POST-menopausal women may be able to cut the risk of brittle bone disease with potassium bicarbonate supplements, say American researchers. In a study published in the New England Journal of Medicine, they say ordinary protein diets can cause production of more acid than the body can excrete. In a lifetime the body tries to redress the balance by using up alkaline salts from the skeleton, resulting in bone loss. A study of 18 women found that potassium bicarbonate, an alkaline substance, can compensate for this loss.