High protein diet increases risk of kidney stones

Consumption of low-carbohydrate high-protein (LCHP) diets for 6 weeks leads to a marked acid load to the kidney, increases the risk for stone formation, decreases estimated calcium balance, and may increase the risk for bone loss. Diets heavy on foods that are high in protein and low in carbohydrates can increase the risk of kidney stones and reduce the body's ability to absorb calcium after just six weeks. LCHP diets are commonly used for weight reduction. The researchers from the National Kidney Foundation, University of Chicago, explored the relationship between such diets and acid-base balance, kidney-stone risk, and calcium and bone metabolism. Ten healthy subjects, aged 21 to 52 years, participated in the study. Subjects initially consumed their usual non-weight-reducing diet, then a severely carbohydrate-restricted induction diet for 2 weeks, followed by a moderately carbohydrate-restricted maintenance diet for 4 weeks. It was found that six weeks on a low carbohydrate, high protein diet increased the acid load to the kidneys, raising the risk of kidney stones. Animal protein has been shown to boost urinary excretion of oxalate, a compound that combines with calcium and other compounds to form kidney stones. The participants lost an average of 4 kg, but most developed ketones-compounds formed when the body uses its own fat as fuel and that can raise acid levels in the blood. Acid excretion, a marker of acid levels in the blood, rose by 90% in some participants, but none of them developed metabolic acidosis. Urinary calcium levels also rose sharply. Although low carbohydrate, high protein diets result in weight loss in the short term, they are less successful in the long term and may even be hazardous to health, researchers have warned. Protein rich foods can be high in fat, which increases the risk of heart disease and type 2 diabetes. Diets heavy in foods with low levels of carbohydrate, such as fruit and vegetables, can also leave the body hungry for essential vitamins and minerals, and insufficient glucose from carbohydrate that can lead to fatigue and dizziness. Although it is not clear from the study whether bone mass was affected, the findings show that such diets may increase the risk of bone loss over the long term.