Intermittent Fasting (IF) has been creating quite a hype lately. It comes with a LOT of benefits (see this article), but it can also lead to some problems. The topic I want to discuss today is Can Intermittent Fasting Cause Kidney Stones?

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My Experience

I was practicing IF for about 7-8 months, sometimes fasting on a daily basis while other times only 3-4 times per week. One day I felt a strange pain on my left side, right where the ribs end. I assumed I made a wrong move or sat in a strange position and caused that. In less than half an hour the pain moved a bit lower and grew in intensity. Not long after that, the pain became almost unbearable. Turns out I had a kidney stone that left the right kidney…

I never had any kidney issues before, I had no idea I had kidney stones, so this came as a big surprise.

After some research, I found that intermittent fasting might be the reason I developed the stone, or at least it might have sped up the process.

Research Regarding a Possible Relation Between Intermittent Fasting and Kidney Stones

There are multiple research papers and studies published on this topic. Unfortunately, there is no consensus on this, and one can find totally different results. I think the best data source, in this case, comes from Muslims observing the Ramadan month. During this month, Muslims refrain from eating and drinking from dawn until dusk. The Islamic lunar calendar is 11 days shorter than the Gregorian calendar, and for this reason, the Ramadan month can occur during any season. This has a big influence on both the temperatures people are exposed to, but also on the duration of the fasting period (this can be between 12 and 18 hours).

I’ve found research papers indicating a significant variation in renal colic incidence during Ramadan fasting, but also papers indicating moderate or even no changes. For example, a team of researchers in Israel analyzed the data from the largest medical center in southern Israel, serving a population of Jews and Muslims. They found “a significant and positive association between RC and Ramadan while controlling to ambient temperature. In view of these findings, different prevention strategies should be investigated.1)I. Sagy, V. Zeldetz, D. Halperin, M. Abu Tailakh, V. Novack – The effect of Ramadan fast on the incidence of renal colic emergency department visits

A different study, conducted by a team in Ankara, Turkey, analyzed the number of patients admitted to the Kecioren Training and Research Hospital. They had a small number of patients (176), but concluded that there was no significant increase in renal colics during Ramadan, comparing to pre-Ramadan month 2)Yunsur Cevik, Seref Kerem Corbacioglu, Gulsah Cikrikci, Veysel Oncul, Emine Emektar – The effects of Ramadan fasting on the number of renal colic visits to the emergency department. They did notice though a significant difference between the first and second half of the Ramadan month.

There are a few other studies, with conclusions on both sides, but overall I’d say there are not enough high-quality studies with convincing results on this subject. Unfortunately, all the studies I’ve found were related to Ramadan fasting. I’d love to see a good study focusing only on intermittent fasting (without fluid restrictions), eventually combined with different alimentations styles (keto for example), done over extended periods of time.

Main Factors Contributing to Kidney Stones Formation

Kidney stones are in fact hard deposits of minerals and salts that bind together and grow in your kidneys. There are a few types of kidney stones, depending on how they are formed. Most divide the types into four main categories.

  1. Calcium stones. These are the most common kidney stones and are usually made of calcium oxalate. Oxalate is a substance produced by your liver or absorbed from your diet. Some foods are very high in oxalate: beer, beans, chocolate, nuts, berries, spinach, coffee. A high concentration of oxalate in urine leads to the formation and growth of kidney stones. In the calcium sones category, we also have calcium phosphate stones. These tend to form when the urine is highly alkaline. Phosphate stones are usually associated with metabolic conditions (hyperparathyroidism or renal tubular acidosis) or certain medications (like Topamax, Trokendi XR, Qudexy XR).
  2. Struvite stones. Our bodies can’t produce struvite. It is produced by some bacteria that normally live in the soil. This type of stones usually appear after a urinary tract infection and can become very large very fast.
  3. Uric acid stones. When the pH levels of the urine are very low (abnormally acid urine), uric acid molecules can bind together and form crystals.  When the pH levels are very low, these crystals can grow fast, forming big stones. Some of the most important factors leading to the formation of uric acid stones are severe dehydration (chronic diarrhea or malabsorption), a high-protein diet, obesity, and diabetes.
  4. Cystine stones. These stones form only in people who have an inherited kidney disorder called cystinuria3)Anna Zisman, M.D. – CHAPTER 9: CYSTINURIA: An Introduction for Patients.

In summary, the main risk factors for developing kidney stones are:

  1. Family and personal history. If somebody in your family had kidney stones, you are more likely to develop some also. If you already had one, you are likely to develop more.
  2. Dehydration. Not drinking enough water on a daily basis increases your chances of forming kidney stones.
  3. Diet. A diet high in protein, salt, and sugar also increases the risk.
  4. Obesity. Obesity has been linked to an increased risk (most likely because they produce acid urine)
  5. Certain medical conditions. Repeated urinary tract infections, cystinuria, hyperparathyroidism, or renal tubular acidosis increase the risk of kidney stones
  6. Certain supplements and medications, like vitamin D, vitamin C, calcium-based antacids, some medication used to treat migraines, can increase the risk of forming kidney stones.

Can Intermittent Fasting Cause Kidney Stones?

During fasting, there are several important things going on in your body. Probably the most talked-about is a drop in insulin levels. Insulin levels impact Sodium retention mechanisms in the kidney. There are many studies on the way insulin impacts Sodium retention, but unfortunately, there is no clear evidence or at least a consensus on this topic 4)Swasti Tiwari, Shahla Riazi, Carolyn A. Ecelbarger – Insulin’s impact on renal sodium transport and blood pressure in health, obesity, and diabetes, Michael W. Brands – Role of Insulin-Mediated Antinatriuresis in Sodium Homeostasis and Hypertension, Michael W. Brandscorresponding, M. Marlina Manhiani – Sodium-retaining effect of insulin in diabetes. The bottom line is that insulin levels do seem to have an impact on Sodium levels. Because you don’t eat, you also don’t ingest salt during this timeframe, as you would during non-fasting intervals.

The kidneys have very important roles in the body. Besides filtering out the blood and removing toxins, they also help control the blood pressure at good values, the volume of blood, or the number of red cells in the blood. The kidneys help maintain electrolyte concentrations by filtering electrolytes and water from the blood and excreting any excess into the urine. When you produce an imbalance and top that with less water, you put the kidneys under a lot of pressure.

I noticed I was indeed drinking less water during fasting. I used to drink one cup of coffee in the morning, then matcha or a green tea, one or two other cups of herbal or fruit tea. Plain water was only coming into play towards the evening when I used to drink one to three glasses of water. I am now way more careful to drink plenty of water throughout the day and I also add lemon juice at least to one of the glasses.

People who do IF usually are also careful what food they consume and tend to eat more vegetables, fruits, and nuts/seeds. These are high in oxalates, and as mentioned above, a high concentration of oxalate in urine leads to the formation of kidney stones. I am certainly guilty of that too… I do love meat, I’m far from a vegetarian, but I am also eating vegetables and I love fruits.

Conclusion

To sum it all up, I was not able to find convincing studies concluding that fasting is a serious cause of kidney stones, but my own experience makes me sustain this point of view. It took less than a year, after I took on intermittent fasting, to go from never having any kind of kidney issues to a week of severe pain. The pain was so bad, I am determined to make all the changes I have to in order to avoid going through that again. I know that once you have such an event it is very likely to keep going through similar ones, but hope dies last… I also believe that stones can be avoided through proper diet and hydration. I will discuss more regarding the steps I took and the changes I made in another post.

 

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