Sir,- I am writing in response to B. Skinner's letter (BDJ 2003; 195: 231) concerning the accumulation of calculus in patients on the Atkins diet. The Atkins diet is low in carbohydrate and results in weight loss because in carbohydrate deficiency, the level of Kreb's cycle intermediates is too low to enable dietary intermediates to be completely oxidised to carbon dioxide and water. This results in the accumulation of the partially oxidised intermediate acetyl-CoA, which is converted to ketone bodies (acetoacetate, β- hydroxybutyrate and acetone) which are then excreted.

The first two of these are acidic and in order to maintain the pH of the body at about 7.4, the body's reserve of buffering capacity, i.e. phosphate in the skeleton, is likely to be drawn upon. It is therefore hardly surprising that the Atkins diet is associated with an increased excretion of urinary calcium.

Is it possible that this is associated with a concomitant increase in salivary calcium concentration? An alternative explanation for the calculus accumulation could arise from changes in oral flora associated with this diet. When on a low carbohydrate diet, oral bacterial will also be carbohydrate deficient. Bacteria which can metabolise amino acids from dietary proteins as an energy source will therefore be at a biological advantage. They will proliferate at the expense of organisms which metabolise carbohydrate which has acidic end products. One end product of amino acid metabolism is ammonia which causes an increase in pH. This too would favour deposition of calculus. Whilst the Atkins diet may well be less cariogenic than the average diet, in terms of general health, it should be discouraged strongly.