Nutrition Diet: How many calories to eat during intermittent fasting 20/4?

October 16, 2025 •

4 min read

Research shows that people can naturally reduce their daily calorie intake by approximately 550 calories when following a 20/4 intermittent fasting schedule. However, to truly optimize results and health, understanding how many calories to eat during intermittent fasting 20/4 is crucial, as this number is unique to every individual.

Quick Summary

Calorie needs for 20/4 intermittent fasting are personalized and depend on your body's energy expenditure. The goal is to consume 85–90% of your total daily calories in a compressed 4-hour window by focusing on nutrient-dense foods.

Key Points

Calculate Your Needs: Use a TDEE calculator based on your BMR to estimate your daily calorie needs for maintenance.
Target 85–90%: During your 4-hour eating window, aim to consume 85–90% of your total daily calorie target.
Prioritize Nutrient-Dense Foods: Focus on lean proteins, healthy fats, and fiber-rich carbohydrates within your eating window to avoid deficiencies.
Hydrate, Hydrate, Hydrate: Stay hydrated throughout the 20-hour fast with water, black coffee, or herbal tea, and consider electrolyte supplements.
Break the Fast Gently: Start your eating window with easy-to-digest foods like broth or eggs to prevent digestive issues.
Listen to Your Body: The 20/4 method is intense. Monitor for fatigue, headaches, or mood changes, and adjust your approach if necessary.
Plan Your Meals: Strategic meal planning helps ensure you meet nutritional goals and avoid unhealthy choices during your compressed eating time.

The 20/4 intermittent fasting protocol, sometimes called the Warrior Diet, involves a daily 20-hour fasting period followed by a 4-hour eating window. Unlike simpler fasting methods, this is a more advanced approach that requires careful planning to ensure nutritional needs are met while maintaining a calorie deficit for weight loss, if that is the goal. The key is not to view the 4-hour window as a free-for-all but rather a strategic period for consuming the majority of your day's calories from quality sources.

Calculating Your Daily Calorie Target

Determining your specific calorie target is the first and most critical step. This is a personalized number based on your body's energy requirements, and it involves two main calculations.

Step 1: Calculate Your Basal Metabolic Rate (BMR)

Your BMR is the energy your body needs to perform basic, life-sustaining functions at rest. The Mifflin-St Jeor equation is one of the most widely used methods:

Men: $(10 imes ext{weight in kg}) + (6.25 imes ext{height in cm}) - (5 imes ext{age in years}) + 5$
Women: $(10 imes ext{weight in kg}) + (6.25 imes ext{height in cm}) - (5 imes ext{age in years}) - 161$

Step 2: Determine Your Total Daily Energy Expenditure (TDEE)

Your TDEE is your BMR adjusted for your daily activity level. This is the estimated number of calories you need to consume to maintain your current weight.

Sedentary (little to no exercise): BMR x 1.2
Lightly active (light exercise 1–3 days/week): BMR x 1.375
Moderately active (moderate exercise 3–5 days/week): BMR x 1.55
Very active (hard exercise 6–7 days a week): BMR x 1.725
Super active (very hard exercise & physical job): BMR x 1.9

Step 3: Set Your 20/4 Calorie Goal

For weight loss, a typical calorie deficit is 200–500 calories below your TDEE. However, the original Warrior Diet approach suggests consuming 85–90% of your daily calorie needs within the 4-hour window, relying on the natural calorie reduction that the shorter eating period often encourages. A simple approach is to aim for your TDEE minus a moderate deficit and consume that total during your eating window.

The Role of Macronutrients and Nutrient Density

With only a 4-hour window to eat, the quality and type of food you consume are paramount. Prioritizing nutrient-dense, whole foods prevents malnutrition and supports energy levels throughout your fast.

Proteins: Crucial for muscle repair and satiety. Lean meats, fish, eggs, and legumes are excellent choices.
Healthy Fats: Provide a sustained energy source and help with satiety. Sources include avocados, nuts, seeds, and olive oil.
Fiber-Rich Carbohydrates: Whole grains, fruits, and vegetables provide essential vitamins, minerals, and fiber, which aids digestion.

Example Meal Ideas for the 20/4 Window

Eating one large meal or two smaller meals within the 4-hour window is possible. Here are some ideas for a nutrient-dense approach:

Meal 1 (e.g., 4:00 PM): A large, colorful salad topped with a lean protein source like grilled chicken or chickpeas, healthy fats from a vinaigrette or avocado, and plenty of mixed vegetables.
Meal 2 (e.g., 7:00 PM): Baked salmon with a side of quinoa and steamed broccoli. Finish with a small bowl of berries and Greek yogurt for dessert.

Comparison of Fasting Schedules

To put the 20/4 approach in perspective, here's how it compares to the more common 16/8 method.


Feature	20/4 Intermittent Fasting (Warrior Diet)	16/8 Intermittent Fasting
Eating Window	4 hours	8 hours
Fasting Window	20 hours	16 hours
Calorie Intake	Typically 85–90% of daily calories within the window.	Spread throughout the 8-hour window.
Restrictiveness	More restrictive and challenging; often for experienced fasters.	Easier and more sustainable for beginners.
Potential Benefits	Deeper fat-burning, enhanced autophagy, faster weight loss.	More gradual fat loss, easier to sustain long-term.
Nutritional Focus	Intense focus on nutrient density in the compressed window.	Easier to meet nutrient needs over a longer period.

Breaking the Fast Safely

Breaking a 20-hour fast requires a gentle approach to avoid digestive discomfort. Your digestive system has been resting, and a large, heavy meal right away can be a shock to your system.

Best Practices for Breaking Your Fast:

Start Small: Begin with a small portion of easily digestible food.
Focus on Nutrient-Dense Foods: Choose foods like bone broth, fermented foods (yogurt, kefir), hard-boiled eggs, or a simple vegetable soup.
Stay Hydrated: Water is critical. Consider adding electrolytes to your water to replenish lost minerals.
Avoid: Immediately consuming high-sugar, high-fat, or heavily processed foods. These can cause a blood sugar spike and digestive upset.

Conclusion

Figuring out how many calories to eat during intermittent fasting 20/4 is a process that begins with understanding your individual TDEE and involves strategic meal planning. By consuming the majority of your daily calorie needs within the 4-hour window and focusing on nutrient-dense foods, you can leverage the benefits of this advanced fasting protocol for fat loss, improved insulin sensitivity, and enhanced metabolic health. Always listen to your body and prioritize overall nutrition over simple calorie counting to ensure long-term, sustainable success. For more in-depth information on the scientific benefits of intermittent fasting, research from reputable sources like Johns Hopkins Medicine is available.

Essential Hydration During Your 20-Hour Fast

Staying properly hydrated is perhaps the most important aspect of a successful 20/4 fast. Water, black coffee, and unsweetened teas are all acceptable and can help manage hunger and fatigue. Many people also benefit from adding electrolyte supplements to their water to replace minerals lost during the fasting period.

Risks and Considerations

While effective for many, the 20/4 protocol is not suitable for everyone. It is more restrictive and carries a higher risk of malnutrition if not properly planned. Individuals who are new to fasting should start with a less aggressive schedule, like 16/8, and gradually increase their fasting time. Those with pre-existing medical conditions, including diabetes, or individuals who are pregnant or breastfeeding, should consult a healthcare professional before beginning any fasting regimen.

Frequently Asked Questions

First, calculate your Basal Metabolic Rate (BMR) using an online calculator with your weight, height, age, and sex. Next, multiply your BMR by an activity factor to get your Total Daily Energy Expenditure (TDEE). Finally, consume 85–90% of this TDEE number during your 4-hour eating window.

If you consistently eat more calories than your body burns in a day, you will not achieve weight loss, even with a 20-hour fasting window. The key to weight loss is a sustainable calorie deficit, which requires portion control and mindful eating within the 4-hour period.

Focus on nutrient-dense, whole foods. This includes lean proteins (chicken, fish, tofu), healthy fats (avocado, nuts, seeds), and complex carbohydrates from vegetables, fruits, and whole grains.

While strict calorie counting isn't always necessary for weight loss, it can be beneficial, especially with a short eating window. Tracking can ensure you meet your nutritional needs and maintain a calorie deficit. Focusing on balanced, wholesome foods is the most important aspect.

Some variations of the Warrior Diet allow small amounts of low-calorie foods like raw fruits, vegetables, or hard-boiled eggs during the 20-hour fast. However, most intermittent fasting protocols prohibit any calories during the fasting window, allowing only water, black coffee, and unsweetened tea.

Break your fast gently by starting with easily digestible, nutrient-rich foods. Good options include bone broth, eggs, yogurt, or a simple smoothie. Avoid immediately eating large, heavy, or highly processed meals.

Common side effects, especially in the beginning, can include hunger, fatigue, headaches, and irritability. Staying hydrated with water and electrolytes can help mitigate some of these symptoms.