You’ve probably seen the claims online. “Fasting protects your kidneys.” “Skip breakfast and watch your GFR go up.” Maybe a friend lost weight doing 16:8. Or someone in a Facebook group swears fasting changed their labs.
So now you’re wondering if you should try it. Could fasting help my kidneys, or could it make things worse? That’s a fair question. With chronic kidney disease, every food choice can already feel like a test.
As a renal dietitian, I don’t recommend fasting for people with CKD. The research is still too early, and the risks are real. The one exception is fasting for religious reasons. In that case, close monitoring with your nephrologist and kidney dietitian is a must. My goal is always to help you enjoy as much food as possible while protecting your kidneys. Fasting does the opposite, adding more rules and less room on your plate.
If fasting has worked for you or someone you know, I’m not here to dismiss that experience. Your experience is real, and it matters. But one person’s experience isn’t evidence. It’s an anecdote, and there’s no way to know if it would work the same way for someone else.
That’s why this article focuses on the research, which looks at many people at once. That bigger picture shows us what’s most likely to help or harm people with kidney disease. In this article, I’ll walk you through what the research actually says and why I still don’t recommend fasting. Then I’ll share what works better for your kidneys.
Table of Contents
Types of Fasting and What the Research Says
What Is Fasting?
Fasting means going without food, and sometimes drinks, for set periods of time. There are several types, and they don’t all affect your kidneys the same way.
2 Questions That Matter Most for Your Kidneys
The biggest differences between fasting types come down to 2 questions:
- Can you still drink water?
- Are you still getting enough nutrition?
Keep those in mind as you read about each type below.
How Much Research Is There on Fasting and Kidney Disease?
Research on fasting and kidney disease is still small (1). Much of it was done in animals, so these results are promising, not proven.
Time-Restricted Eating (16:8)
What Is Time-Restricted Eating?
You eat during a set window each day. The most popular version is 16:8, where you eat within 8 hours (like 10 AM to 6 PM) and fast for the other 16.
You can still drink water during fasting hours. That makes it less risky than fasts without water, but less risky isn’t the same as recommended.
Can Time-Restricted Eating Help Kidney Function?
In one small study, people with stage 3 and 4 CKD who were also at a higher weight tried 16:8 eating for 12 weeks (2). Their doctors watched them closely the whole time.
Compared to people who didn’t fast, the 16:8 group:
- Saw a small rise in eGFR (about 3 points)
- Lost weight
- Had lower uric acid
- Had healthier changes in their gut bacteria
No one in the study had serious side effects.
What These Results Do and Don’t Tell Us
The study excluded several groups of people, including those following a vegetarian diet, those with type 2 diabetes taking insulin, and those with severe hypertension.
And this was a very small study, with only 13 participants taking part in the time-restricted feeding group.
Furthermore, the researchers acknowledged that because the groups were non-randomized, results between the two groups could have been impacted by bias.
A 3-point change in eGFR is pretty small. This kind of change in GFR could also happen simply from a change in hydration status.
It’s interesting research, but it’s one small study. That’s not enough to recommend 16:8 as a way to protect your kidneys.
Early vs. Late Eating Windows
Some studies have compared eating windows earlier in the day with ones later in the day.
In a review of 12 studies in adults with extra weight (but do not have chronic kidney disease), both led to about the same weight loss (3).
But the earlier eating windows did better for insulin resistance, blood sugar, and blood pressure (3).
Another study found the same pattern, with bigger drops in fasting blood sugar and the bottom number of blood pressure when people ate earlier (4).
Why Meal Timing May Matter for Your Kidneys
Your kidneys follow a daily rhythm, just like your sleep. How well they filter and how much protein shows up in your urine both change throughout the day (5).
A large US survey found that people who did most of their eating later in the day had higher odds of diabetic kidney disease (6). Those who ate earlier had less protein in their urine.
How many hours people ate didn’t seem to matter, but when they ate did. That study only shows a link, not cause and effect, but it suggests timing may matter more than fasting.
Intermittent Fasting (Full-Day Fasts)
What Is Intermittent Fasting?
You switch between eating days and fasting days. For example, you might fast for a full day once or twice a week, or every other day.
Is Intermittent Fasting Safe With Kidney Disease?
There’s very little research on full-day fasting in people with CKD. It also tends to be harder to stick with than 16:8.
Going a full day without food can make it harder to get enough protein and calories. You’ll see why that matters in the risks section below.
Fasting-Mimicking Diet (FMD)
What Is a Fasting-Mimicking Diet?
A fasting-mimicking diet is a planned, very low-calorie way of eating for about 5 days each month. You still eat small amounts of food, but your body responds in some ways like it’s fasting.
Can a Fasting-Mimicking Diet Lower Protein in the Urine?
In a small pilot study, people with CKD followed a fasting-mimicking diet 5 days a month for 3 months. They had less protein in their urine and better blood vessel health (7).
Protein in the urine (called proteinuria) is a sign your kidneys are under stress. So less protein leaking out is a good thing.
Planned Programs vs. Eating Very Little on Your Own
These studies used specific, planned meal programs with medical support. That’s not the same as eating very little on your own for 5 days.
Ramadan and Other Sunrise-to-Sunset Fasts
What Is Sunrise-to-Sunset Fasting?
This type of fasting means no food or water from sunrise to sunset, often for a full month. It’s the most studied type of fasting in kidney disease.
This means fasting can last anywhere from less than 6 hours to over 18 hours.
Is Ramadan Fasting Safe With Kidney Disease?
In people with stage 2 to 4 CKD, eGFR didn’t change much during Ramadan. Hydration dipped for a while, then returned to normal about 4 weeks later (8).
In people with stage 3 CKD and diabetes, there were no differences in weight, blood pressure, or labs (9). Those who fasted and those who didn’t looked about the same.
How Your CKD Stage Changes the Risk
Risk of acute kidney injury (AKI) or further kidney damage goes up as kidney function goes down. Experts generally rate it this way (10):
- Stages 1 and 2: lower risk
- Stage 3: moderate risk
- Stages 4 and 5: high risk
Some studies also found early signs of kidney stress, even when eGFR looked stable (10). That’s because going without water for many hours is hard on the kidneys.
Expert Guidance for Fasting During Ramadan
A team of kidney experts created a plan to help people fast more safely during Ramadan (10). For people at moderate risk, they recommend a doctor check-in and labs before, during, and after the fast.
For people at high risk, they encourage exploring other options. Your healthcare team (and your faith leader, if helpful) can talk those through with you.
Finally, note that most fasting is researched to determine safety, not if it provides benefits to people with CKD.
Long-Term Calorie Cutting
What Is Long-Term Calorie Cutting?
This means eating much less than your body needs, every day, for months at a time.
Can Cutting Calories Help Your Kidneys?
In rat studies, big calorie cuts led to better kidney labs (11). But in people with CKD, experts worry the same approach can cause muscle loss, weaker bones, and slower healing (12).
That’s why this is the type to be most cautious about. When it comes to cutting calories, more isn’t always better.
In fact, the National Kidney Foundation and the Academy of Nutrition and Dietetics advise a normal to higher calorie intake for people with CKD. (13)
Fasting and Polycystic Kidney Disease (PKD)
Can Fasting Slow Cyst Growth?
You may have seen buzz about fasting for PKD. In animal studies, fasting slowed cyst growth (14).
What the Latest PKD Guidelines Say
The newest international PKD guidelines (KDIGO 2025) found no proof yet that fasting helps kidney function in people with PKD (15). Studies are happening now, so stay tuned.
Why I Don’t Recommend Fasting for People With CKD
Some of that research sounds exciting, and I get why fasting is tempting. But when I look at the full picture, fasting just isn’t a good fit for most people with kidney disease.
The Research Isn’t There Yet
Most of the promising results come from animal studies or small, short studies in people.
We don’t know what happens to kidney health when people fast for months or years.
Fasting Leaves Less Room for Kidney-Friendly Foods
Fruits, vegetables, whole grains, and beans are some of the most powerful tools for kidney health. When you squeeze your eating into fewer hours or fewer days, there’s less room for all of them.
It also gets harder to spread protein and fiber across your day and get enough to keep your muscles strong and avoid digestive issues. Every meal has to do more work.
It Adds More Food Rules and Stress
If every meal already feels like a test, a fasting schedule just adds another set of rules. Now it’s not only what you eat, but when you’re allowed to eat it.
Kidney nutrition works best when it feels flexible and doable in real life. Fasting usually feels like the opposite.
The Risks Outweigh the Possible Benefits
With CKD, fasting can lead to;
- Dehydration
- Muscle loss
- Potassium changes
- Problems with medicines
For most people, those risks aren’t worth a small, uncertain benefit.
The Risks of Fasting With Kidney Disease
This is the part a lot of fasting videos skip. Here’s what to keep an eye on.
Dehydration and Sudden Kidney Injury
Going without water for many hours can lower blood flow to your kidneys. With CKD, that raises the risk of a sudden drop in kidney function, called acute kidney injury (AKI) (16).
This risk is highest with fasts that don’t allow water. It also goes up in later stages of CKD.
Not Getting Enough Protein and Calories
Your body still needs fuel, even with kidney disease. Cutting back too far for too long can lead to muscle loss and malnutrition.
This is called protein-energy wasting (12). It’s a bigger concern in later stages of CKD, when nutrition needs extra care.
Changes in Potassium
Fasting can shift potassium and other minerals in your blood. This is a bigger concern for people on dialysis.
During a fast, insulin levels drop, which can push potassium out of your cells and into your blood (17). High potassium can affect your heart rhythm.
Medicine Timing
Fasting can change how and when your medicines work. This includes blood pressure medicines, water pills (diuretics), SGLT2 inhibitors, and diabetes medicines.
Some diabetes medicines can also cause low blood sugar when you’re not eating. Please don’t change any medicines on your own.
Fasting With Diabetes and Kidney Disease
Diabetes is one of the most common causes of kidney disease, so this question comes up a lot. With diabetes, fasting brings a few extra concerns.
What the Research Shows for Diabetic Kidney Disease
In one 6-month study, 40 people with type 2 diabetes and kidney damage tried either a monthly fasting-mimicking diet or a Mediterranean-style diet (18). Overall, the fasting group didn’t do any better at lowering protein in the urine.
The only drop showed up in people with smaller amounts of protein leaking to begin with. People with larger amounts saw no benefit.
The fasting group also had better insulin sensitivity during the study. But that was the only benefit still there after the study ended.
What Animal Studies Are Showing
In diabetic mice, a fasting-mimicking diet lowered protein in the urine (19). But most of the weight they lost was muscle and water, not fat.
The mice also showed more signs of stress in the kidney’s filters. That raises real questions about repeating this kind of fasting with diabetes.
Low Blood Sugar Is the Biggest Concern
With diabetes, the main danger of fasting is low blood sugar (hypoglycemia). In one comparison, people with type 2 diabetes had more low blood sugar episodes with intermittent fasting than with simply eating fewer calories (20).
That happened even when their medicines were adjusted. Fasting can also make blood sugar swing up and down, and those swings are linked to more diabetes complications over time.
Dehydration Adds to the Risk
The kidney risks of fasting still apply with diabetes. Fasts without water, plus medicines that affect blood flow to the kidneys, can raise the chance of a sudden kidney injury.
What Diabetes Guidelines Say
No major diabetes or kidney group recommends fasting as a treatment for diabetic kidney disease. For religious fasts like Ramadan, the American Diabetes Association calls for a risk check and medicine planning well ahead of time (21).
The Takeaway for Diabetic Kidney Disease
In that 6-month study, fasting didn’t beat a Mediterranean-style way of eating overall (18). You don’t need to fast to support your kidneys and blood sugar.
Who Faces the Highest Risk From Fasting?
Fasting isn’t my recommendation for anyone with CKD. But for some people, the risks are even higher.
Stage 4 or 5 CKD
The risk of dehydration and sudden kidney injury goes up in later stages. This is especially true with fasts that don’t allow water.
Dialysis
Fasting can raise potassium levels and make fluid balance harder to manage. Your dialysis dietitian and care team should guide any changes to when you eat.
A Recent Drop in Kidney Function
If you recently had a sudden kidney injury, or your eGFR has been dropping, fasting adds stress your kidneys don’t need. Focus on steady, nourishing meals instead.
Low Appetite or Unplanned Weight Loss
If you’re already struggling to eat enough, fasting can make it even harder. The same goes if you’ve been told you’re low in protein or muscle.
Diabetes Medicines That Lower Blood Sugar
Some diabetes medicines can cause low blood sugar when you skip meals. Talk with your doctor before changing when or how often you eat.
If One of These Sounds Like You
This doesn’t mean you’re doing anything wrong. It just means fasting carries even more risk for you right now.
There are so many other ways food can support your kidneys. Do everything within your power, and know that fasting doesn’t need to be part of it.
Fasting for Religious Reasons With Kidney Disease
For many people, fasting is a meaningful part of their faith. If that’s you, I respect that, and I want to help you do it as safely as possible.
Many faith traditions also make room for people with health conditions. If you’re unsure, it may help to talk with your faith leader along with your healthcare team.
Step 1: Talk to Your Nephrologist and Kidney Dietitian Before the Fast
Ideally, start these conversations 1 to 3 months ahead. Your team can look at your stage, labs, and medicines to help you decide if fasting is safe for you this time.
If you have diabetes, your doctor may also use a diabetes-specific risk tool before the fast (21). It helps sort out whether your risk is low, moderate, or high.
Step 2: Get Labs Before, During, and After
Experts suggest labs before the fast, a check-in during the first week, and follow-up afterward (10). Creatinine, eGFR, and potassium are key ones to watch.
Your eGFR will always bounce around a little. But a change of more than 20% is bigger than normal ups and downs, so let your doctor know right away (22).
Step 3: Ask Your Doctor About Your Medicines
Please don’t change any medicines on your own. Your doctor may need to adjust the timing or dose to fit your fasting schedule, including medicines like SGLT2 inhibitors.
With diabetes, insulin and sulfonylureas carry the highest risk of low blood sugar during a fast. Ask about changes well before the fast starts, not the week of.
Step 4: Make Your Pre-Dawn and Evening Meals Count
With fewer meals, each one matters more. Build your plate around vegetables, fruits, whole grains, and beans, plus enough protein to keep your muscles strong.
Go easy on salty foods, since they can make you thirstier during the fasting hours ahead.
Step 5: Rehydrate During Non-Fasting Hours
Spread your fluids out between sunset and sunrise instead of drinking a lot at once. If you have a fluid limit, stick with the amount your doctor recommends.
Step 6: If You Have Diabetes, Check Your Blood Sugar More Often
Check more often than usual while fasting, especially in the last few hours before sunset. About half of low blood sugar episodes happen in that window (20).
Save hard exercise for after you break your fast. That’s when your body has fuel again.
Step 7: Know the Signs It’s Time to Break Your Fast
Break your fast and call your healthcare team if you feel dizzy, weak, very thirsty, or crampy. The same goes for swelling, peeing much less than usual, or a racing or skipping heartbeat.
If you have diabetes, shakiness, sweating, or confusion can be signs of low blood sugar. Break your fast and treat it the way your care team showed you.
What I Recommend Instead
You don’t need to fast to protect your kidneys. Here’s what I’d focus on instead.
Add Before You Take Away
It’s not about restriction; it’s about addition. Adding more fruits, vegetables, whole grains, and beans supports your kidneys without cutting out the foods you love.
Eat Regular, Balanced Meals
Spreading meals across your day makes it easier to get the nutrition you need. A simple start is filling half your plate with vegetables, then adding a whole grain and a protein.
Eat More of Your Food Earlier in the Day
You don’t need a strict eating window to benefit from good timing. Try making breakfast and lunch your bigger meals, with a lighter dinner.
Eating earlier lines up with your body’s natural clock and may help with blood sugar and blood pressure. If late-night snacking is a habit, that’s a simple place to start.
Mix Plant and Animal Proteins
Try about half your usual meat portion (around 2 ounces) and swap the other half for a plant protein. Beans, lentils, and tofu are all great options.
Enjoy Your Favorite Foods in Kidney-Friendly Portions
Very few foods are completely off the table with CKD. Portions and balance usually matter more than cutting things out.
Keep a Food Journal
A food journal shows you what you’re actually eating, not what you think you’re eating. It’s one of the best ways to find simple changes that make a real difference.
Fasting and Kidney Disease FAQ
Does Fasting Protect Your Kidneys?
There’s no strong proof that it does. A few small studies show interesting results, but they’re not enough to recommend fasting for kidney health.
Is Fasting Good for Diabetic Kidney Disease?
The research doesn’t show a clear benefit, and fasting raises the risk of low blood sugar. In the best study so far, fasting didn’t do any better overall than a Mediterranean-style diet (18).
Is Intermittent Fasting a Good Way to Lose Weight With CKD?
People in the 16:8 study did lose weight, but other factors may have played a role in their results (such as getting an average of about 7,500 steps per day).
There are gentler ways to get there. Slow and steady is the goal, because losing weight too fast can mean losing muscle.
Keep your protein steady and talk with your kidney dietitian about a healthy pace.
Is It OK to Skip Breakfast With Kidney Disease?
If you’re truly not hungry in the morning, that may be okay (but check with your doctor or dietitian to be safe).
Eating earlier in the day lines up better with your body’s natural clock, and regular meals make it easier to fit in more fruits, vegetables, and whole grains.
Is It Bad to Eat Late at Night With Kidney Disease?
It’s not “bad,” but timing may matter. Research links eating most of your food later in the day with higher odds of diabetic kidney disease and more protein in the urine (6).
Additionally, your food choices may be a sign of something more. If you are craving high-calorie foods, your body may be trying to make up for not getting enough earlier in the day.
Those studies show a link, not proof. Still, shifting more of your eating earlier is a simple, flexible change that doesn’t require fasting.
Can I Drink Water During a Religious Fast?
Ramadan and many other sunrise-to-sunset fasts don’t allow water during the day. That’s why rehydrating well between sunset and sunrise is so important, unless you have a fluid limit.
That’s also why it’s important to discuss any fasting with your physician or nephrologist first, so they can discuss a plan with you to help keep your kidneys safe.
What Should I Eat Before and After a Religious Fast?
Aim for a balanced, kidney-friendly plate at both meals. Fill about half your plate with vegetables, then add a whole grain and a protein.
Mixing plant proteins like beans, lentils, or tofu with smaller portions of meat helps you get enough protein.
Go easy on salty foods, which can make fasting hours harder.
The Bottom Line
Fasting is an interesting area of kidney research, but it’s still early. Right now, there isn’t enough evidence to recommend it for people with kidney disease.
So those claims that fasting “protects” your kidneys? They’re getting ahead of what the science can actually show.
If you fast for religious reasons, work closely with your nephrologist and kidney dietitian. Close monitoring makes all the difference.
For everyone else, protecting your kidneys isn’t about eating less or eating less often. It’s about finding the most flexible ways to enjoy food while supporting your kidney health.
If you’re tired of guessing what belongs on your plate, my free class, Unlocking Kidney Nutrition, will show you how to use a food journal to find simple, kidney-friendly changes that fit your real life. 💚
Save your spot in the free Unlocking Kidney Nutrition class
Jen Hernandez is a registered dietitian, board-certified specialist in renal nutrition, and author of Plant-Powered Kidney Nutrition: Proven Methods and Easy Recipes to Support Your Kidney Health (available on Amazon). She has nearly a decade of experience with kidney disease patients in all stages - from stage 1 through kidney transplant. Jen writes on the blog of Plant-Powered Kidneys to help reach and teach more kidney patients about how they can enjoy more foods in a plant-based diet while protecting kidney health.
