Privacy Policy — Lean

Effective date: April 2026

Summary

Lean is a body fat percentage coaching app for iPhone. Everything you enter — your stats, your body fat readings, your daily plans — stays on your device. We do not have servers. We do not collect, transmit, sell, or analyse your personal data, because we never receive it.

This policy exists to explain that in detail, to meet Apple's App Store requirements, and to set out your legal rights.

1. Who we are

This app is provided by LuminaryAI("we", "us", "our"). You can reach us at mattdray@luminaryai.co.uk

For the purposes of UK and EU data protection law, we are the data controller for the very limited personal data described below. In practice, because the app is local-only, we almost never come into possession of your data at all.

2. What Lean does

Lean is a single-purpose coach. It asks you for some information once (height, date of birth, sex, activity level, starting and goal body fat percentage, preferred reminder time), uses that information on your device to calculate a daily plan, and shows you your trend over time. Optionally, it reads body composition data from Apple Health.

3. What data Lean handles

All of the data below is stored only on your iPhone, in the app's local database. It is never transmitted to us, to our servers, or to any third party.

3.1 Information you provide directly

Date of birth
Sex (as relevant to metabolic calculations)
Height
Activity level
Starting body fat percentage
Goal body fat percentage
Body weight (optional)
Preferred reminder time
Preferred units (metric or imperial)
Your body fat readings when you log them manually

3.2 Information from Apple Health (optional)

If you grant permission, Lean reads the following data types from Apple Health:

Body fat percentage
Body mass (weight)
Step count (if enabled, used only to check whether you've hit a step-based daily habit)

Lean has read-only access. It never writes data back to Apple Health. It never requests write permission. You can revoke HealthKit access at any time in Settings → Privacy & Security → Health → Lean on your iPhone, and the app will continue to function with manual entry.

3.3 Information we do not collect

We want to be explicit about this:

We do not collect your name.
We do not collect your email address (unless you contact us for support).
We do not collect your location.
We do not collect your IP address.
We do not collect device identifiers for tracking purposes.
We do not use analytics (no Firebase, no Amplitude, no Mixpanel, no Google Analytics, no proprietary analytics).
We do not use advertising SDKs.
We do not use crash reporting services that transmit personal data.
We do not set cookies or any form of web tracker — Lean has no web content.
We do not use social media SDKs.

4. How we use your data

Because your data never leaves your device, we do not use it for anything. The app itself uses the data you enter to:

Compute your daily calorie target using the Mifflin-St Jeor equation adjusted for your activity level.
Compute your daily protein target from your estimated lean body mass.
Select the day's training focus from a 7-day rotation.
Draw your body fat percentage trend chart.
Schedule your local morning reminder notification.

That is the entirety of the processing. It happens on your iPhone, using your iPhone's CPU.

5. Apple Health and HealthKit

Apple imposes specific requirements on apps that use HealthKit. We commit to the following:

Health data obtained from HealthKit is used only for the health and fitness purpose of helping you track and reduce your body fat percentage.
Health data is never transmitted off your device.
Health data is never sold, licensed, or disclosed to third parties.
Health data is never used for advertising, marketing, or any similar service.
Health data is never shared with anyone, including us.
Health data is never used for research without explicit, separate, opt-in consent — and Lean does not currently conduct any research.

These commitments apply regardless of any other clause in this policy.

6. Notifications

Lean sends you one local notification per day at a time you choose, as a reminder to check your plan. This notification is scheduled and delivered entirely by your iPhone's operating system. It does not pass through our servers. We do not know whether you receive it, open it, or dismiss it.

You can disable notifications at any time in Settings → Notifications → Lean.

7. Third parties

Lean does not integrate with any third-party service, SDK, analytics provider, advertising network, cloud backup, or social platform. There are no third parties in this picture.

If this ever changes in a future version, we will update this policy, notify you in-app, and seek any required consent before the new integration starts.

8. Data storage and security

Your data is stored in a SwiftData database on your iPhone. It inherits the security properties of iOS:

It is protected by your device passcode, Face ID, or Touch ID.
It is encrypted at rest when your device is locked (per Apple's standard iOS data protection).
If you have enabled iCloud Backup and your device is backed up, a copy of the app's data may be included in that backup. iCloud Backups are encrypted in transit and at rest. Apple's privacy policy governs iCloud Backup — we have no access to it.
We do not operate any servers, so there is nothing for us to secure on our side.

9. Data retention

Lean retains your data on your device for as long as you have the app installed. To delete all data:

Delete individual readings from the Trend tab.
Reset your profile from Settings → Your stats → Reset (if implemented in the installed version).
Uninstall the app. Deleting the app from your iPhone deletes all of its local data, subject to any iCloud Backup you may have previously made.

We do not hold any copies, because we have never received the data.

10. Your rights

Under the UK GDPR and, where applicable, the EU GDPR, you have rights in respect of personal data we hold about you. These include the rights of access, rectification, erasure, restriction, portability, and objection.

Because we do not hold your personal data — it stays on your device — most of these rights are exercised directly through the app itself: you can view, edit, and delete your data at any time. If you believe we do hold personal data about you (for example, if you have contacted us by email for support), you can exercise your rights by writing to [CONTACT EMAIL], and we will respond within one month.

You also have the right to lodge a complaint with a supervisory authority. In the UK, that is the Information Commissioner's Office (ico.org.uk).

If you are in California

Under the California Consumer Privacy Act (CCPA), you have the right to know what personal information is collected, to delete it, and to opt out of its sale. We do not sell personal information and we do not collect personal information from you remotely. Rights of access and deletion are exercised, as above, directly within the app.

11. Children

Lean is not directed at children under 13 (or under 16 in parts of the EU). The app discusses calorie targets and body composition, which are not appropriate subject matter for children. We do not knowingly process data from children. If you are a parent or guardian and believe your child has used the app, uninstall it from their device — doing so removes all data.

12. International users

Because no data leaves your device, there is no international transfer of personal data for us to disclose. The app works the same way everywhere.

13. Lean is not medical advice

This is not strictly a privacy matter, but it bears repeating here: Lean provides general fitness coaching based on standard exercise science. It is not a medical device, not a diagnostic tool, and not a substitute for advice from a qualified healthcare professional. If you have a health condition, are pregnant, have a history of eating disorders, or are taking medication that affects metabolism, please speak to your doctor before acting on Lean's recommendations.

14. Changes to this policy

If we update this policy, we will:

Change the "Last updated" date at the top.
Show a notice in the app the next time you open it after the change.
Where the change materially affects your rights, ask for your acknowledgement before continuing.

We will not retroactively reduce the protections described in this policy.

15. Contact

If you have any questions about this policy, your data, or how Lean works, please write to:

mattdray@luminaryai.co.uk

We aim to reply within five working days.

This policy is published in English. If it is translated into other languages, the English version prevails in the event of any conflict.