How to reduce risk of kidney stones after bariatric surgery

The Centers for Disease Control and Prevention (CDC) reports that 22.1 percent of adults in Washington, D.C., are obese. Though that’s lower than the national obesity rate of 36.5 percent, it still means more than one in five adults in our area has a serious weight problem.  

Many people who can’t lose enough weight through diet and exercise turn to weight loss surgery, or bariatric surgery. Bariatric surgery is a great option to help people lose weight. But we’ve noticed that patients who have bariatric surgery have a greater risk for kidney stones than people who haven’t had this procedure.  

Kidney stones are a significant medical problem, and they can increase your chance of developing serious issues like kidney damage and recurrent infections. We can work to identify and lower your risk for having kidney stones after your weight loss surgery.  

The relationship between bariatric surgery and kidney stones

In one study, researchers looked at a group of obese patients who had bariatric surgery and compared them to a group of obese patients who didn’t have surgery. These two groups had similar rates of developing kidney stones at the start of the study.  

But afterward, 11 percent of the patients who had surgery developed new kidney stones within six years of their surgery, compared to 4.3 percent of the patients who didn’t have surgery. Put another way, the patients who had bariatric surgery were over 255 percent more likely to develop new kidney stones than the patients who didn’t have surgery.  

This happens because bariatric surgery causes changes to patients’ urine that make kidney stones more likely. The kidneys filter waste products from the bloodstream that are absorbed in the food we eat. Some of the urinary changes we commonly see after bariatric surgery include:

  • Decreased amounts of urine, which is caused by dehydration and can concentrate waste products to form kidney stones more easily
  • Increased levels of a compound called oxalates
  • Increased levels of calcium, which enters the bloodstream when a diet is too high in salt, or sodium  

#BariatricSurgery causes changes to patients’ urine that make #kidneystones more likely. via @MedStarWHC

Having high levels of calcium and oxalates in concentrated urine increases the risk of developing calcium oxalate kidney stones, which are the most common type of kidney stone.

Reduce your risk of kidney stones after weight loss surgery

Reducing the risk of kidney stones is important for everyone, but it’s especially important for patients who have had bariatric surgery. Drinking enough water, decreasing salt intake and eating less animal protein are a few things everyone can do to lower their risk.

Related reading: Kidney stone diagnosis and treatment

But there are specific steps I recommend that patients who have had bariatric surgery take to reduce their risk. These steps relate to the levels of oxalates and calcium in a patient’s urine.

Oxalates

People who have had bariatric surgery need to reduce the levels of oxalates in their diets to avoid kidney stones. Oxalates are found in a wide variety of fruits, vegetables and grains. Oxalate levels in food can vary depending on many factors, including where they’re grown and when they’re harvested.

People who have had #bariatricsurgery need to reduce the levels of oxalates in their diets to avoid #kidneystones. via @MedStarWHC

Your doctor can help you determine which foods to avoid. But in general, the following foods tend to be high in oxalates:

  • Spinach
  • Tea
  • Cola
  • Soy
  • Nuts

I also recommend that you talk to your doctor if you take a vitamin C supplement. One study showed that men who took a 1,000-milligram vitamin C supplement on a regular basis had double the risk of calcium oxalate kidney stones over men who didn’t take a supplement. This may be because the body disposes of excess vitamin C in the form of oxalates, which end up in urine.  

Calcium

Oxalate levels in the urine aren’t just tied to oxalate-rich foods. Calcium levels also play a role in the amount of oxalates that end up in urine. A lack of calcium in your diet can increase the amount of oxalates that make their way to the kidneys.

All of our bariatric surgery patients are instructed to take calcium supplements following their procedures. We recommend that patients take at least 1,500 milligrams of calcium per day. Taking calcium citrate supplements as opposed to calcium carbonate may help, as people with low levels of citrate are at increased risk for kidney stones. Citrate is a compound found in citrus fruits like lemons and oranges.  

Getting the calcium you need in your diet is the best option. Foods that are rich in calcium include:

  • Watercress, kale and arugula
  • Green beans 
  • Low-fat cheeses, milk and other dairy products

Reducing salt is important for maintaining healthy calcium levels. Salt, or sodium, causes the body to lose more calcium than normal. That calcium ends up in urine. Most people get far too much salt in their diets in the form of processed foods, so watch for sodium levels on nutrition information when you shop for groceries.  

What to watch out for after bariatric surgery

It’s a good idea to ask your bariatric surgeon about the risk of kidney stones. We work closely with our bariatric surgeons to minimize patients’ risk after surgery.

Make sure to watch for the signs of kidney stones if you’ve had bariatric surgery. These symptoms include:

  • Blood in your urine
  • Loss of appetite
  • Nausea or vomiting
  • Sudden, severe pain in the side or mid-back  

You may also notice a fever or chills along with any of these symptoms. This can be a sign of an infection. Request an appointment with one of our urologists if you notice any of these symptoms.  

Bariatric surgery can be life-changing—not to mention lifesaving—for many patients who struggle with obesity. But it can increase your risk of kidney stones. Making smart decisions about your diet after surgery can help you reduce this risk so you can focus on living a healthier life. 

Daniel Marchalik, MD, is Director of Ambulatory Urologic Surgery and Director of Medical Education at MedStar Washington Hospital Center. He is also an instructor at MedStar Georgetown University Hospital. As a urology specialist, he uses noninvasive, minimally invasive, and endoscopic methods to treat some of the most common conditions in urology, such as stone disease, voiding difficulty caused by prostate enlargement, and elevated PSA.

Dr. Marchalik places a strong emphasis on preventative care such as medical and dietary modifications for the prevention of kidney stones. His clinical interests include medical and surgical treatment of stone disease as well as the use of advanced imaging techniques specifically, the innovative use of ultrasound and MRI fusion to analyze the health of the urinary tract. Dr. Marchalik’s focus on and experience with MRI-fusion biopsy of the prostate can provide patients with important and necessary information that may help guide their treatment.

View Profile