Summary: When you eat a lot of sugar your body secretes insulin. Insulin, aside from handling the sugar load, also forces more calcium to be excreted through your kidneys. This increases your risk of forming kidney stones as a good amount of kidney stones are calcium based.
Dear Curtis: I have a diet that I know probably isn’t the best. Actually, I probably eat too much sugar. Problem is, I was just diagnosed with kidney stones. I’m getting the pain under control but I’d like to know. Could my diet be causing the kidney stones (especially the high sugar part)?
Based on the research that has been done to this point I think it is safe to say that your high sugar intake is playing a definite role in the formation of your kidney stones and is certainly putting you at higher risk at developing Diabetes down the road.
But, I want to add one caveat: it’s important that you understand that there are different types of kidney stones. And, with each type of different kidney stone is a different cause. So, when I’m talking about sugar contributing to kidney stone formation understand that I’m painting with a very broad brush stroke.
How Sugar Promotes Kidney Stone Formation
There have been a couple of smaller studies that have looked at this.
In one small study they took 20 patients (1). There were ten kidney stone patients and 10 healthy subjects. Each received 250 grams of sucrose (simple sugar) once a day for a week. The point of the study was to look at the effects of sugar intake on the kidneys. Sure enough, after one week there was rise in the levels of a substance called NAG (N-acetyl-B-glucosaminidase) in both groups. NAG is a marker of kidney damage.
But why is sugar damaging and how does it contribute to stone formation?
At this point it’s believed that it’s related to insulin secretion (2). For example, when you eat something that contains a good amount of sugar your body secretes insulin to handle the sugar load. However, insulin is a hormone that has a LOT of other effects in your body. One of which is that it sends more calcium to be excreted in the urine.
Now, normally calcium is excreted via the kidneys. But that’s normal concentrations. When insulin is released the amount of calcium going out through your kidneys now becomes higher and more concentrated. A good amount of kidney stones are calcium crystals. So, now you have more calcium in your urine and a higher amount of crystals forming.
This is one of the reasons why doctors suggest increasing your water intake when you have kidney stones. You can ‘dilute’ and flush out more of the smaller crystals. Of course, in your case, addressing the root cause of the problem is the important thing. So yes, I would definitely recommend cutting out the processed sugar in your diet.
- Li MK et al: Does sucrose damage kidneys? Br J Urol 58(4):353-7, 1986
- Blacklock NJ et al: Sucrose and idiopathic renal stone. Nutr Health 5(1):9-17, 1987