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Do Low-Carb Diets Increase Kidney Stone Risk? Let’s Ask The Low-Carb Experts

Posted Mar 17 2011 1:41pm

People have all sorts of ideas about low-carb diets based on what they’ve heard somewhere or just on what they think they know about them. It’s why concepts like “artery-clogging” saturated fats still pervade our culture despite all the scientific evidence to the contrary . It doesn’t help that these myths surrounding healthy carbohydrate-restricted diets are perpetuated on a daily basis by so many so-called health “experts” in both the medical and nutrition fields and the general public is none-the-wiser to contradict any of it since they are merely living their lives and trusting the sources of information they are paying attention to. It’s what makes the idea of creating a cultural shift in thinking in favor of low-carb living that much more difficult–but it won’t deter me or the many others who are out here fighting the good fight to educate, encourage and inspire others to give livin’ la vida low-carb a try for themselves.

I literally receive hundreds upon hundreds of e-mails daily from readers who are searching for answers to their questions about their low-carb lifestyle, help with weight loss, or managing some chronic disease they are dealing with. Although I’m not a doctor or nutritionist, I’m always happy to share from my own experiences to see if that information can be beneficial to the person who wrote to me. It’s my pleasure to hear from readers and to offer up assistance in any way that I can. However, from time to time I’ll receive an e-mail from a reader who has an interesting question that is beyond my scope of full understanding enough to share a detailed explanation of what’s possibly going on. It’s okay that I don’t know everything there is to know about nutrition and it’s relationship to being healthy. The good news is I have a TON of connections with people who do. And I decided to tap into that resource again this week to answer a question that came from my fellow health blogger Kelly The Kitchen Kop .

She said she was working on a blog post about low-carb diets and their relationship to kidney stones after becoming concerned when she read a column by Perfect Health Diet author Paul Jaminet entitled “Dangers of Zero-Carb Diets, IV: Kidney Stones” where he argues that people consuming a ketogenic low-carb diet (less than 50g daily) are 500 times more likely to develop kidney stones comprise of uric acid and 50 times more likely to have the more common calcium oxalate kidney stones occur. You’ll recall I just had Paul Jaminet on my podcast last week where we talked about his aversion to people being in a ketogenic state which is why he recommends consuming white rice and potatoes to keep carbohydrate levels lowered but non-ketogenic. It seems Paul is of the opinion that uric acid development is much higher in people who eat a low-carb diet which is one of the culprits in kidney stones and is also a leading contributor to the development of gout (I’ve addressed the gout issue previously in this post ).

Of course, he’s referring to people on a “zero-carb diet” in his post and notes that carbohydrate calories should be 20% of total energy consumption. For some low-carbers, they’re already there. But does that mean those of us who for whatever reason choose to consume a more ketogenic level of carbohydrates are putting ourselves at risk for getting kidney stones? I didn’t know the answer, so I decided to throw this one to my expert friends in the low-carb research and medical community for some assistance in answering it. For the record, I’ve never had a kidney stone in my life and I’ve been eating high-fat, moderate protein, ketogenic low-carb for over seven years and counting. Could this be an issue that is less about your nutrition and more about genetic predisposition? Let’s find out!

Dr. William Davis, MD , cardiologist and health blogger at the “Heart Scan Blog”

I believe we know several things with confidence:

1) High animal protein intake increases urinary calcium loss
2) High animal protein intake decrease urinary pH (more acidic)
3) High animal protein intake decrease urinary citrate levels
4) High animal protein intake increases urinary urate

On the other hand, reduced carbohydrates reduces urinary calcium. Weight loss exerts multiple beneficial effects that decrease likelihood of urinary stone formation.

To my knowledge, there have only been studies looking at serum and urinary measures (e.g., oxalate, calcium, pH, etc.) that may be associated with stone formation, but there has not been a prospective study in humans that applies a low-carbohydrate diet versus conventional diet and observes the occurrence of stones.

So the bulk of observations on urine composition on low-carb diets suggests increased potential for urinary stone formation.

That said, it is also important to know that, as you know, “low-carb” comes in many flavors and can vary with regards to green vegetable composition, oxalate content, acid-base effects, etc. There are other factors that can also influence the tendency towards stone formation, such as vitamin D status, urinary magnesium excretion, hydration status (very important), dietary potassium content, etc.

All in all, low-carb likely increases likelihood of stone formation in those susceptible to the effect. However, there are a number of strategies to consider to mitigate the risk, such as vigorous hydration, balancing protein intake with generous green vegetable intake, magnesium and potassium supplementation, vit B6 supplementation. I advise some patients to monitor urinary pH and try to trend towards maintaining an alkaline pH (i.e., greater than 7.0).

Urinary stone formation is a complex topic with vigorous debate on just how important dietary content really is.

Dr. William Yancy, MD , researcher at Duke University and Veterans Administration Medical Center

There is only one article with empirical evidence on this and it only looked at precursors to stone formation. The study was published in the January 2, 2002 issue of American Journal of Kidney Disease called “Effect of low-carbohydrate high-protein diets on acid-base balance, stone-forming propensity, and calcium metabolism.”

Dr. Barry Groves, PhD , “Second Opinions” blogger and author of Trick and Treat

Yes, is the short answer. We have known that eating refined carbs lead to kidney stones for over 30 years, and that reducing carb intake is beneficial. Read my short article about this called “Kidney Stones and Kidney Failure Information” for more information.

Jacqueline Eberstein, RN , “Controlled Carbohydrate Nutrition” owner who worked with Dr. Atkins for 30 years

Over the years working with Bob Atkins we saw people with kidney stones. Most people had a history of past stone formation. Once one has had a stone more can follow. The most common stone being calcium oxalate. I don’t believe that doing low carb itself causes stones although obesity and metabolic syndrome can be contributing factors. Drinking large quantities of phosphates in soda also can be problematic. Interesting to note that in the last 30 years the incidence of stone formation is increasing as is obesity and metabolic syndrome. In patients with a history of stones we supplemented with magnesium as many of us are too low in magnesium and this can contribute to stone formation.

One of the most important factors in preventing stone re-occurrence is adequate hydration. This is especially important in the early stages of carb restriction when there can be a strong diuretic effect. Also people on diuretics are more prone to stone formation. The biggest caution I can give is stay hydrated especially if you have a history of kidney stones yourself or a family history.

Dr. Richard Johnson, MD , renal disease specialist at the University of Colorado-Denver

There is increasing evidence that soft drink intake is associated with kidney stones, and it has been linked with fructose intake. We have unpublished data that fructose intake results in a fall in urinary citrate, which is an inhibitor of stones. Thus, the decrease in urinary citrate could predispose those who drink soft drinks to develop kidney stones.

Dr. Stephen Phinney , noted low-carb researcher and co-author of The New Atkins For A New You

I need to point out that the cause of kidney stones is about where astronomy was before Johannes Kepler, but because kidney stones hurt like hell and people experiencing that much pain really, really want something (or someone) to blame. That said, here are some points to ponder:

• Nephrolithiasis runs in families, but we do not know what (or how many) genes are involved.
• People with metabolic syndrome or type-2 diabetes are more likely to develop kidney stones, but again we are a bit short on understanding the connection.
• Most kidney stones are made of calcium combined with either phosphate or oxalate, and after that come stones formed from urate (aka uric acid).
• When humans go on a ketogenic diet, their blood levels of uric acid go up for a period of 4-8 weeks, after which they come back down (even if they strictly adhere to the same level of carb restriction).
• This early effect of carb restriction has led some clinicians (I’m purposely withholding the word ‘scientist’ here) to suggest that low carb diets cause uric acid stones. Mechanistically, however, the rise in serum uric acid occurs because LESS OF IT is getting excreted into the urine due to competition with ketones. And obviously, kidney stones form in the fluid that is EXCRETED, not from what’s in the blood.
• Because low carb diets deliver superior results in the face of insulin resistance, people with metabolic syndrome or Type 2 diabetes tend to gravitate to this dietary treatment, which means that ‘stone-formers’ are attracted to carbohydrate restriction. Thus doctors may see a trend of more people with kidney stones who are on low carb diets, despite there being no causal link. (Gary Taubes waxes eloquently about this failure of epidemiology in Good Calories Bad Calories).
• High protein diets tend to contain more purines, which are metabolized by humans to uric acid, which in turn increases uric acid excretion and thus stone formation risk. This, among many other reasons, is why we counsel people that low carb diets should not be high protein diets. Around the globe, aboriginal cultures from the Arctic to Africa learned to treasure dietary fat over lean protein.
• A significant contributor to kidney stone formation is dehydration. Here is something that might significantly benefit your readership. When you take away peoples’ soda/pop and fruit juice, they tend to drink less fluid. Add to that the diuretic effect of nutritional ketosis and some people following low carb diets may be prone to being short of fluids much of the time. This is one of many reasons why I’m like a broken record in urging people on low carb diets to add 2 cups of broth/bouillon to their daily intake — not just in the first few weeks of adaptation — but permanently (as long as they stay low carb). And yes, 4-6 glasses of water per day probably also helps.

Be sure to read “An update and practical guide to renal stone management” published in the July 2, 2010 issue of Nephron Clinical Practice for more on this subject.

Now that the low-carb experts have weighed in, what say YOU? Have you ever experienced kidney stones? Did you even think for a moment that it was your low-carb diet that contributed to the development of them or had you been dealing with this issue long before you started livin’ la vida low-carb? Share your experiences with us in the comments section below so we can benefit from your wisdom regarding kidney stones and low-carb diets.

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