Delay of stroke onset by milk proteins in stroke-prone spontaneously hypertensive rats.

BACKGROUND AND PURPOSE There is an inverse association between dairy food consumption and the incidence of stroke in observational studies. However, it is unknown whether the relationship is causal or, if so, what components in milk are responsible for reducing the incidence of stroke. METHODS Stroke-prone spontaneously hypertensive rats were fed diets comprising amino acids, proteins from different sources (casein, whey, soybean, or egg white), or fats from different sources (butter, beef tallow, or cocoa butter) and the onset of stroke and lifespan were examined. RESULTS Increasing the amount of dietary casein (5% to 55% of caloric intake) markedly delayed the onset of stroke. However, when stroke-prone spontaneously hypertensive rats were fed diets containing 55% of caloric intake as protein, rats fed casein or whey protein, a major component of milk, displayed a delayed onset of stroke compared with rats fed soybean or egg white protein. Rats fed an amino acids diet containing the same amino acids composition as casein did not have a delay in the onset of stroke. Increasing dietary fats, including butter as well as beef tallow and cocoa butter, did not affect the onset of stroke. All diets did not affect blood pressure in the early stage. CONCLUSIONS These data suggest that the inverse association between dairy food consumption and incidence of stroke in epidemiological studies is causal and that peptides in milk protein, but not fat, might be responsible for this effect.