US researchers studied the effects of replacing all dietary protein with soy protein on female monkeys that had had their ovaries removed. This was designed to represent the process of menopause, which in humans causes greater risk of heart disease.
They also tested whether simply adding supplements of soy isoflavones, an antioxidant component of the soybean, to the normal diet could benefit heart health.
At the end of the study, those eating the soyfood diet had a significantly lower risk of atherosclerosis than monkeys who consumed all of their protein from milk. Atherosclerosis is the narrowing and hardening of the arteries, which is accelerated by high cholesterol and other risk factors. The condition is related to increased chances of heart attack.
Monkeys given isoflavone supplements along with the milk-based diet seemed to gain no protection to arteries.
Previous studies have shown that people who eat significant amounts of soy are less likely to develop heart disease. The plant is also thought to reduce cholesterol and foods containing soy protein can be marketed in some countries with a heart health claim as it is thought to lower cholesterol.
The researchers divided the monkeys into three groups of 20. The first was fed a diet likely to lead to atherosclerosis with milk-based protein, the second received protein from soy protein isolate and the third was fed a diet similar to the first group but with added soy isoflavones.
"Coronary artery LDL degradation was reduced by 50 per cent with soy but not with isoflavones," write the researchers in December's issue of Arteriosclerosis, Thrombosis and Vascular Biology (23:2241).
They add that the reduced LDL cholesterol seen with soy were due to decreased arterial LDL delivery, which could partly explain the protective effects of soy on arteries.
Soyfood sales are soaring in Europe, according to a recent report, with consumption of soya-based drinks and desserts up by over 20 per cent in 2002, valued at €1.3 billion, suggest authors Prosoy.