Don't Super Size It: Lifestyle, Eating Habits, and Renal Lithiasis

What are the long-term effects of regular consumption of fast food?

Urologists and pediatricians are puzzling over an apparent substantial increase in renal lithiasis among children.¹ In 2007, a singlecenter study found a nearly 5-fold increase in the number of children presenting with kidney stones.² A number of physicians "weighed in" (a pun that will need to be excused later) and said that their clinical experience suggests a current epidemic of pediatric renal lithiasis. For example, at Children’s Hospital in Philadelphia, the number of children treated for stones since 2005 has increased from 10 a year to as many as 5 per week.¹ There is a suspicion—rendered plausible by physiological data—that the increased incidence of stones may reflect yet another untoward consequence of fast food with its increased salt and calorie content.

HIGH SALT INTAKE AND STONE FORMATION
Let’s look at the salt first. Sodium and calcium excretion mirror each other in the urine. Therefore, with high salt intake (prevalent in fast foods) and consequent volume expansion, urinary sodium (and urinary calcium) excretion increases. The opposite, decreased salt intake with consequent volume depletion, reduces the "coupled" excretion of urinary sodium and calcium.

That "up/down pattern" explains the benefits of thiazide diuretics on volume, and as a result, on calcium excretion in the urine. A decrease in plasma volume resulting from a thiazide diuretic is followed by a decrease in both urinary sodium and calcium excretion. This outcome is good for patients with excess calcium excretion (hypercalciuria) and recurrent lithiasis.

But the benefit in these patients in response to thiazides is lost if salt intake increases and overcomes the volume depletion (urinary sodium and urinary calcium values then rise). This physiological formula may be jeopardy for a generation of children weaned on the high salt and caloric intake of fast foods. Now it is time to add calories to the salt theory, specifically regarding kidney stones.

HIGH-CALORIE DIET, OBESITY, AND KIDNEY STONES
Another study ties calories to the risk of renal lithiasis and not just in children.3 A database that contained stone-forming patients’ history (adults this time), body mass index, and "chemistries" (both urine and serum) was created. It was designed to address the question, "Is obesity a risk factor for stones?"

Obesity and the risk of stone formation unfortunately seem to go hand in hand. Obesity was statistically associated with stone events, and obese patients in this study had increased amounts of sodium, calcium, and uric acid in their urine collections. Obesity was the only strong predictor (a hazard ratio of 2.57) of a repeated stone event after a first episode of lithiasis. Weight control was recommended as an important intervention for kidney stone formers.

THE REAL PRICE OF A FAST-FOOD DIET
Taking stock of what the next generations are going to pay for high caloric and salt intake during their childhood will become a study of multiple organs and many complications. We need to keep our kids and ourselves away from the convenient fast-food fix. It will be more than our hearts that thank us!