Articles / Nutrition fundamentals
Nutrition fundamentals
Calories, TDEE, protein, fat, carbs — the numbers and where they come from.
What is TDEE?
TDEE is the total energy you spend in a day: resting metabolism plus digestion plus movement. What it is made of, how a calculator estimates it, and how far off it can be.
Reference valuesNutrition fundamentals4 minBMR vs TDEE: what's the difference?
BMR is what your body spends at complete rest; TDEE adds digestion and movement on top. The exact multiplier table our calculator uses, and which number the target is built from.
First principlesNutrition fundamentals4 minHow to calculate your TDEE by hand
Three steps to your TDEE with a pen: the Mifflin-St Jeor equation, the exact activity multiplier our calculator uses, and a two-week check against real intake and weight data.
First principlesNutrition fundamentals5 minMifflin-St Jeor vs Harris-Benedict vs Katch-McArdle: which BMR formula is best?
The four common BMR equations side by side — what each needs as input, how far off they typically are for an individual, and why our calculator uses Mifflin-St Jeor.
Human trial dataNutrition fundamentals5 minWhy does every TDEE calculator give a different number?
Different BMR equations, different activity multipliers and different rounding add up to gaps of several hundred kcal between calculators. Where each gap comes from and what to do with the number.
First principlesNutrition fundamentals5 minWhat is NEAT and why does it matter for calories?
NEAT is the energy you spend on everything that is not sleeping, eating or training. Why it is the most variable part of your day, how our multiplier adjusts for it, and why it drops when you diet.
Reference valuesNutrition fundamentals5 minWhich activity level should I pick on a calorie calculator?
The five activity levels on our calorie calculator, the exact multiplier behind each, how training days and job activity combine, and what to do if you sit between two levels.
First principlesNutrition fundamentals6 minHow do apps estimate your energy expenditure from your logs?
Adaptive apps back-calculate expenditure from what you logged and how trend weight moved. Why it takes about three weeks, what a half-logged day does to it, and the 3-of-7 rule MacroDiet uses.
First principlesNutrition fundamentals6 minIs calories in, calories out true?
Calories in, calories out is true as bookkeeping and misleading as a plan: the "out" side moves when you diet. What adapts, why 7,700 kcal per kg is a planning number, and what it means for tracking.
First principlesNutrition fundamentals6 minWhy doesn't exercise burn as many calories as my tracker says?
Two reasons: wrist trackers overstate exercise energy by 20% or more, and the body compensates so a 400 kcal session adds less than 400 kcal to the day. Why we never add exercise calories back.
Human trial dataNutrition fundamentals5 minWhat is the thermic effect of food?
The thermic effect of food is the energy spent digesting and storing a meal — roughly a tenth of what you eat. How it differs by macronutrient and why it is already inside your TDEE estimate.
Reference valuesNutrition fundamentals8 minHow many calories should I eat a day?
A calorie target starts from TDEE and moves by a rate of body weight per week, capped at 35% and held above a floor. The exact rules our calculator applies, with three worked examples.
First principlesNutrition fundamentals5 minWhat are macros?
Macros are the three nutrients that carry calories: protein, fat and carbohydrate. What each is, the calories per gram, and how a macro target is set.
Reference valuesNutrition fundamentals5 minHow much protein per kg of body weight?
From the 0.8 g/kg RDA to the 1.2–2.4 g/kg tiers MacroDiet uses, why the target rises 0.2 g/kg on a deficit, and when protein gets capped at 50% of calories.
Human trial dataNutrition fundamentals4 minWhat is the minimum fat intake per day?
MacroDiet never sets fat below max(0.6 g/kg, 20% of calories). Why fat has a floor, the two ways to compute it, and what happens to the split at low calories.
Reference valuesNutrition fundamentals5 minHow many carbs should I eat per day?
Carbs are what is left after protein and fat: the formula, the 45–65% reference range, typical g/kg ranges by activity, and where low-carb and keto thresholds sit.
Reference valuesNutrition fundamentals4 minHow much fiber per day?
The adult reference values are 38 g (men) and 25 g (women), derived from 14 g per 1,000 kcal. Why the rate scales with intake, and how fibre sits inside your carb count.
Reference valuesNutrition fundamentals4 minWhy don't my macros add up to my calories?
Protein × 4 + carbs × 4 + fat × 9 rarely equals the label. Specific energy factors, fibre, sugar alcohols, alcohol and rounding explain the gap — and which number to log.
First principlesNutrition fundamentals4 minWhat is IIFYM (If It Fits Your Macros)?
IIFYM means hitting daily protein, fat and carb targets with any foods that fit. What the idea says, what it does not, where fibre fits, and how a weekly budget changes it.
First principlesNutrition fundamentals5 minMacro diet for beginners: how to start counting macros
Get three numbers, weigh food for two weeks, hit protein first, accept 80/20 accuracy, and adjust only after real data. A method guide, not a meal plan.
Method / guideNutrition fundamentals5 minHow are keto macros calculated?
On keto MacroDiet fixes carbs at 30 g, sets protein from body weight, and gives fat every remaining calorie. The ceiling, the flipped order, and a worked example.
First principlesNutrition fundamentals5 minBalanced, low-fat, low-carb or keto: which macro split for fat loss?
The four MacroDiet styles side by side at 2,000 kcal: protein identical, fat 20–50% of the remainder or the keto ceiling. How to choose by adherence, with a worked example.
First principlesNutrition fundamentals4 minHow many calories are in alcohol, and how do you log it?
Alcohol carries 7 kcal per gram; a US standard drink holds 14 g, about 98 kcal before mixers. How to work out any drink and how to log it as carbs or fat.
Reference valuesNutrition fundamentals5 minHow do you set macros on a vegan diet?
Protein tiers do not change on a plant-based diet; the foods that reach them do. The targets, the nutrients worth watching, and why the fat/carb split tends to shift.
Reference valuesNutrition fundamentals4 minHow much water should you drink a day?
The reference values are 3.7 L (men) and 2.7 L (women) of total water a day, and total means food and all drinks. What counts, how much food supplies, and why training changes it.
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Zyra is a training and nutrition tracking tool. Nothing on this page is medical advice, a diagnosis, or an individual prescription. The numbers are estimates from published formulas and the apps' own rules — consult a qualified professional for decisions about your health, and a coach for your training.