Do not cut calcium out of your diet to prevent kidney stones
People with calcium-oxalate stones are often told to eat less calcium, but a trial found the opposite dietary approach worked better. Men with recurrent stones who ate normal amounts of calcium while reducing animal protein and salt had about half as many recurrences over five years as those on a low-calcium diet. UK guidance also advises against restricting dietary calcium.
What it takes
Nothing. It also saves the effort of constantly avoiding calcium-containing foods.
What you may gain
A five-year randomized controlled trial enrolled 120 men with recurrent calcium-oxalate stones and idiopathic hypercalciuria, meaning high urinary calcium without an identified secondary cause. One group consumed normal calcium, 30 mmol/day, with reduced animal protein, 52 g/day, and sodium chloride, 50 mmol/day. The other followed a traditional low-calcium diet of 10 mmol/day. Recurrences occurred in 12/60 versus 23/60 participants: unadjusted RR 0.49 (95% CI 0.24–0.98; P=0.04), about half the risk. Urinary calcium fell by about 170 mg/day in both groups. Urinary oxalate rose by 5.4 mg/day in the low-calcium group but fell by 7.2 mg/day in the normal-calcium group. NICE NG118, recommendation 1.8.1, advises maintaining rather than restricting dietary calcium: 700–1,200 mg/day for adults and 350–1,000 mg/day for children and young people depending on age. “The stones contain calcium, so eat less calcium” is intuitive but does not capture the whole process.
Context & considerations
The trial included only men with recurrent calcium-oxalate stones and high urinary calcium, so it cannot be applied automatically to every stone type. It also changed three things together—calcium, animal protein, and salt—so the full benefit cannot be assigned to calcium alone. The point is to avoid unnecessarily eliminating calcium-containing foods, not to add calcium supplements. Dietary calcium and supplements are different questions; people with a stone history should ask their treating clinician about supplements. For fluid intake, see drinking 2.5–3 liters daily after kidney stones.
Research & references
Borghi L, Schianchi T, Meschi T, et al. (2002). Comparison of two diets for the prevention of recurrent stones in idiopathic hypercalciuria. New England Journal of Medicine, 346(2), 77–84. https://doi.org/10.1056/NEJMoa010369; National Institute for Health and Care Excellence (2019). Renal and ureteric stones: assessment and management. NICE NG118, recommendation 1.8.1. https://www.nice.org.uk/guidance/ng118/chapter/Recommendations.