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: rest, digestion and 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 multiplier table we use, and which number the target is built from.
First principlesNutrition fundamentals4 minHow to calculate your TDEE by hand
Three steps to your TDEE by hand: the Mifflin-St Jeor equation, the exact activity multiplier our calculator uses, and a two-week check against your real 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 one person, and why we use Mifflin-St Jeor.
Human trial dataNutrition fundamentals5 minWhy does every TDEE calculator give a different number?
Different BMR equations, multipliers and rounding add up to gaps of several hundred kcal between calculators. Where each gap comes from and what to do next.
First principlesNutrition fundamentals5 minWhat is NEAT and why does it matter for calories?
NEAT is the energy spent on everything but sleep, food and training. Why it varies so much, how our multiplier adjusts for it, and why it drops on a 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 and job activity combine, and what to do between two levels.
First principlesNutrition fundamentals6 minHow do apps estimate your energy expenditure from your logs?
Adaptive apps back-calculate expenditure from logged intake and trend weight. Why it takes about three weeks, what half-logged days do, and the 3-of-7 rule.
First principlesNutrition fundamentals6 minIs calories in, calories out true?
Calories in, calories out is true as bookkeeping but not as a plan: the out side moves as you diet. What adapts, and why 7,700 kcal per kg is a planning number.
First principlesNutrition fundamentals10 minWhy doesn't exercise burn as many calories as my tracker says?
Wrist trackers miss exercise calories by 20% or more, and the body compensates, so a 400 kcal session adds less. 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 a meal — about a tenth of intake. How it differs by macro and why your TDEE already includes it.
Reference valuesNutrition fundamentals8 minHow many calories should I eat a day?
A calorie target starts from TDEE and moves by a weekly rate of body weight, capped at 35% and held above a floor. The exact rules, 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 fundamentals9 minHow much protein per kg of body weight?
The RDA is 0.8 g/kg, but in 49 trials lean-mass gains levelled off near 1.6 g/kg a day. The 1.2–2.4 g/kg tiers Zyra Nutrition uses, the deficit bump, the cap.
Human trial dataNutrition fundamentals4 minWhat is the minimum fat intake per day?
Zyra Nutrition 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, g/kg ranges by activity, and where the 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), from 14 g per 1,000 kcal. Why the rate scales with intake, and how fibre sits in 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 and rounding explain the gap — and what to log.
First principlesNutrition fundamentals4 minWhat is IIFYM (If It Fits Your Macros)?
IIFYM means hitting protein, fat and carb targets with any foods that fit. What it says, what it does not, where fibre fits, and how a weekly budget helps.
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 Zyra Nutrition 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 Zyra Nutrition diet styles at 2,000 kcal: protein identical, fat 20–50% of the remainder or the keto ceiling. How to choose by adherence, with an 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 shifts.
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 includes food and all drinks. What counts, and why training changes it.
Reference valuesNutrition fundamentals8 minAre eggs bad for cholesterol?
In 17 trials in healthy people, extra eggs raised LDL cholesterol by about 8 mg/dL over 3 to 12 weeks. HDL barely moved. What that does and does not mean.
Human trial dataNutrition fundamentals9 minAre seed oils bad for you?
A recovered 1970s trial raised doubts, but a pooled study of 68,659 adults linked more linoleic acid, the main seed-oil fat, with fewer heart events.
Human trial dataNutrition fundamentals8 minCan you build muscle while intermittent fasting?
Yes, in trials so far. Lifters on a 16:8 eating window gained as much fat-free mass as normal eaters over 12 weeks, and less fat. What limits that finding.
Human trial dataNutrition fundamentals7 minDo smaller plates make you eat less?
Probably not by much. In a preregistered trial, 134 adults who served lunch on small or large plates ate only 19 kcal apart, and a 9-study review agreed.
Human trial dataNutrition fundamentals7 minDo ultra-processed foods make you eat more?
In trials, yes. On a research ward, 20 adults ate about 508 kcal a day more on an ultra-processed diet than on a matched unprocessed one. The likely reasons.
Human trial dataNutrition fundamentals8 minDo you really need 10,000 steps a day?
Not necessarily. In 47,471 adults, risk of death levelled off at about 6,000–8,000 steps a day in people 60 and over, and 8,000–10,000 in younger adults.
Human trial dataNutrition fundamentals9 minDo you need carbs to build muscle?
In 11 trials of lifters with protein matched, more carbohydrate made no significant difference to muscle growth (SMD 0.15). What the data does and does not say.
Human trial dataNutrition fundamentals8 minDoes alcohol ruin your sleep?
It changes sleep more than it ruins it. In 27 lab studies, alcohol cut REM sleep by about 11 minutes a night, even at low doses; total sleep was uncertain.
Human trial dataNutrition fundamentals8 minDoes eating slowly make you eat less?
Yes, in trials. Across 22 studies, slower eating led to less food at the meal, and a 2-week trial found 369 kcal a day less on slow-to-eat foods.
Human trial dataNutrition fundamentals7 minDoes exercise make you hungrier?
A little, for some. Across 51 trials, food eaten after a workout barely changed, and 18 of 24 training trials found no change in daily intake. Details here.
Human trial dataNutrition fundamentals7 minDoes eating more often change your metabolism?
No. With the same food, 2 vs 3 meals left daily energy use unchanged in a chamber study (8.2 vs 8.5 MJ, not significant), and digestion cost 9.4% vs 9.9%.
Human trial dataNutrition fundamentals7 minDoes your metabolism slow down with age?
A study of 6,421 people aged 8 days to 95 found daily energy use, adjusted for body size, stays flat from 20 to 60 and falls slowly after 60. What that means.
Human trial dataNutrition fundamentals8 minDoes muscle burn more calories than fat?
Yes, but less than claimed: at rest a kilo of muscle uses about 13 kcal a day and a kilo of fat about 4.5. Organs weighing a few kilos use far more than both.
Human trial dataNutrition fundamentals8 minDoes protein keep you full?
Mostly yes. In trials, higher-protein meals raised fullness ratings, and 19 adults on a 30% protein diet ate about 441 kcal a day less. The limits matter.
Human trial dataNutrition fundamentals7 minDoes sugar make you fat?
In 12 trials that swapped sugar for other carbs at the same calories, body weight did not change (0.04 kg). Sugar mattered through the calories it added.
Human trial dataNutrition fundamentals8 minHow many calories does walking burn?
Walking a mile at an ordinary pace cost about 80 to 90 kcal in two lab studies of young adults. Size matters most; speed matters less per mile than per minute.
Human trial dataNutrition fundamentals8 minHow much protein can your body use in one meal?
More than the 20–30 g rule suggests. In a 2023 study, 100 g of protein after training kept muscle building for 12 hours, with little extra burned for energy.
Human trial dataNutrition fundamentals7 minIs a high-protein diet bad for your kidneys?
In adults without kidney disease, 28 trials found no difference in the change in kidney filtering on about twice the protein. Kidney disease is a separate case.
Human trial dataNutrition fundamentals7 minIs fruit bad for you?
Across 11 trials of 3 to 24 weeks, eating more whole fresh fruit kept body weight steady or lowered it slightly; 7 of 11 pointed down. Juice differs.
Human trial dataNutrition fundamentals8 minIs the anabolic window real?
Not as a one-hour deadline. In a review of 23 trials, the protein-timing effect vanished once daily protein was matched; total protein predicted muscle gain.
Human trial dataNutrition fundamentals8 minLean bulk or “dirty bulk”: which builds more muscle?
In an 8-week trial of 17 trained lifters, a bigger calorie surplus mostly added fat: muscle thickness grew about the same at maintenance, small or big surplus.
Human trial dataNutrition fundamentals7 minPlant or animal protein for muscle?
With enough total protein and training, source mattered little: in a 10-week trial, vegan and meat-eating young adults both grew thigh muscle by 8.3%.
Human trial dataNutrition fundamentals7 minDoes more protein help women after menopause build muscle?
Not much beyond training itself. In a trial of women past menopause, 1.2 g/kg of protein a day added no extra muscle or strength over 0.8 g/kg in 10 weeks.
Human trial dataNutrition fundamentals7 minShould you eat before a workout?
For muscle over 12 weeks, fasted and fed lifters gained alike. Within a session, a meal helped: men did 68 squat reps after breakfast vs 58 without one.
Human trial dataNutrition fundamentals7 minShould you spread your protein throughout the day?
Mixed. One 24-hour study found about a third higher muscle building with even meals; longer trials matching daily protein mostly found no difference in lean mass.
Human trial dataNutrition fundamentals7 minWhat are the most filling foods?
In a test of 38 foods at 240 kcal each, boiled potatoes were rated about 3 times as filling as white bread. Heavy, watery, fibre-rich foods scored highest.
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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.