In addition to general security measures like locking your smartphone, you can protect mediteo with an additional authentication. 

More → Settings → Use authentication on/off

If activated, mediteo will ask for your Touch ID/Face ID/PIN every time you open it.

You can also use backups to protect your data from loss. Find out more information about this on How can I create a backup in my account/restore a backup from my account? – mediteo.