Metabolism & Nutrition Scientific Catalog

Sports Nutrition Calculators: The Complete Science-Backed Reference

Nutrition is responsible for 60–80% of body composition outcomes and is the primary performance lever most athletes underutilise. No training programme survives a chronic caloric mismatch or an inadequate protein distribution. The calculators in this cluster translate peer-reviewed sports nutrition science into actionable numbers.

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The Foundation: Energy Balance and TDEE

Every nutrition decision originates from Total Daily Energy Expenditure (TDEE) — the total number of calories your body burns in 24 hours. TDEE is not a fixed number; it adjusts over time in response to changes in body weight, training load, and adaptive thermogenesis.

The Mifflin-St Jeor equation (1990) is the current clinical standard for estimating Basal Metabolic Rate (BMR), outperforming the older Harris-Benedict formula in validation studies with ±10% accuracy in non-obese adults. For athletes with known lean body mass, the Katch-McArdle formula removes the body weight variable and predicts BMR from fat-free mass, improving accuracy to ±5%.

Activity multipliers (PAL factors from the FAO/WHO/UNU framework) convert BMR to TDEE. The standard sedentary multiplier (1.2) is frequently misapplied — most desk workers who exercise 3–4× per week are better classified at 1.55 (moderately active), and competitive athletes training 10+ hours per week should use 1.725–1.9.

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Macronutrient Allocation: The Evidence-Based Splits

The three macronutrients have distinct roles in athletic performance:

Protein is the structural macronutrient. Morton et al. (2018) conducted a meta-analysis of 49 RCTs (n=1,800) and found that 1.62 g/kg/day is the point at which protein supplementation plateaus for muscle protein synthesis in resistance-trained individuals. A practical upper bound of 2.2 g/kg/day is recommended for athletes in caloric deficit to maximise lean mass preservation (Helms et al., 2014).

Carbohydrates are the primary fuel for high-intensity work. At intensities above 70% VO₂ max, carbohydrate oxidation is the dominant energy pathway. Carbohydrate periodisation — high-carb on training days, reduced on rest days — is used at the elite level to optimise body composition without compromising performance capacity.

Dietary fat supports hormonal function, fat-soluble vitamin absorption, and serves as the primary fuel for sub-threshold aerobic work. The minimum recommended fat intake for hormonal health is 0.5–1.0 g/kg/day; falling below this threshold consistently suppresses testosterone in males and disrupts menstrual function in females.

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Specialised Diets: Keto, Paleo, and Intermittent Fasting

Ketogenic diets shift primary fuel utilisation from glucose to ketone bodies derived from dietary fat. At a standard keto split of 75% fat / 20% protein / 5% carbohydrate, blood ketones reach 0.5–3.0 mmol/L within 3–5 days of strict adherence. Keto is most supported for fat loss in sedentary individuals and endurance athletes who have fully keto-adapted (8–12 weeks). It is not recommended for athletes performing high-intensity intervals, sprint work, or heavy compound lifting — carbohydrates are mechanistically required for glycolytic ATP production.

Intermittent fasting protocols (16:8, 5:2, OMAD) produce caloric restriction through time restriction rather than food category restriction. A 2020 review in *Obesity Reviews* found that IF and continuous caloric restriction produce equivalent fat loss outcomes over 12–52 weeks, suggesting that IF's benefits are primarily from reducing total caloric intake rather than any metabolic mechanism unique to fasting. Athletic performance is not impaired if the eating window encompasses the training window.

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Supplements: Ranked by Evidence

The International Society of Sports Nutrition (ISSN) evidence-based supplement ranking places only four substances in the highest-evidence Tier 1 category:

1. Creatine monohydrate — The most researched ergogenic supplement with 500+ peer-reviewed studies. A loading phase (20g/day × 5 days) reaches muscle saturation 20× faster than maintenance dosing (3–5g/day), but both reach equivalent levels at week 4.

2. Caffeine — 3–6 mg/kg pre-workout increases time-to-exhaustion by 12–15% through adenosine receptor antagonism. Half-life of 5–6 hours means afternoon consumption disrupts sleep architecture in caffeine-sensitive individuals.

3. Beta-alanine — Increases carnosine buffering capacity for efforts of 1–4 minutes. Paresthesia (tingling) at doses >800mg can be avoided by splitting into 400mg doses.

4. Protein supplementation — Effective only when total daily protein falls below the 1.6 g/kg threshold. Whole food protein and supplement protein are physiologically equivalent.

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Practical Application: Using These Calculators Together

The optimal sequence for nutrition planning:

1. Calculate TDEE to establish your energy baseline

2. Set a caloric target (deficit for fat loss: 300–500 kcal/day; surplus for muscle gain: 150–250 kcal/day)

3. Calculate macro splits from your TDEE and goal

4. Use the Meal Planner to distribute macros across meals

5. Add targeted supplements using the Creatine and Caffeine calculators