How Protein Intake Is Calculated

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Protein is one of the three macronutrients and plays a central role in building and repairing muscle tissue, producing enzymes and hormones, and supporting immune function. How much you need each day depends on your body weight, your fitness goal, and your age.

The UK Reference Nutrient Intake (RNI) is 0.75 g/kg/day — enough to prevent deficiency in sedentary adults. But if you exercise, are trying to lose fat without losing muscle, or are over 50, the evidence points to substantially higher intakes. This calculator uses goal-specific ranges drawn from sports science meta-analyses and clinical guidelines.

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The calculator multiplies your body weight (in kg) by a per-kilogram multiplier that depends on your goal and age group. Each multiplier pair (low and high) defines a recommended range rather than a single target, because individual needs vary with training intensity, calorie intake, and body composition.

Four goals are supported:

1. General health — the minimum (NHS RNI) to a moderately active upper bound (BDA)
2. Muscle building — the range supported by the Morton et al. (2018) meta-analysis
3. Fat loss / recomposition — elevated protein to preserve muscle during energy restriction (Helms et al., 2014)
4. Endurance sport — the range for aerobic athletes (BDA, ISSN)

For adults over 50, the lower bounds are raised to reflect ESPEN and PROT-AGE guidelines on age-related anabolic resistance.

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Multipliers by goal and age

The “target” shown in the calculator is the midpoint of the low–high range.

Derived values

• Per-meal protein = daily total ÷ 4 meals (Schoenfeld & Aragon, 2018 recommend distributing protein evenly across 4+ meals for optimal muscle protein synthesis)
• Calories from protein = daily grams × 4 kcal/g (the Atwater factor for protein)

Worked examples

75 kg adult, muscle building, under 50

65 kg adult, general health, over 50

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• Body weight — in kilograms (or pounds in imperial mode, converted internally). Protein needs scale linearly with body weight.
• Goal — determines which evidence-based multiplier range is used. “Fat loss” uses the highest multipliers because preserving muscle in a caloric deficit requires more protein.
• Age group — adults over 50 have higher minimum requirements due to age-related anabolic resistance (the body becomes less efficient at using dietary protein to build muscle).
• Units — toggle between metric (kg) and imperial (lbs). The conversion uses 1 lb = 0.453592 kg.

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• Daily protein target — the recommended range in grams per day, shown as low–high with a midpoint.
• Low / Target / High — the three breakpoints of the range. “Target” is the arithmetic mean of low and high.
• Per meal — daily target divided by 4 meals, based on evidence that distributing protein across 4+ eating occasions optimises muscle protein synthesis.
• Calories from protein — total grams multiplied by 4 kcal/g (the standard Atwater energy factor for protein).
• Food examples — how many portions of common protein-rich foods would meet the daily target, to help users visualise real meals.

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• Body weight, not lean mass — the multipliers use total body weight. For individuals with very high body fat, protein per kg of lean body mass may be more appropriate (e.g., Helms et al. report 2.3–3.1 g/kg FFM for lean athletes in a deficit). This calculator does not adjust for body composition.
• Ranges, not prescriptions — the calculator shows evidence-based ranges, not individualised medical advice. Actual needs vary with training volume, calorie intake, injury status, and health conditions.
• 4-meal assumption — per-meal targets assume even distribution across 4 meals. Fewer or more meals will change the per-meal number but not the daily total.
• No upper safety limit modelled — very high protein intakes (>2.5 g/kg) are generally safe in healthy adults but may be contraindicated for people with kidney disease. The calculator does not screen for medical conditions.
• “Over 50” is a simplification — ESPEN and PROT-AGE guidelines target adults 65+. The calculator uses 50 as the threshold to be conservative, since some age-related muscle loss begins in the 40s–50s.

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