How does the loss of bicarbonate due to diarrhea increase the protons in the blood?

Increase of protons (H+) in the blood causes acidosis. These effects decrease hemoglobin's affinity for oxygen and weakens its capacity to bind and increasing the haemoglobin dissociation.

Loss of bicarbonate stores by diarrhoea or tubular renal waste results in a state of metabolic acidosis leads increased concentration of plasma chloride and decreased concentration of plasma bicarbonate. Decrease in plasma bicarbonate leads to increase in H + ions causing acidosis.