Health Calculations – GRND

Last updated: March 14, 2026

This page documents the scientific methodology behind GRND's diet planning calculations, including BMR, TDEE, target calories, macronutrient distribution, and time-to-goal estimation.

1. Basal Metabolic Rate (BMR)

BMR is calculated using the Mifflin-St Jeor Equation, the most validated equation for estimating resting energy expenditure in the general population.

Male: BMR = (10 × weight_kg) + (6.25 × height_cm) − (5 × age) + 5
Female: BMR = (10 × weight_kg) + (6.25 × height_cm) − (5 × age) − 161

Source: Mifflin MD et al. (1990). A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. PMID: 2305711

2. Total Daily Energy Expenditure (TDEE)

TDEE is calculated by multiplying BMR by an activity multiplier that reflects the user's daily physical activity level.

TDEE = BMR × Activity Multiplier

Activity Level	Description	Multiplier
Sedentary	Little or no exercise	1.2
Light	Light exercise 1–3 days/week	1.375
Moderate	Moderate exercise 3–5 days/week	1.55
Active	Hard exercise 6–7 days/week	1.725
Very Active	Very hard exercise or physical job	1.9

Source: Harris JA, Benedict FG (1918). A biometric study of human basal metabolism. Proc Natl Acad Sci USA.

3. Target Calories

Daily calorie targets are adjusted from TDEE based on the user's selected goal:

Lose weight:   Target = TDEE − Calorie Deficit
Gain weight:   Target = TDEE + Calorie Surplus
Maintain:      Target = TDEE

The maximum allowable calorie deficit is capped at 80% of TDEE to prevent unsafe caloric restriction.

4. Macronutrient Distribution

Macronutrients are allocated as a percentage of total target calories, adjusted per goal. Protein and carbohydrates provide 4 kcal/g; fat provides 9 kcal/g.

Goal	Protein	Carbohydrates	Fat
Lose weight	40%	35%	25%
Gain weight	30%	50%	20%
Maintain	30%	45%	25%

5. Time-to-Goal Estimation

Weight Loss — Two-Phase Model

Weight loss rate changes over time due to metabolic adaptation. GRND uses a two-phase model:

First 12 weeks: 4,400 kcal per kg lost
After 12 weeks: 6,000 kcal per kg lost

The higher energy cost after 12 weeks reflects the body's metabolic adaptation — as weight decreases and the body adjusts, the same calorie deficit produces slower results.

First 12 weeks: Garrow JS, Summerbell CD (1995). Meta-analysis: effect of exercise on weight loss in overweight subjects. Eur J Clin Nutr. PMID: 3235270

After 12 weeks (metabolic adaptation): Leibel RL et al. (1995). Changes in energy expenditure resulting from altered body weight. N Engl J Med. PMID: 22257646

Weight Gain — Energy Cost Model

Weight gain energy cost is estimated at ~6,800 kcal per kg, derived from a realistic body composition gain model:

Assuming 1 kg of scale weight gain is composed of ~0.3 kg lean mass and ~0.7 kg fat:

0.3 kg × 5,000 kcal/kg (muscle energy density) = 1,500 kcal
0.7 kg × 7,700 kcal/kg (fat energy density) = 5,390 kcal
Total ≈ 6,800 kcal/kg gained

Fat energy density: Hall KD (2008). What is the required energy deficit per unit weight loss? Int J Obes. PMID: 17848938

Muscle/FFM energy density (~5,000 kcal/kg): Hall KD (2007). Body fat and fat-free mass inter-relationships. Br J Nutr. PMID: 17367567

Disclaimer: All calculations provided by GRND are estimates based on population-level research and are intended for general fitness guidance only. They are not a substitute for professional medical or dietary advice. Individual results may vary. Consult a qualified healthcare provider before making significant changes to your diet or exercise routine.