If you use Android, use the email of your Google account: it's the only one Play accepts.
You can pick more than one. Don't write any health data about yourself or others here.
Privacy notice. Controller: Nicola Rigato, privacy@mangiamy.com. I use your data only to select testers for the Mangiamy beta and send you the invitation; legal basis: your consent, which you can withdraw at any time by writing to privacy@mangiamy.com. If you are selected, your email is added to the tester list of Google Play or Apple TestFlight, which process it under their own terms. This form is hosted by Tally (Tally BV, Belgium). I delete the answers of people who are not selected within 30 days of the end of the beta, and those of testers within 90 days of the end of the beta. You can request access to, correction or deletion of your data, and lodge a complaint with your data protection authority.