Some foods leave an acidic effect on the body such as meat and dairy, while others leave an alkaline effect, like vegetables. However, are these effects significant enough to greatly alter the blood pH that seems to be strictly monitored by the kidneys, which keep it around 7.4?
Extracellular acid base homeostasis in human physiology is maintained primarily by the bicarbonate buffer, as regulated by both the kidneys and the lungs (and to a certain extent, the intracellular phosphate buffer). Outside of illness or injury, (arterial) blood pH is kept between 7.35 and 7.45. There is an excellent review of acid base homeostasis in Pubmed central that covers these points. Be aware before diving in, though, acid base homeostasis is one of the most complicated topics in human physiology.
As discussed in the reference above, a healthy pair of kidneys can usually compensate for a dietary acid or alkaline load. In these cases, what changes is not your blood, but your urine. There, is, though, some evidence that high blood pressure, diabetes, and possibly poor bone health may be associated with a chronic dietary acid load. Though an alkaline diet is being investigated as a treatment for chronic kidney disease, it is not currently approved for the prevention or treatment of any disease in the US.