Last reviewed August 2026

Scientific Sources

The published research and public health guidelines behind every calculation Gravl Macros makes.

1. About These Sources

Gravl Macros estimates your energy expenditure, calorie targets, macronutrients and micronutrient goals using published formulas and public health guidelines. This page lists each recommendation the app makes and the sources it is based on.

All of the app's numbers are estimates, not medical advice. Individual needs vary. Read our Health Disclaimer and consult a qualified healthcare professional before making changes to your diet, especially if you have a medical condition, are pregnant or breastfeeding, or have a history of disordered eating.

2. Energy Expenditure

2.1. Basal Metabolic Rate

The app estimates your basal metabolic rate with the Katch-McArdle equation, which derives resting energy expenditure from lean body mass (body weight minus estimated body fat). Lean-mass-based equations account for differences in body composition that weight-and-height formulas miss.

  • Cunningham JJ (1980). A reanalysis of the factors influencing basal metabolic rate in normal adults. The American Journal of Clinical Nutrition, 33(11), 2372–2374. pubmed.ncbi.nlm.nih.gov/7435433
  • McArdle WD, Katch FI, Katch VL. Exercise Physiology: Nutrition, Energy, and Human Performance. Wolters Kluwer. The lean-mass equation popularized in this textbook (370 + 21.6 × lean body mass in kg) is the one the app uses.

2.2. Activity and Daily Movement

Daily energy expenditure is estimated by multiplying basal metabolic rate by a physical activity factor between 1.2 and 1.9, built from your non-exercise daily movement (or your average step count when available) plus additions for exercise frequency and cardio. This range follows the physical activity levels defined by the FAO/WHO/UNU expert consultation on human energy requirements, and the treatment of non-exercise movement follows research on non-exercise activity thermogenesis (NEAT).

  • FAO/WHO/UNU (2004). Human Energy Requirements. Report of a Joint FAO/WHO/UNU Expert Consultation. fao.org/4/y5686e/y5686e00.htm
  • Levine JA (2002). Non-exercise activity thermogenesis (NEAT). Best Practice & Research Clinical Endocrinology & Metabolism, 16(4), 679–702. pubmed.ncbi.nlm.nih.gov/12468415
  • Tudor-Locke C, Bassett DR (2004). How many steps/day are enough? Preliminary pedometer indices for public health. Sports Medicine, 34(1), 1–8. pubmed.ncbi.nlm.nih.gov/14715035

2.3. Thermic Effect of Food

The app accounts for the energy your body spends digesting food, using 25% of protein calories, 8% of carbohydrate calories and 3% of fat calories — within the ranges reported in the research literature (protein 20–30%, carbohydrate 5–10%, fat 0–3%).

2.4. Adaptive Expenditure

After onboarding, the app continuously refines your expenditure estimate from your logged food intake and smoothed weight trend, based on the principle that changes in body weight over time reflect the balance between energy intake and energy expenditure.

3. Calorie Targets and Rate of Change

3.1. Energy Density of Weight Change

To convert your chosen weekly weight-change pace into a daily calorie adjustment, the app uses the conventional value of ~7,700 kcal per kilogram of body weight change.

3.2. Safe Rates and Deficit Limits

The app caps calorie deficits at 25% of your total expenditure and surpluses at 20%, and limits the selectable pace to at most 1.0 kg per week. Gradual weight loss — commonly 0.25–1.0 kg (about 0.5–2 lb) per week — is associated with better retention of lean mass and performance than aggressive deficits.

3.3. Minimum Calorie Floors

Regardless of goal, the app will not set targets below 1,500 kcal/day for men and 1,200 kcal/day for women by default, consistent with the low-calorie diet ranges used in clinical obesity treatment guidelines. An optional lower floor (1,200/1,000 kcal) can be enabled explicitly and the app warns to monitor energy levels closely; intakes at or below these levels are best undertaken with professional supervision.

  • National Heart, Lung, and Blood Institute / NIH (1998). Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults. ncbi.nlm.nih.gov/books/NBK2003

3.4. Metabolic Adaptation and Refeeds

During prolonged deficits the app models a gradual reduction in expenditure (up to 15%) to reflect adaptive thermogenesis, and offers optional refeed days at roughly maintenance intake based on research into intermittent energy restriction.

  • Rosenbaum M, Leibel RL (2010). Adaptive thermogenesis in humans. International Journal of Obesity, 34(S1), S47–S55. pubmed.ncbi.nlm.nih.gov/20935667
  • Trexler ET, Smith-Ryan AE, Norton LE (2014). Metabolic adaptation to weight loss: implications for the athlete. Journal of the International Society of Sports Nutrition, 11, 7. pubmed.ncbi.nlm.nih.gov/24571926
  • Byrne NM, et al. (2018). Intermittent energy restriction improves weight loss efficiency in obese men: the MATADOR study. International Journal of Obesity, 42(2), 129–138. pubmed.ncbi.nlm.nih.gov/28925405

4. Protein

Protein targets range from 1.3 to 2.4 g per kg of lean body mass depending on the preference you choose, with small additions when dieting, when highly active, and from age 40 onward — and never below the Recommended Dietary Allowance of 0.8 g per kg of body weight. These ranges are consistent with the protein intakes supported by meta-analyses and position stands for people doing resistance or endurance training, with lean-mass-based targets drawn from evidence-based contest-preparation recommendations, and the age adjustment from expert recommendations for older adults.

5. Fat, Carbohydrate and Fiber

After protein is set, remaining calories are split between fat and carbohydrate according to your chosen diet style, with fat never set below 20% of calories — the lower bound of the Acceptable Macronutrient Distribution Range. The app warns when a configuration takes carbohydrate below 50 g/day (well under the 130 g/day RDA). The fiber target is 14 g per 1,000 kcal, per the Dietary Guidelines for Americans.

6. Hydration

The water goal starts at 33 ml per kg of body weight and scales up to 1.4× with activity — in line with the adequate intakes for total water established by the European Food Safety Authority (2.0 L/day for adult women, 2.5 L/day for adult men, more with physical activity and heat).

7. Micronutrients

Micronutrient goals (fiber, sugars, sodium, saturated and trans fat, cholesterol, potassium, calcium, iron, vitamins A, C and D, magnesium, phosphorus and zinc) follow the Dietary Reference Intakes published by the National Academies and NIH — the practical floor corresponds to the Estimated Average Requirement, the target to the RDA or Adequate Intake for your sex and age, and the ceiling to the Tolerable Upper Intake Level — complemented by WHO guidelines for sodium, free sugars and trans fat, the NHS reference intake for total sugars, and the American Heart Association / earlier Dietary Guidelines figure for cholesterol.

If you spot an error on this page or want to suggest an additional source, contact us at support@gravl.ai.