Fish, a food recommended by nutritionists for its importance within a healthy and balanced diet, has been valued above all for its content of unsaturated fatty acids — omega-3s — which lower cholesterol levels in the blood and protect the cardiovascular system. Researchers have now turned their attention to its high biological value proteins, which, according to an analysis by the Nanjing University School of Medicine in Nanjing, China, are capable of significantly reducing the risk of stroke.

The analysis, published in the American medical journal Neurology, was coordinated by Xinfeng Liu, who led a research team across seven studies examining the link between protein-based diets and the incidence of neurological disease. In total, data from nearly 300,000 people were reviewed over an average of 14 years: the findings showed that regular intake of 20 grams of protein per day reduces the likelihood of suffering a stroke by 20 per cent. And that adding a further 20 grams of protein reduces the risk by 26 per cent.

The same experts cautioned against taking the study's findings too literally, however, because many animal sources of protein contain high levels of saturated fats, which can actually increase the risk of stroke. In this regard, Liu noted that two of the studies examined were conducted in Japan and a third in Sweden, countries where people tend to eat more fish than red meat. According to the experts, therefore, the correlation between higher protein consumption and lower stroke risk should be attributed primarily to the consumption of the high-quality, lean proteins found in fish.

"I don't think this study is suggesting that people start eating hamburgers and red meat," said Dr Ralph Sacco of the Miller School of Medicine, University of Miami. "It's important to focus on the consumption of lean proteins and plant proteins."

Doctors do not know exactly how proteins manage to protect us from stroke. It appears that they prevent hardening of the arteries, high blood pressure and diabetes, all of which are risk factors for stroke.