How to Calculate Calories for Intermittent Fasting

Are you wondering how to navigate the balance between fasting and eating to support your weight loss goals? Intermittent fasting (IF) might seem straightforward—eat during certain hours and fast for the rest—but what happens during those eating windows can make or break your success. To truly benefit from IF, understanding how to calculate your caloric intake is crucial.

Getting it right isn’t about cutting calories to the bone. Instead, it’s about ensuring you fuel your body properly during your eating periods, so you don’t just lose weight but also maintain energy, muscle mass, and overall well-being. This balance requires a bit of math and a lot of listening to your body, but once you have a handle on it, the results can be incredibly rewarding.

Key Takeaways:

• Understand Your Body’s Needs: Know your baseline calorie needs before starting IF.

• Don’t Skimp on Calories: Eating too little can be just as harmful as overeating.

• Tailor Your Intake: Adjust based on your specific fasting schedule and activity level.

• Sustainable Approach: Gradually extend fasting periods to give your body time to adapt.

Let’s dive into how to calculate those all-important calories and set yourself up for intermittent fasting success.

Table of Contents

How to calculate intermittent fasting: all you need to know

To determine the right calorie intake during intermittent fasting, it’s crucial to balance your nutritional needs with your fasting schedule. Here’s a detailed breakdown:

Calculate Your Basal Metabolic Rate (BMR)

Your BMR represents the number of calories your body needs to maintain basic functions like breathing and digestion while at rest. You can calculate this using the Harris-Benedict equation:

 - For men: 

   $$
   BMR = 88.362 + (13.397 \times \text{weight in kg}) + (4.799 \times \text{height in cm}) - (5.677 \times \text{age in years})
   $$
 - For women: 
   $$
   BMR = 447.593 + (9.247 \times \text{weight in kg}) + (3.098 \times \text{height in cm}) - (4.330 \times \text{age in years})
   $$

Factor in Your Activity Level

• Multiply your BMR by an activity factor:
• Sedentary (little or no exercise): BMR × 1.2
• Lightly active (light exercise/sports 1-3 days a week): BMR × 1.375
• Moderately active (moderate exercise/sports 3-5 days a week): BMR × 1.55
• Very active (hard exercise/sports 6-7 days a week): BMR × 1.725
• Super active (very hard exercise/sports & physical job): BMR × 1.9

Determine Your Caloric Needs During Eating Windows

Once you have your Total Daily Energy Expenditure (TDEE), this will be the benchmark for your calorie intake during eating periods. Ensure your total calorie consumption during the eating window doesn’t fall below this threshold to maintain energy levels and support metabolic functions.

Adjust According to Fasting Goals

If your goal is weight loss, aim for a moderate calorie deficit, typically 10-20% below your TDEE. However, avoid extreme deficits as they can lead to nutrient deficiencies and metabolic slowdown.

Monitor and Adjust

Regularly monitor your progress and energy levels. If you experience fatigue, irritability, or prolonged hunger, consider recalibrating your calorie intake.

How to get started with intermittent fasting?

To begin intermittent fasting, it’s essential to follow a structured approach that eases you into the practice while ensuring you’re making informed and sustainable choices. Here’s a detailed guide on the first steps:

How to calculate calories for intermittent fasting

To determine your daily calorie needs while practicing intermittent fasting (IF), follow these steps:

Calculate Your Basal Metabolic Rate (BMR)

This is the number of calories your body needs at rest to maintain basic physiological functions like breathing and circulation. Use the Mifflin-St Jeor equation, which is widely accepted:

• For men:

$$BMR = (10 \times \text{weight in kg}) + (6.25 \times \text{height in cm}) - (5 \times \text{age in years}) + 5$$

• For women:

$$BMR = (10 \times \text{weight in kg}) + (6.25 \times \text{height in cm}) - (5 \times \text{age in years}) - 161$$

Determine Your Total Daily Energy Expenditure (TDEE)

Multiply your BMR by an activity factor to estimate the total calories burned daily. The activity factors are:

Example: If you have a BMR of 1,500 kcal and are moderately active, your TDEE would be:

$$TDEE = 1,500 \times 1.55 = 2,325 \text{ kcal/day}$$

Adjust Calories for Weight Goals

If your goal is weight loss, aim to consume fewer calories than your TDEE. A common recommendation is to reduce your intake by 15-20% of your TDEE.

For weight maintenance, match your calorie intake with your TDEE. For muscle gain, increase your calorie intake by 10-15%.

Consider the Fasting Window

While you may fast for 16 hours (e.g., using the 16/8 method), ensure that during your 8-hour eating window, you consume your calculated daily calorie needs. For example, if your adjusted calorie intake is 1,800 kcal, spread this across your meals during the eating period.

Monitor and Adjust

Track your progress and adjust your calorie intake as needed. Factors like changes in weight, activity level, or goals may require recalculating your needs.

Using tools like online calorie calculators and food tracking apps can help simplify this process.

How to determine your daily caloric needs

To determine your daily caloric needs, follow these essential steps:

Calculate Your Basal Metabolic Rate (BMR)

The BMR is the number of calories your body needs to perform basic life-sustaining functions, like breathing and digestion, while at rest. You can calculate your BMR using the Mifflin-St Jeor formula, which varies based on your sex:

• For Men:

$$ BMR = 10 \times \text{weight (kg)} + 6.25 \times \text{height (cm)} - 5 \times \text{age (years)} + 5 $$

• For Women:

$$ BMR = 10 \times \text{weight (kg)} + 6.25 \times \text{height (cm)} - 5 \times \text{age (years)} - 161 $$

This gives you a base number of calories your body needs to function at rest.

Determine Your Total Daily Energy Expenditure (TDEE)

To get a more accurate daily caloric need, consider your activity level. Multiply your BMR by a factor that reflects your daily activity:

Multiply your BMR by the appropriate activity factor to determine your TDEE. This number represents the total calories you need to maintain your current weight.

Adjust for Weight Goals

• To Lose Weight: Subtract 500–1,000 calories per day from your TDEE for a safe weight loss of 0.5–1 kg per week.

• To Gain Weight: Add 500–1,000 calories per day to your TDEE to gain weight at a similar rate.

Regular Monitoring and Adjustments

Your caloric needs might change based on age, weight fluctuations, or changes in your activity level. Regularly reassess and adjust your intake as needed.

What can be consumed during fasting?

When engaging in intermittent fasting, it is crucial to maintain a state that encourages fat burning and metabolic benefits.

The following table outlines what can be consumed during fasting to stay in the fasted state without breaking it:

Additional Considerations:

• Bone Broth: Although nutritious, bone broth contains calories and protein. Consuming it will break a strict fast but may be suitable for less stringent fasting methods, such as during a prolonged fast where a small caloric intake is allowed.

• Diet Sodas: While technically calorie-free and allowed, diet sodas might not be the best choice as artificial sweeteners can affect gut health and potentially trigger cravings.

During fasting, the primary goal is to avoid anything that could cause an insulin response or disrupt the metabolic state. Therefore, it’s best to stick to non-caloric, simple beverages and supplements that do not contain any hidden calories or sugars.

How many meals can we eat during the day?

The number of meals you should eat during the day while practising intermittent fasting largely depends on the specific fasting regimen you’re following. However, generally speaking, most people stick to two or three meals within their eating window. The key is to ensure these meals are balanced and provide the necessary nutrients to fuel your body.

When deciding how many meals to eat, listen to your body’s hunger cues and ensure you’re getting enough calories to support your energy levels. The goal is to strike a balance between the benefits of fasting and maintaining proper nutrition.

Conclusion

To master intermittent fasting, calorie calculation is key.

Begin by determining your Basal Metabolic Rate (BMR) to understand your basic energy needs. Then, adjust for your activity level to get your Total Daily Energy Expenditure (TDEE).

This becomes your guide for how many calories to consume during eating windows. For weight loss, aim for a moderate calorie deficit—around 10-20% below your TDEE.

Remember, extreme cuts can backfire, leading to fatigue and muscle loss. Keep track of your progress and be ready to tweak your intake based on how your body responds.

Intermittent fasting isn’t just about when you eat, but how well you nourish your body within those periods.