Overall, the participants with the highest amount of protein in their diets were 20 percent less likely to develop a stroke than those with the lowest amount of protein in their diets. The results accounted for other factors that could affect the risk of stroke, such as smoking and high cholesterol. For every additional 20 grams per day of protein that people ate, their risk of stroke decreased by 26 percent.
"If everyone's protein intake were at this level, that would translate to more than 1.4 million fewer deaths from stroke each year worldwide, plus a decreased level of disability from stroke," said Liu.
Liu noted that the analysis does not support increased consumption of red meat, which has been associated with increased stroke risk. Two of the studies were conducted in Japan, where people eat less red meat than westerners do and more fish, which has been associated with decreased risk of stroke.
"These results indicate that stroke risk may be reduced by replacing red meat with other protein sources, such as fish," Liu said.
The reduced risk of stroke was stronger for animal protein than vegetable protein.
Protein has the effect of lowering blood pressure, which may play a role in reducing stroke risk, Liu said.