Precision Physiques

Coaching

The complete platform for a one-person online coaching business — AI drafts each client's nutrition plan, the coach approves every one before it ships.

Precision Physiques coach console — the cohort roster, review queue and each client's targets (demonstration data)
The challenge

A one-person coaching business writes every client's nutrition plan by hand — a bottleneck on how many clients one coach can properly serve.

Those plans carry special-category health data under UK GDPR, so the system holding them had to be built to that standard from day one, not bolted on after the fact.

The obvious build — hand a model the client's details and print what comes back — is the one that fails here. A plan is arithmetic before it is food, and a language model that is a little wrong about a calorie target is wrong for a real person for a whole week. When the coach was given freedom to set his own goal adjustments, a measured spread of realistic client profiles put nearly half of the resulting targets below the client's own resting burn.

What was built, and why it was built that way

A marketing site, a client-accounts app, and the coach console that runs both. A deterministic engine (Mifflin-St Jeor) sets each client's calorie and macro targets; AI drafts the meal plan around those targets, honouring allergies and preferences.

The split is the whole design: the engine owns the numbers and the model owns the food. Nothing a model returns is allowed to become a calorie target, and the targets it writes around are floored twice over — never below a client's own resting burn, never below a hard minimum set by sex, and never generated at all below the very-low-calorie line the platform refuses to aim at. The floor is never silent either: when it bites, the coach sees that it bit and by how much, rather than a number that quietly moved.

One rejected approach is worth naming. Allergies were first handled by matching words in food names against what the client had typed, and that filter was hardened five times and beaten five times — mostly in the wrong direction. Across a measured run of forty-eight plans for eight realistic clients, twelve of the fourteen failures were the filter refusing food the client could perfectly well eat: peanut butter withheld from someone avoiding dairy, olive oil from someone who disliked olives, oats treated as gluten. Removing it took that run from 71% to 96%. What replaced it is a vetted list decided once per client, which the plan writer is then bounded by — a food that is not on a client's list cannot appear on their plate whatever its name contains. The coach sees every list with its reasons and can exclude anything he disagrees with, and the platform will not let him allow a food whose own packet declares, at high confidence, an allergen that client named.

The console is where the coach actually works — the cohort roster, six plan slots per client, a plan wizard that regenerates a plan at a new calorie target, an editable food library, client messaging, progress photos and a weigh-in that reflows every plan a client holds.

Plan generation fails towards refusal, deliberately. A drafted week that lands too far from its target is not quietly stored as a plan — it is held, flagged, and cannot be released to a client. The direction of that error was chosen rather than inherited: refusing costs the coach a regenerate, while accepting costs a client a bad week.

Nothing reaches a client until the coach has reviewed and approved it. The backend runs on an isolated Firebase project with consent capture, an audit log and data export built in — because the data involved is health data, not an order history.

Isolation is enforced rather than intended: this platform runs on its own backend project, shared with nothing else MAST has built. A subject-access request is answered by one call that gathers everything held about a client — plans, messages, photos, requests and the coach's own private notes, including drafts that were generated and never released to them — and every export writes a durable record of who ran it and when.

Screenshot walk-through

What it actually looks like, running.

Precision Physiques coach console — the plan wizard, an AI-drafted week of meals and its approval state (demonstration data)
The coach console, drafting a plan — targets on the left, the AI-drafted week on the right, and an Approved badge that says it has been released. Shown with demonstration data; no client record appears anywhere on this page.
Precision Physiques client app on mobile — an approved plan released by the coach (demonstration data)
What the client gets: their approved plan, a PDF to take to the shop, messages to the coach and progress tracking — marked released by your coach, because the coach released it.
Precision Physiques — live online coaching platform
The marketing site in front of it all — built and deployed, ready to onboard clients.
What it meant

A one-person coaching brand gets the plan-writing capacity of a much bigger operation, with every plan checked and approved by the coach before a client ever sees it — built and deployed, ready to onboard, on a data-protection design set up from the start rather than fixed after the fact.

Getting there took a testing habit most builds skip. The free test lane runs on stubs and emulators and can be run all day, and it is blind to the things that actually break a live site — served copy, real timing, real data. So a second gate runs the real thing, real model calls and all, before anything ships, because a green emulator suite once hid four separate faults on the deployed site.

The engineering that matters here is not the drafting. It is that a coach's judgement sits on top of it, the arithmetic underneath it is not the model's to get wrong, and the client's data was treated as special-category from the first commit rather than the first complaint.

The stack
Isolated Firebase projectCloud FunctionsGemini (meal drafting)Deterministic macro engineClinical floor gatesPer-client vetted food listCoach consoleFirestore + consent capture

Half an hour to see what a compliance-grade client platform looks like for your business.

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matt@mastconsult.co.uk · MAST Consulting is a sole trader.