How Body Recomposition Calories Are Calculated

요약

Body recomposition is the process of building muscle and losing fat simultaneously, rather than going through separate bulk and cut phases. The key nutritional strategy is calorie cycling — eating slightly more on training days to fuel muscle growth and less on rest days to promote fat loss. This calculator estimates your daily calorie and macro targets for each day type, based on your body composition, training experience, and goals.

작동 방식

The calculator follows a four-step process:

1. Estimate your BMR using the Mifflin-St Jeor equation (the most accurate predictive equation for resting energy expenditure)
2. Calculate your TDEE by multiplying BMR by an activity factor
3. Apply calorie cycling — adjust TDEE up or down depending on whether it’s a training day or rest day, and which goal you’ve selected
4. Calculate macros — protein is set per kg bodyweight (higher in a deficit), fat as a percentage of daily calories, and carbs fill the remaining calories

Why calorie cycling?

The rationale is straightforward: on training days, a slight surplus provides energy for resistance training and supports muscle protein synthesis in the hours after exercise. On rest days, a deficit taps into fat stores. Over the week, the net effect is a mild deficit or near-maintenance intake — enough to lose fat slowly while building muscle.

The evidence for a physiological advantage of cycling over constant intake is modest (Barakat et al., 2020). The primary benefit may be psychological: eating more on training days improves adherence and workout quality.

The formulas

Step 1: BMR (Mifflin-St Jeor)

This is the simplified form from Mifflin et al. (1990). The original paper used coefficients 9.99, 6.25, and 4.92, but the authors noted that rounding to 10, 6.25, and 5 “did not affect its predictive value.”

Step 2: TDEE

TDEE = BMR × activity multiplier:

Step 3: Calorie cycling

Daily calories are adjusted relative to TDEE based on the selected goal:

The fat-loss rest day deficit of −25% is deliberately aggressive — it is appropriate for users who are prioritising fat loss and are comfortable with a larger rest-day deficit. Users who find this too restrictive should select the balanced goal.

Step 4: Macros

Protein is set per kg bodyweight, varying by goal:

Fat is a fixed percentage of daily calories:

Carbs fill the remaining calories after protein and fat: carbsG = (calories − proteinG × 4 − fatG × 9) / 4

Expected muscle gain rates

Based on Lyle McDonald’s training experience model:

These are upper-end estimates for natural trainees with good genetics, training, and nutrition. Individual results vary significantly.

계산 예시

입력값 설명

• Weight / Height / Age / Sex — used to calculate BMR via Mifflin-St Jeor
• Activity level — overall daily activity including non-exercise movement, used to estimate TDEE
• Body fat % — used to calculate current lean mass and fat mass, and to determine recomp difficulty
• Training days per week — how many days you do resistance training; affects the weekly calorie average
• Training experience — beginner, intermediate, or advanced; determines expected muscle gain rate and fat loss rate
• Recomp goal — fat loss, balanced, or muscle gain priority; determines calorie cycling multipliers and protein targets

출력값 설명

• Training day calories + macros — what to eat on days you lift weights
• Rest day calories + macros — what to eat on non-training days
• BMR — your basal metabolic rate (calories burned at rest)
• Weekly calorie balance — total weekly surplus or deficit relative to TDEE
• Est. muscle gain — expected monthly muscle gain based on experience level (Lyle McDonald model)
• Est. fat loss — expected monthly fat loss based on current fat mass and experience
• Body composition bar — visual breakdown of current lean mass vs fat mass
• 12-week projection — estimated body fat % trajectory over 12 weeks
• Difficulty rating — how realistic recomposition is given your body fat % and training experience (easy → very hard)

가정 및 제한사항

• BMR equations are estimates. Mifflin-St Jeor is the most validated equation for healthy adults, but individual metabolic rate can vary by 10–15% due to genetics, thyroid function, and other factors.
• Activity multipliers are broad categories. Real TDEE depends on NEAT (non-exercise activity thermogenesis), which varies hugely between individuals.
• Calorie cycling is one approach, not the only one. Constant daily intake at a mild deficit can also achieve recomposition (Barakat et al., 2020).
• Muscle gain projections are optimistic. The Lyle McDonald model assumes optimal training, nutrition, recovery, and genetics. Most people will gain somewhat less.
• Body fat % is self-reported. Accuracy depends on the measurement method (DEXA, calipers, visual estimate). Small errors in BF% significantly affect lean/fat mass calculations.
• Not suitable for clinical use. These are general guidelines for healthy adults doing resistance training. People with medical conditions, eating disorders, or extreme body compositions should consult a healthcare professional.
• Recomp is slow. Visible results typically take 8–16 weeks. Scale weight may not change even as body composition improves. Progress is best tracked with measurements, photos, and strength gains.

검증

All values verified by hand calculation against Mifflin-St Jeor formula and calorie cycling multipliers.