Flashback Friday: How to Prevent and Treat Kidney Stones with Diet

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

This is what the surface of a kidney stone looks like under a microscope. Imagine that scraping down your urinary canal. Kidney stones affect approximately 1 in 11 people in the United States, though 20 years ago it was only 1 in 20, a dramatic increase in the prevalence of this disease, which started going up after World War II. Our first clue as to why was published in the 70s; a striking relationship was found between stone incidence and the consumption of animal protein. But this was a population study, though—you can’t prove cause and effect. So next, researchers in Britain did an interventional study, added animal protein to their diet, like an extra can of tuna fish to their daily diet, and measured stone-forming risk factors in their urine: how much calcium they were peeing out, the concentration of oxalate and uric acid in their urine before, and after, the extra tuna. Their overall probability of forming stones increased 250% during those days they were eating that extra fish. And that so-called high animal protein diet? That was just enough to bring intake up to that of the average American. So the average American intake of meat appears to markedly increase risk of kidney stones.

So what about no meat? Well even by the late 70s, we knew that the only dietary factor consistently associated with kidney stones was animal protein. And not just getting your first kidney stone. The higher the intake of animal protein, the more likely an individual is to have multiple stones, rather than just a single stone episode. Not protein in general, it seems, but specifically high in animal protein. Conversely, a diet low in animal protein may reduce the overall probability of forming stones to become very low indeed, which may explain the apparent low incidence of stones in vegetarian societies. So, it may be worthwhile advocating a more vegetarian form of diet as a means of reducing the risk.

But it wasn’t until 2014 when actual vegetarians were studied in detail. Using hospital admissions data, they found that vegetarians were indeed at a lower risk of being hospitalized for kidney stones compared to those who ate meat, and among meat-eaters, increasing meat intake is associated with a higher risk of developing kidney stones, whereas a high intake of fresh fruit, fiber, and magnesium may reduce the risk. We can use this information to advise the public about prevention of kidney stone formation.

What advice should we give in terms of which animal protein is the worst? Despite compelling evidence that excessive animal protein consumption enhances the risk of stone formation, the effect of different sources of animal protein had not been explored until this study was published in 2014. People who form kidney stones are commonly advised to restrict the intake of red meat to decrease stone risk, but what about chicken and fish? We didn’t know until now. Salmon and cod were compared to chicken breast meat, and burger and steak. They found that gram for gram, fish may actually be worse in terms of uric acid production. However, the overall effects were complex. Basically, stone formers should be counseled to limit the intake of all animal proteins, and not just a little bit. Only those who markedly decrease their animal protein intake may expect to benefit from dietary recommendations.

Studies suggest that excessive animal protein consumption poses a risk of kidney stone formation, likely due to the acid load provided by the high content of sulfur-containing amino acids in animal protein, as I explored in my video on preventing kidney stones with diet. But what about treating kidney stones? Most stones are calcium oxalate–formed like rock candy when the urine becomes supersaturated–so doctors just assumed if they’re made out of calcium, we just have to tell people to reduce their calcium intake. So that was like the dietary gospel for kidney stone sufferers until this study was published in the New England Journal of Medicine, pitting the two diets against one another—low calcium versus low animal protein and salt. And it was the restriction of animal protein and salt that provided greater protection: cutting the risk of having another kidney stone within five years in half.

What about cutting down on oxalates, which are concentrated in certain vegetables? A recent study found there was no increased risk of stone formation with higher vegetable intake. In fact, greater dietary intake of whole plant foods, fruits, and vegetables were each associated with a reduced risk independent of other known risk factors for kidney stones–meaning one may get additional benefits bulking up on plant foods, in addition to just restricting animal foods.

The reason a reduction in animal protein helps is not only because it reduces the production of acids within the body. A reduction in animal protein should also limit the excretion of urate–uric acid crystals that can act as a seed to form calcium stones, or can create entire stones themselves. Uric acid stones are the second most common kidney stones after calcium. There are two ways to reduce uric acid levels in the urine: a reduction in animal protein ingestion, or drugs. And removing all meat can remove 93% of uric acid crystallization risk. Here’s the risk of crystals forming eating the standard Western diet for five days. And then, switching to a vegetarian diet leads to a 93% drop in risk within days.

To minimize uric acid crystallization, the goal is to get the urine pH up to ideally as high as 6.8, so a number of alkalinizing chemicals have been developed. But we can naturally alkalize our urine up to the recommended 6.8 using purely dietary means; namely, by removing all meat, which takes someone eating the standard Western diet up from an acid 5.95 right up to the target of 6.8 eating a vegetarian diet. You can inexpensively test your own diet with a little bathroom chemistry, for not all plant foods are alkalinizing and not all animal foods are equally acidifying.

A so-called LAKE score was developed, a Load of Acid to Kidney score, which takes into account both the acid load of foods and their typical serving sizes, and can be used to help people modify their diet for the prevention of both uric acid and calcium kidney stones and other diseases. This is what they found. The single most acid-producing food was fish, like tuna. Then pork, then poultry, then cheese, though milk and other dairy only rate down here; then comes beef. Eggs are actually more acidic than beef, but people tend to eat less eggs at a sitting, so they come in here. Some grains can be a little acid-forming, such as bread, rice; but not pasta, interestingly. Beans are significantly alkaline-forming, but not as much as fruits, and vegetables, the most alkaline-forming of all foods.

Through dietary changes alone, we may be able to dissolve uric acid stones away completely–cure them. Now you see it, now you don’t. No drugs, no surgery, just telling them to drink more water and modify their diet, such as restricting the intake of animal protein, and the kidney stone was gone.

To summarize, here are the five types of kidney stones. And the most important things we can do diet-wise are to drink 10 to 12 cups of water a day, and reduce animal protein, reduce salt, eat more vegetables, and more vegetarian.

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Image credits: Kempf EK via Wikimedia Commons & Kidney Stoners. Images have been modified.