April 8, 2011 -- Vegetarians have a reputation for being ''heart healthy.'' However, a new report says some vegetarians may be increasing their risk of heart problems from nutritional deficiencies in their diets.
Overall, meat eaters are still at higher risk of heart attacks and strokes compared to vegetarians, says researcher Duo Li, a professor of nutrition at Zhejiang University in Hangzhou, China.
But in his review of published articles from medical journals, he found that vegetarian diets are often lacking in some key nutrients. These include vitamin B12 and omega-3 fatty acids. The deficiencies were especially evident, he says, in vegans. Vegans don't eat meat, fish, or any kind of animal product, including eggs and milk.
The deficiencies in B12 and omega-3, in turn, are linked with higher blood levels of an amino acid called homocysteine. The deficiencies are also linked with decreased levels of HDL cholesterol, the so-called good cholesterol, he says. High homocysteine levels have been suggested as a risk factor for heart disease. Higher HDL levels are heart protective.
"This may be associated with an increased thrombotic [blood clot] and atherosclerotic [hardening of the arteries] risk," he tells WebMD.
However, other nutrition experts say many vegetarians are already aware of the need to pay close attention to intake of vitamin B12 and omega-3s. They say the increased risk to heart health that Li suggests is only a hypothesis.
The study is published in the Journal of Agricultural and Food Chemistry.
Li scanned the medical literature to study vegetarian diets and their effects.
On the plus side, he found benefits to vegetarian diets. They are typically rich in fiber, magnesium, folic acid, vitamins C and E, and antioxidants.
They are low in total fat and saturated fat, cholesterol, and sodium. But they are also often low in zinc, vitamins A, B12 and D, and omega-3 fatty acids.
His advice? "Vegans or vegetarians should try to healthfully increase their B12 intake by regularly eating seaweed [popular in China] or fortified cereals," he says.
For a boost in omega-3s, he suggests plant oils such as flaxseed.
Vegetarians and Heart Health: Perspective
Two nutrition experts who reviewed the study put the findings in perspective.
The link between the deficiencies in vitamin B12 and omega-3 fatty acids and a higher heart disease risk is only a hypothesis at this point, says Lona Sandon, RD, a spokewoman for the American Dietetic Association and assistant professor of clinical nutrition at the University of Texas Southwestern Medical Center, Dallas.
"The majority of research on vegetarianism supports it as a heart health-promoting lifestyle," she says. The author carefully chooses the word 'may' [to suggest risk linked with the deficiencies] as there is little evidence to support his hypothesis at this time."