Intermittent fasting: What is it, and how does it work?

Intermittent fasting (IF) is not just a diet—it’s a lifestyle that focuses on when you eat rather than what you eat. Unlike calorie-restricted diets that often feel restrictive, intermittent fasting alternates between periods of eating and fasting. This natural rhythm allows your body to use energy more efficiently, promote fat loss, and improve cellular health.

For centuries, fasting has been part of cultural, religious, and healing traditions. Today, modern science has begun to validate what ancient practices have always believed: fasting has profound health benefits when practiced correctly.

How Intermittent Fasting Works

When you eat, your body breaks down food into glucose, which is used as the primary source of energy. Any excess glucose is stored as glycogen in the liver and muscles, or as fat.

During fasting:

• Once glucose reserves are depleted, your body shifts to burning stored fat.

• This process triggers ketosis, where ketone bodies become the main source of fuel.

• Over time, fasting enhances metabolism, improves insulin sensitivity, and promotes cellular repair.

The Timeline of Intermittent Fasting: What Happens Hour by Hour

Hour 12 – Getting There

After 12 hours without food, your body has mostly used up glucose from your last meal. At this stage:

• Blood sugar levels are stable.

• Your body is still running on glycogen reserves.

• Fat burning has not fully started yet.

Hour 16 – Fat Burning Begins

At the 16-hour mark:

• Glycogen reserves deplete further.

• Your body starts mobilizing fat stores for energy.

• Growth hormone levels rise, preserving muscle mass.

• Exercise at this stage enhances fat burning significantly.

Hour 18 – The Fasting “Sweet Spot”

Many intermittent fasting schedules (like 18:6) end here. However:

• Fat burning intensifies.

• Insulin levels drop further, reducing fat storage.

• Cellular repair processes begin, clearing out damaged cells.

Hour 20 – Peak Fat Burn Zone

Now, the body becomes a fat-burning machine:

• Ketosis begins, especially for those following low-carb diets.

• Mental clarity improves due to stable ketone energy.

• Inflammation starts to decrease.

Hour 24 – Ketosis Kickoff

Reaching 24 hours unlocks powerful health benefits:

• Autophagy (cellular self-cleaning) begins.

• Damaged proteins are recycled.

• The body experiences rejuvenation at a cellular level.

Popular Intermittent Fasting Methods

There are several ways to practice intermittent fasting, depending on individual goals:

1. 16:8 Method

   • Fast for 16 hours, eat during an 8-hour window.

   • Example: Eat between 12 PM – 8 PM.

   • Best for beginners.

2. 18:6 Method

   • Fast for 18 hours, eat in a 6-hour window.

   • Example: Eat between 1 PM – 7 PM.

   • Enhances fat-burning benefits.

3. 20:4 Method (Warrior Diet)

   • 20 hours fasting, 4-hour eating window.

   • Typically used by advanced practitioners.

4. 5:2 Fasting

   • Eat normally for 5 days.

   • Restrict calories to 500–600 for 2 days.

5. 24-Hour Fast (Eat-Stop-Eat)

   • Complete fast for one or two days per week.

   • Promotes strong cellular repair processes.

Health Benefits of Intermittent Fasting

1. Weight Loss and Fat Burning

• Fasting lowers insulin levels, encouraging fat breakdown.

• Increased growth hormone preserves lean muscle mass.

2. Improved Insulin Sensitivity

• Helps regulate blood sugar levels.

• Beneficial for people with prediabetes or Type 2 diabetes.

3. Heart Health

• Reduces cholesterol and triglyceride levels.

• Improves blood pressure.

4. Brain Function

• Boosts brain-derived neurotrophic factor (BDNF).

• Enhances memory and focus.

5. Cellular Repair & Longevity

• Autophagy helps prevent neurodegenerative diseases.

• May slow down aging at the cellular level.

6. Inflammation Reduction

• Decreases oxidative stress.

• Promotes healing and immune balance.

Who Should Avoid Intermittent Fasting?

While IF has many benefits, it is not suitable for everyone. You should avoid or consult a doctor if you are:

• Pregnant or breastfeeding.

• Underweight or have eating disorders.

• Diabetic and on insulin therapy.

• A child or teenager still growing.

• Someone with chronic health conditions.

Tips for a Successful Intermittent Fasting Journey

1. Stay Hydrated – Drink water, herbal teas, or black coffee.

2. Start Slow – Begin with 12:12 or 14:10 before moving to longer fasts.

3. Eat Nutrient-Dense Foods – Break your fast with whole foods, not junk.

4. Exercise Smartly – Light workouts during fasting enhance fat burn.

5. Listen to Your Body – Don’t push beyond your limits.

Intermittent Fasting and Diagnostics

Before starting intermittent fasting, it’s advisable to check your blood sugar, lipid profile, and kidney function to ensure it’s safe for your body.

👉 At Sparsh Diagnostic Centre, you can get:

• Lipid Profile Test – to monitor cholesterol.

• Kidney Function Test (KFT) – to assess renal health.

• Blood Sugar Tests – to check fasting and post-meal glucose.

Sparsh also offers home sample collection facilities across Kolkata, making it convenient to track your health while fasting.

Frequently Asked Questions (FAQ)

Q1: How long should I fast for best results?
Most people see results with 16:8 fasting. However, extending to 18–20 hours provides stronger fat-burning and cellular benefits.

Q2: Can I drink water during intermittent fasting?
Yes! Water, black coffee, and unsweetened herbal tea are allowed. They don’t break your fast.

Q3: Will intermittent fasting slow my metabolism?
No. In fact, short-term fasting boosts metabolism by increasing norepinephrine and growth hormone levels.

Q4: Can intermittent fasting help with diabetes?
Yes, but it must be supervised by a doctor, especially for those on insulin or medication.

Q5: What should I eat to break a fast?
Go for light, nutrient-rich foods like fruits, vegetables, soups, eggs, and lean protein. Avoid fried and processed foods.

Q6: Is intermittent fasting safe for women?
Yes, but women may respond differently. Shorter fasting windows (14:10 or 12:12) may be more suitable.

Q7: How soon will I see results?
Weight loss and improved energy can be noticed within 2–4 weeks, but benefits like improved insulin sensitivity may take longer.

Intermittent fasting is more than a trend—it’s a powerful lifestyle strategy that can transform your health. By understanding how your body responds hour by hour, you can unlock benefits ranging from fat burning to cellular rejuvenation.

If you’re planning to start intermittent fasting, consider getting baseline health tests at Sparsh Diagnostic Centre to ensure it’s safe and effective for you.