By Michael Anchors, MD, PhD
For years I have been telling dieters to avoid “diet” sodas because the artificial sweetener in them is too sweet. Sweet flavor itself raises insulin, blocking weight loss. Dieters would be better off with the high fructose corn syrup in regular Coke than with the aspartame in Diet Coke, or so I thought.
Now I must modify that advice. Overconsumption of cola-type drinks increases the occurrence of kidney stones, and that fact is especially true of the type sweetened with high-fructose corn syrup. The intake of fructose increases the urinary excretion of calcium and oxalate. Ninety per cent of kidney stones are composed of calcium oxalate. Moreover cola-type sodas, diet or non, contain phosphoric acid. Phosphate contributes to starting stones. Fresca and Sprite don’t have phosphate, but they are still fraught with the fructose issue.
There is abundant evidence that cutting dairy products out of the diet does NOTHING to prevent kidney stones. Ditto the advice to reduce coffee and chocolate. Any doctor who gives that advice should be ashamed; the truth is published everywhere. Google it, you’ll see. The ultimate cause of kidney stones is nanobacteria (read chapter 13 of my book Medical Myths Doctors Believe available on Kindle. But if the chemicals needed to produce stones are not present in the urine, the bacteria alone cannot create stones.
Given those heuristics, you wouldn’t know what to expect regarding the effect of sodas on stones. But the studies are clear. Consumption of cola-type sodas increases the occurrence of stones by about 24%. That’s for one soda a day. I have seen fat patients who consume a six-pack a day! Kidney stone pain is so terrible and the damage so severe, it is not a risk you should run. So the best advice is to stop drinking so many sodas of any type. If you are unwilling to modify your behavior that much, then it’s best to go back to Diet Coke, even though it has bad effects as far as weight.