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Who’s behind Evzia

I’m Alberto López Pérez, and I make Evzia, a personal project from Spain. This page tells you who I am, where the app comes from, how its numbers are worked out and how this website is written.

Service owner

These are the owner’s details for Evzia. The tax ID (NIF) and address required by article 10 of Spain’s Law 34/2002 on information society services and electronic commerce (LSSI-CE) are on Support and in the terms of use.

Owner
Alberto López Pérez
Email
colkard96@gmail.com

Plan prices, with VAT included, are on Pricing. How the service is provided is in the terms of use, and how your data is handled, in the privacy policy.

Why Evzia exists

Evzia started at home. I wanted my parents to log what they eat and their weight without fighting with an app, and I wanted both of them to see the same thing on their phones.

They’re not tech people, so every screen had to make sense at first glance: big buttons, clear text and few screens. That led to some things everyone who uses the app has today:

  • Large text, so you can read without glasses. It’s a setting on your phone, not a separate app.
  • Batches, because at home big dishes are cooked for several people, and each person needs to know how much to serve themselves.
  • “Undo” instead of asking “are you sure?” at every step.
  • Getting in without passwords and without creating an account.

Later more people joined and more things were added, until it stopped being a home app: today you can use it on your own or in a group. I keep building it with the same idea: logging should be easy, the numbers should be visible, and the app should say when it’s estimating.

How the numbers are worked out

Evzia’s numbers use published formulas, show where each number comes from and say when something is an estimate. This is what the app does.

Your starting point comes from formulas, not from AI

daily burn = resting × 1.2 + what you walk + exercise

Resting energy is calculated with the Mifflin-St Jeor equation (weight, height, age and sex). The × 1.2 covers the rest of the day, not counting walking. Walking is calculated from your steps: your stride is 0.414 times your height and each kilometer burns 0.5 kcal per kilo, according to the ACSM. The treadmill uses the ACSM equations for walking and running, and the other activities use the METs from the 2024 Adult Compendium of Physical Activities. Everything is net: without resting energy, which is already in the first term.

It’s an estimate and it says so: the resting equation can be off by around 10% and the × 1.2 is an assumption.

Then, from your data

maintenance = what you eat on average − (weight change × kcal per kilo ÷ days)

Until there’s data, the formula rules. After about two weeks of logging what you eat and weighing yourself often (at least 8 weigh-ins spanning 14 days and 7 well-logged days, meaning days that weren’t left half done), Evzia starts looking at the last 28 days: what you ate on average and how your weight changed, based on its trend and not on a single weigh-in. What you weighed before you started logging doesn’t count. It blends the result with the formula according to how reliable each piece of data is: the better logged and weighed the days are, the more the scale counts. If you change phase, for example from a deficit to a surplus, it notices from what you eat and adjusts the estimate from that day on. It never changes your kcal goal on its own: it’s information.

How much a kilo is worth

Not everything that goes up or down on the scale is fat, and a kilo of fat has many more kcal than a kilo of fat-free mass. Evzia estimates your body fat percentage with the Deurenberg formula (BMI, age and sex), splits the weight change between fat and fat-free mass with the Forbes relationship (which Hall revisited) and works out the kcal of each part. That way it gives each person their own kcal per kilo, instead of one number for everyone.

Protein

The protein goal is calculated per kilo of body weight (the setup guide suggests between 1.2 and 1.8 g per kilo a day, depending on your goal, and you can adjust it) and is recalculated with your latest weight.

The AI suggests, you confirm

The AI calculates what isn’t already in your foods. Nothing adds to your day until you confirm it, anything optional stays out of the total, and anything that’s an estimate is marked “(est.)”. When a food has real values, from a label or ones you corrected yourself, they take priority over generic ones. Energy use, maintenance and the setup guide’s recommendations are formulas, not AI.

What Evzia is not

Evzia is not a medical device and does not replace a doctor, dietitian or trainer. Its numbers are estimates: check them before logging them. If you have an illness, are pregnant, take medication or are about to change your eating or exercise a lot, talk to a professional first.

Sources

How this website is written

I write the text on this website, with the help of an artificial intelligence, and I review it before publishing. Last reviewed: . If you see anything that doesn’t match what the app does, write to me.

The calculators in Tools use the same code as the app: if a calculation changes in the app, it changes on the website. They run in your browser, without sending or saving anything you type, and their examples use made-up people.

This website has no advertising and no third-party analytics.

Contact

Write to me at colkard96@gmail.com with any question, error or request, and I’ll reply as soon as I can. For help with the app, see also support, and to delete a group’s data, how to do it.