Optimizing Metabolism

by Ingrid Kohlstadt MD, MPH

Skipping Stones:

Using Diet and Nutrients to Prevent Kidney Stones

Rationale

Kidney stones are on the rise. As many as 1 in 9 Americans experiences a kidney stone. Half of people who have had a kidney stone experience recurrence. Kidney stones do not need to affect so many people; a “Stone Age” is preventable. This column equips readers with several simple steps towards preventing kidney stones, and explains the reasons underlying the suggestions.

I chose the topic because this is the summer edition of Townsend Letter, and summer is the season stones are most likely to roll. Additionally, the journal’s focus on heavy metal exposure is related to kidney stones in several ways: Heavy metals can contribute to the formation of some types of stones. Chelation can lead to kidney stones, thereby underscoring the importance of maintaining hydration and controlling inflammation during detoxification. Also, kidney stones are associated with chronic kidney disease, a disease process that been shown to respond to chelation in some clinical settings.

Rethinking Hydration

Hydration is not as simple as drinking more water. Here are some pointers on staying hydrated to prevent kidney stones:

• Don’t drink water in excess

  . Zealous consumption of water to flush out a kidney stone can be harmful. Excessive intake of water interferes with electrolyte balance and has claimed lives, especially of people engaging in endurance athletics. Dehydration from athletics and sauna use are similar to dehydrations from medical conditions such as blood loss, diarrhea, vomiting, poor intake of fluids, and respiratory losses. Medical treatment of dehydration is a combination of water, electrolytes, and sugar. Examples are chicken broth, coconut water, Pedialyte, oral rehydration salts, and intravenous fluids. A small amount of protein added to the hydrating fluid may be additionally beneficial.

• Don’t drink calories

  . Sports drinks add too much sugar. Most are a 6% sugar solution instead of the 2% solution optimal for absorbing water from the intestinal tract and recommended by the World Health Organization for rehydration. Sugar added to water promotes weight gain, more than if the sugar were eaten. Calories consumed in beverages are not as satiating as calories from food.

• Use fluid to replace all electrolytes, not just sodium.

  Sodium makes the two common forms of kidney stones worse. It is frequently overlooked that some bottled waters contain significant amounts of sodium.

• Add citrate to your water.

  Lemon and lime juice are an excellent source of citrate and they alkalinize urine. At first glance it may appear contradictory that citrus, which has acidic pH, can alkalinize the urine. Citrate helps form bicarbonate through the Krebs cycle, also called the citric acid cycle. So even though the physical chemistry is acidic, the net biochemical effect on the metabolism is alkalinizing.

• Avoid added fructose, which frequently hides in fruit drinks and sodas.

  Increased dietary fructose may increase stone risk by as much as 38%. In magnesium deficient animals and humans, increased fructose intake increases urinary calcium excretion. Fructose increases uric acid levels.

• Avoid artificially sweetened beverages.

  Most high-intensity (artificial) sweeteners create an osmotic load, which contributes to dehydration. Most lower urine pH.

• Choose fruit tea, green tea, and coffee.

  Not only do these beverages avoid the pitfalls in hydration described above, preliminary studies suggest that unique phytonutrients found in cranberry juice and green tea may exert yet uncharacterized antilithogenic properties for some stone types.

• Breathe in hydration.

  Staying well-hydrated isn’t limited to beverages. Eating hydrous foods and humidifying a room may be helpful.

• Be mindful of hydration when traveling to higher elevation.

  Higher elevation prompts more rapid breathing and increases respiratory fluid losses, especially in dry climates.

• Be aware that excess body fat is a set-up for chronic underhydration. Excess fat weight is a reason to be extra vigilant about hydration.

  The more excess body fat someone carries, the more likely s/he is to be dry and hot. The underlying cause is simply that oil and water don’t mix. Muscle contains much more water than fat does. For example, someone with extreme obesity may only have 35% total body water compared with the recommended 65%, regardless of how much water that the person drinks. Fat also decreases the ratio of body surface area to volume, additionally complicating heat exchange and metabolic rate.

Eat Right for Your Stone Type

For all stone types, acute management involves hydration and evaluation for associated conditions such as obesity, insulin resistance, kidney structural changes, urinary tract infection, chronic kidney disease, and hyperparathyroidism. But other recommendations are stone specific, as illustrated with the following analogy:

I never had a throwing arm. My childhood attempts to skip stones along the Chesapeake Bay resulted in one sound, thunk. Years later, while studying rural medicine in Alaska, I visited Katmai National Park. There I found a new paradigm. The porous, smooth pumice from Mount Katmai’s 1912 eruption flitted across the water like dragonflies on a Japanese silk tapestry, and I could skip them a dozen times each. The solution was found in the type of stone.

New research shows that several changes in diet and nutrients, when taken together can help adults skip (as in, not have) kidney stones. The solution is found in the type of stone one is trying to prevent. The following are suggestions on how to eat and drink right for your stone type:

Calcium Oxalate Stones

This is the most common stone type, accounting for approximately 62% of kidney stones.

• Since these stones form when the urine is acidic, adding a daily dietary source of an alkalinizing food or beverage is important.

• Potassium citrate supplementation has been shown effective at reducing stone risk.

• If urine calcium is high, restricting sodium to no more than 2 grams a day is important.

• With low urine magnesium, increasing dietary magnesium and supplementing with magnesium citrate are beneficial.

• Excess protein (more than 30% of dietary intake) should be avoided.

• Supplemental vitamin D in excess can increase uptake and urinary excretion of calcium, but some consider inadequate vitamin D a risk factor as well.

• When urine oxalate is high, there may be modest benefit, if any, in restricting intake of oxalate-rich foods such as nuts and spinach. An interesting hypothesis now gaining substantiation is that improving gastrointestinal health may reduce urine oxalate levels. Dietary oxalate is broken down by bacteria in the intestinal tract called O. formigenes. Colonies besieged by infection, overgrowth, or antibiotics do not break down as much oxalate. Then no matter how much oxalate the diet contained, more oxalate is absorbed. Subsequently, the oxalate is excreted in the urine, increasing the risk of calcium oxalate stones. Antibiotics increase risk of stone recurrence, possibly by altering gut flora.

Uric Acid Stones

Uric acid stones account for approximately 17% of kidney stones. Alkalinizing the urine, decreasing protein intake, avoiding beer and alcohol, and reducing fructose intake are all opportunities for prevention.

Calcium Phosphate Stones

Calcium phosphate stones account for approximately 16% of kidney stones in adults and double that rate in children. Urine does not need to be alkalinized. In fact acidifying measures can be taken. These include drinking cranberry juice (cranberries are one of few acidifying fruits), replacing sodium losses from athletics and sauna use, and supplementing with betaine hydrochloride. Reducing calcium excretion may be additionally beneficial.

Struvite Stones

Struvite stones are uncommon, accounting for approximately 3% of all kidney stones. They are often associated with infection. Therefore hydration and phytonutrients shown to reduce bladder infections are likely to be beneficial. Urine does not need to be alkalinized. Supplemental magnesium should be avoided.

Even if you don’t know your type, you can take preventive steps.

• A family history or associated condition can guide your suspected stone type.

• Urine characteristics can be measured even when no stone has been retrieved.

• Alkalinizing urine will be preventive most of the time, since more than half of kidney stones among adults are calcium oxalate and roughly another quarter are uric acid stones.

• Maintaining healthful gastrointestinal flora has benefits which extend beyond calcium oxalate stone prevention.

• Maintaining optimal weight through diet and exercise reduces risk of all stone types.

• The earliest sign of chronic kidney disease should be treated aggressively with diet, regardless of stone type.

Conclusion

Emerging science suggests we rethink the truism “The most simple and important dietary change to prevent stones is to drink plenty of fluids.” Hydration is not simple. A closer look at the nuances of hydration can augment prevention. The beverages and food one chooses also influence stone risk. Some of these recommendations are specific to the type of stone.

Those interested in details on drug interactions and clinical practice-oriented tables may be interested in my coauthored review in American Family Physician, forthcoming later this year.

Ingrid Kohlstadt MD, MPH, has been elected a Fellow of the American College of Nutrition and the American College of Preventive Medicine, and is an associate at the Johns Hopkins Bloomberg School of Public Health. She recently completed a two-year appointment at the FDA working in the Office of the Commissioner, and published one of Medscape Public Health’s “Top Ten CMEs for 2010.” Dr. Kohlstadt is the founder and chief medical officer of INGRIDients Inc., editing Food and Nutrients in Disease Management (CRC Press; Jan 2009) and Scientific Evidence for Musculoskeletal, Bariatric and Sports Nutrition (CRC Press; 2006).