Method & sources

Medical disclaimer

Jyva does not provide medical, dietary or professional healthcare advice, and is not a substitute for a consultation with a doctor or a registered dietitian — especially if you have a medical condition, are pregnant, or are about to start intensive training. Check with a doctor before making decisions about your health. See also: Terms of use.

1. Basal metabolic rate (BMR)

Calculated with the Mifflin-St Jeor equation from your height, weight, age and sex — the most accurate of the usual predictive equations in the general population. It estimates what your body burns at complete rest.

Sources :

• Basal metabolic rate using indirect calorimetry — accuracy of predictive equations (PubMed, 2024)
• Validity of predictive equations to estimate RMR in females with varying BMI (PMC)

2. Total daily energy expenditure (TDEE)

Your basal rate multiplied by an activity factor, from 1.2 (sedentary) to 1.725 (6 or more sessions a week), derived from your training frequency. It is an estimate, not a measurement.

Source : Accuracy of four resting metabolic rate prediction equations (ScienceDirect)

3. Calorie deficit or surplus

Derived from the weekly pace you chose, on the basis of about 7,700 kcal per kilogram of body fat. Usual recommendations put a sustainable deficit at 15–25% of total expenditure.

Sources :

• Calorie deficit explained — Harvard Health Publishing
• Nutrition recommendations for bodybuilders in the off-season (Iraki et al., 2019 — PubMed)

4. Safety limits

Your target never falls below 1,200 kcal for women or 1,500 kcal for men, the usual clinical thresholds, and never exceeds your expenditure by more than 40% — beyond that, a surplus adds fat without extra muscle.

Source : Evidence-based recommendations for natural bodybuilding contest preparation (PubMed)

5. Protein

2 g per kilogram of body weight, at the top of the 1.6–2.2 g/kg range that the literature associates with muscle gain in people who train.

Sources :

• ISSN Position Stand: protein and exercise (Jäger et al., 2017 — PMC)
• Systematic review and meta-analysis of protein supplementation (Morton et al., 2018 — PubMed)
• Protein Science Updated (Stronger by Science)

6. Fat

1 g per kilogram of body weight, above the minimum usually recommended to preserve hormonal function.

Sources :

• Fat Requirements For Optimal Hormonal Health
• Nutritional Recommendations for Physique Athletes (PMC)

7. Carbohydrates

What remains of your calorie target once protein and fat are covered — the usual approach in strength training, where carbohydrates fuel performance.

Source : ISSN Position Stand: nutrient timing (PMC)

8. Hydration

A base of 8 to 10 glasses of 200 ml depending on your sex and weight, calibrated on the 2.0 L and 2.5 L of total water intake referenced by EFSA — of which roughly 20–30% already comes from food. A bonus is added on training days.

Source : Scientific Opinion on Dietary Reference Values for water — EFSA Journal 2010; 8(3):1459

9. Calories burned

Read from Apple Health when you allow it. Otherwise estimated from the MET value of strength training (4.5), your weight and the duration of the session.

Source : 2011 Compendium of Physical Activities: a second update of codes and MET values (Ainsworth et al. — PubMed)

10. Meal scan

Calories, macros and health score are estimated by an AI model (GPT-4o) from your photo. They are estimates, not certified measurements — you can correct every value in the app.

Source : Customized multimodal Diabot-GPT-4o enhances accuracy of image-based dietary assessments: validation against weighed food records (Chen et al., 2025 — Am J Clin Nutr, PubMed)

11. Weight projection

A linear extrapolation of the pace you chose, shown to make the goal tangible. It is not a prediction: actual progress varies from one person to another.

Sources :

• Caloric equivalents of gained or lost weight (Wishnofsky, 1958 — Am J Clin Nutr, PubMed)
• Can a weight loss of one pound a week be achieved with a 3500-kcal deficit? (Thomas et al., 2013 — PubMed)
• Quantification of the effect of energy imbalance on bodyweight (Hall et al., 2011 — The Lancet, PubMed)

12. Cycle tracking

If you enable it, the suggested intensity is adjusted by a simple date-window heuristic computed on your device. It is neither a hormonal model nor medical advice.

Source : The Effects of Menstrual Cycle Phase on Exercise Performance in Eumenorrheic Women: A Systematic Review and Meta-Analysis (McNulty et al., 2020 — Sports Med, PubMed)

13. Estimated 1RM

Your one-rep max is estimated from your best set with the Epley formula: weight × (1 + reps ÷ 30). It is an estimate, not a tested max — never attempt a true max without a proper warm-up and a spotter.

Source : The Accuracy of Prediction Equations for Estimating 1-RM Performance in the Bench Press, Squat, and Deadlift (LeSuer et al., 1997 — J Strength Cond Res)