Intermittent Fasting and Kidney Health: Benefits, Risks, and What the Science Says

What Is Intermittent Fasting and How Does It Work?

Intermittent fasting (IF) is not a diet but rather an eating pattern that cycles between periods of fasting and eating. Unlike traditional diets that focus on what to eat, intermittent fasting centres on when to eat. This approach has ancient roots in human evolution and various religious practices, but has recently gained scientific attention for its potential health benefits.

Common Intermittent Fasting Methods

• The 16/8 Method: Restricting eating to an 8-hour window daily while fasting for 16 hours
• The 5:2 Diet: Eating normally five days a week while limiting calories to 500-600 on two non-consecutive days
• Eat-Stop-Eat: Incorporating one or two 24-hour fasts per week
• Alternate-Day Fasting: Alternating between normal eating days and fasting or very low-calorie days

Primary Health Goals of Intermittent Fasting

People adopt intermittent fasting for various health objectives, including:

When you fast, your body undergoes several metabolic changes. After depleting glucose stores (typically within 8-12 hours of fasting), your body shifts to burning stored fat for energy. This metabolic switch can trigger various cellular processes that may influence kidney function, either positively or negatively, depending on individual health factors.

Conflicting Claims: Does Intermittent Fasting Help or Harm Kidneys?

The scientific community remains divided on whether intermittent fasting benefits or harms kidney health. This division stems from conflicting research findings and the complex relationship between fasting, metabolism, and kidney function.

A 2021 study published in the journal Kidney International found that intermittent fasting reduced albuminuria (protein in urine) in patients with type 2 diabetes and diabetic nephropathy. However, these benefits disappeared once participants returned to their normal eating patterns, suggesting that consistent fasting might be necessary for sustained kidney benefits.

Conversely, a 2017 study of 65 adults with stage 3 or higher CKD found that fasting during Ramadan was associated with worsened kidney function. Yet other studies have found no negative effects of similar fasting patterns on kidney health, highlighting the need for more research in this area.

How Intermittent Fasting Affects Kidney Function: 5 Key Mechanisms

Understanding the biological mechanisms behind intermittent fasting’s effects on kidney function helps explain the conflicting research findings. Here are five key ways intermittent fasting might influence your kidneys:

1. Autophagy and Cellular Repair

Intermittent fasting triggers autophagy, a process where cells remove damaged components and regenerate healthier ones. In kidney cells, enhanced autophagy may help clear damaged proteins and organelles, potentially slowing kidney disease progression. A 2020 study published in Cell Metabolism demonstrated that fasting-induced autophagy reduced kidney damage in mouse models of polycystic kidney disease.

2. Blood Pressure Regulation

Hypertension is a leading cause of kidney damage. Intermittent fasting may help regulate blood pressure through weight loss, improved insulin sensitivity, and reduced inflammation. A 2023 systematic review in Nutrients found that various intermittent fasting protocols reduced systolic and diastolic blood pressure in most participants, which could indirectly benefit kidney health.

3. Metabolic Pathway Alterations

During fasting, the body shifts from using glucose to ketones for energy. This metabolic switch affects various signalling pathways that influence kidney function. Research published in the Journal of Clinical Investigation suggests that ketone bodies produced during fasting may protect against acute kidney injury by reducing oxidative stress and inflammation in kidney tissues.

4. Electrolyte Balance and Hydration

Fasting periods can affect fluid and electrolyte balance, which directly impacts kidney workload. Without adequate hydration during eating windows, the kidneys must work harder to maintain proper electrolyte levels and filter more concentrated waste products. This increased workload could potentially stress the kidneys, especially in those with existing kidney issues.

5. Inflammation Reduction

Chronic inflammation contributes to kidney disease progression. Intermittent fasting has been shown to reduce inflammatory markers like C-reactive protein, TNF-alpha, and IL-6. A 2022 study in the American Journal of Physiology-Renal Physiology found that intermittent fasting reduced kidney inflammation in animal models of diabetic nephropathy.

Recent Clinical Evidence: What Studies Show About IF and Kidney Biomarkers

Recent clinical studies (2020-2024) have provided new insights into how intermittent fasting affects key kidney biomarkers. These biomarkers help assess kidney function and include measurements like creatinine levels, estimated glomerular filtration rate (egfr), and protein in urine (proteinuria).

Consensus Areas in Research

Despite some conflicting findings, researchers generally agree on several points:

• Short-term intermittent fasting (up to 16 hours) appears safe for individuals with normal kidney function
• Adequate hydration during eating windows is crucial for kidney protection during fasting
• Weight loss resulting from intermittent fasting may indirectly benefit kidney health
• Benefits appear most pronounced in those with metabolic conditions like diabetes and obesity
• Effects of fasting on kidney biomarkers often disappear when normal eating patterns resume

Unresolved Questions

Several important questions remain unanswered in the current research:

• Which intermittent fasting protocol is optimal for kidney health?
• How do individual factors like age, sex, and ethnicity influence kidney responses to fasting?
• What is the long-term impact (5+ years) of intermittent fasting on kidney function?
• Can intermittent fasting slow progression in those already diagnosed with kidney disease?
• How should medication schedules be adjusted during fasting periods for those with kidney conditions?

Practical Advice: Is Intermittent Fasting Right for Your Kidney Health?

Whether intermittent fasting is appropriate for you depends largely on your current kidney health status, other medical conditions, and individual risk factors. Here’s actionable advice for different groups:

For People with Healthy Kidneys

• Start with shorter fasting periods (12-14 hours) before attempting longer fasts
• Maintain adequate hydration during eating windows
• Monitor for symptoms like excessive fatigue, dizziness, or changes in urination
• Consider regular kidney function tests if practising intermittent fasting long-term
• Focus on nutrient-dense foods during eating windows to support kidney health

For People with Chronic Kidney Disease (CKD)

• CKD stages 1-2 with stable function: May consider gentle time-restricted eating (10-12 hour eating window) with close monitoring
• CKD stages 3-5: Generally advised against longer fasting periods; focus on consistent meal timing and kidney-friendly nutrition
• Transplant recipients: Typically should avoid intermittent fasting due to medication timing requirements
• Dialysis patients: Should not practice intermittent fasting without specific medical guidance

For People with Diabetes

Diabetes is a leading cause of kidney disease, making this group particularly important to address:

• Work closely with your healthcare provider to adjust medication timing and dosages
• Monitor blood glucose more frequently when fasting
• Consider shorter fasting windows (12-14 hours) to start
• Be alert for hypoglycemia symptoms, which can be more common during fasting
• Regular kidney function tests are especially important for this group

For People with Hypertension

High blood pressure is another major risk factor for kidney disease:

• Monitor blood pressure regularly when practising intermittent fasting
• Maintain consistent medication schedules, which may require adjusting fasting windows
• Focus on sodium reduction during eating periods
• Consider the 16/8 method, which has shown blood pressure benefits in some studies

Safe Fasting Practices for Kidney Health

Regardless of your kidney health status, these practices can help minimise risks:

• Hydration: Drink 6-8 glasses of water during eating windows
• Electrolyte balance: Include potassium, magnesium, and sodium-containing foods as appropriate for your condition
• Gradual approach: Extend fasting periods gradually rather than jumping into extended fasts
• Quality nutrition: Focus on nutrient-dense, kidney-friendly foods during eating windows
• Regular monitoring: Track kidney function biomarkers if practising intermittent fasting long-term

Conclusion: Balancing the Evidence on Intermittent Fasting and Kidney Health

The relationship between intermittent fasting and kidney health is nuanced and highly individualised. Current research suggests that while intermittent fasting may offer benefits for some people, particularly those with obesity, diabetes, or early-stage kidney issues, it may pose risks for others, especially those with advanced kidney disease or specific medical conditions.

As research continues to evolve, our understanding of how intermittent fasting affects kidney health will become clearer. For now, a cautious, personalised approach under appropriate medical guidance represents the most prudent path forward.

Remember that intermittent fasting is just one potential tool in a comprehensive approach to kidney health. Other factors—including overall diet quality, physical activity, blood pressure management, and medication adherence—remain foundational to protecting your kidneys over the long term.

Always consult with your healthcare provider before starting any fasting regimen, especially if you have existing kidney concerns or conditions that affect kidney function. Your provider can help you weigh the potential benefits against the risks based on your specific health profile.