was quite small, and its 16-week duration relatively short. And that, said Lawrence Fine M.D., D.Ph., Chief of the Branch of Clinical Applications and Prevention at NHLBI, argues for caution. “While this small study contributes new knowledge on the impact of dietary proteins on blood cholesterol, it is important to follow current dietary guidelines, which have been well-studied,” he said.
Still, Krauss said, the new findings offer a reason to begin re-evaluating some of the research driving those guidelines. “Our results indicate that current advice to restrict red meat and not white meat should not be based only on their effects on blood cholesterol,” Krauss said. “Indeed, other effects of red meat consumption could contribute to heart disease, and these effects should be explored in more detail in an effort to improve health.”
Red meat consumption has decreased steadily over the years, owing to widely-publicized concerns about increased heart disease risks associated with it. Government dietary guidelines have underscored those concerns by encouraging lean cuts of beef, pork, and lamb when they do get consumed. Those recommendations, Krauss said, have been based largely on observational studies linking red meat to risk of heart disease, due to red meat’s purported negative effect on blood cholesterol. White meat such as chicken and turkey, meanwhile, has been promoted as a better alternative because of its presumed healthier effect. But there has been almost no comprehensive comparison of the effects of these meat proteins and non-meat proteins on blood cholesterol until now, Krauss said. Non-meat protein sources include vegetables, dairy, and legumes, such as beans.
In the study, Krauss and his colleagues evaluated changes in the participants’ blood cholesterol levels after eating diets containing high levels of proteins from either lean red meat, lean white meat, or non-meat sources. The researchers also tested whether the effects of the dietary protein sources were modified by including high saturated fat (14 percent) and low saturated fat (7 percent) in each of the diets.
The study participants were 113 healthy men and women between 21-65 years old. They consumed each of the three high-protein diets for four weeks in random order, and the researchers tested blood cholesterol levels after each dietary type.
The researchers found that consuming high levels of saturated fat was associated with an increase in blood cholesterol, regardless of meat type, and that both types of meat protein resulted in higher blood cholesterol than the non-meat diets.
“Compared with the non-meat diet, both red and white meat diets increased blood levels of low-density lipoprotein (LDL) cholesterol—the so-called ‘bad’ cholesterol—by 6 to 7 percent with both high and low saturated fat intake,” Krauss said. “That may not seem like much, but that cholesterol spike would be expected to increase heart disease risk by several percent, or even more for some people. That should not be overlooked.”
The results of the study suggest that there may be factors other than saturated fat content that influence the cardiovascular effects of meat, Krauss said. A better understanding of these factors might help improve dietary guidelines in the future, he added.
Researchers are beginning to identify some of these culprits. For example, a previous analysis from the same study showed that daily consumption of red meat tripled blood levels of trimethylamine-N-oxide (TMAO), a gut-generated chemical that is linked to an increased risk of heart disease. Other studies have shown that certain chemicals used in processed red meat, such as sodium, nitrates, and their byproducts, may also contribute to the impact of red meat on the heart. Researchers have also identified daily intake of heme iron, a form of iron that is abundant in red meat and is easily absorbed by the body, as a factor in increasing heart disease risk.
“This study is part of an ongoing effort to better understand dietary risk factors for heart disease in an effort to promote overall health,” said Charlotte Pratt, Ph.D., a nutrition researcher who is the NHLBI project officer for the study. Pratt cautioned, however, that because of the small study population and short duration, more studies will be needed to confirm the findings. Other limitations of the study, including a relatively high participant dropout rate, also raised concerns, she added.
For now, Pratt, like Fine, also recommends following well-established dietary guidelines. “These findings support current advice to choose lean meats and include more beans, vegetables, fruits, nuts, and whole grains in your diet,” she said, citing the DASH Eating Plan, which emphasizes healthy food choices, as a scientifically demonstrated way to fight high blood pressure and heart disease.
Fine added that people should also practice other heart-healthy lifestyle changes, including aiming for a healthy weight, managing stress, increasing physical activity, and quitting smoking. He also said they should talk to their doctors about what changes are best for optimizing their individual heart health.
This study is called the APPROACH trial (Animal and Plant Protein and Cardiovascular Health). It was supported by NHLBI and the NIH National Center for Advancing Translational Sciences.