Sigma is made by one person. Mail gets read, and an answer usually takes a day or two.
support@sigmanutrition.app
Most questions are answered faster by the guide, which is the same one that ships inside the app.
Sigma has no sign-up, no password and no server. Nobody can lock you out of it and there is no account for anyone to recover. If the app is on your phone, your food log is on your phone.
On the device, in Sigma's own storage. If iCloud is on, a private copy syncs through your own iCloud account, the same way Notes or Health do. That copy is yours: it counts against your storage, and the developer cannot see it, because there is no server on the other end to see it with.
Settings, then Data, then Export CSV. It writes every entry with its date, food, amount and macros, and it reads back in through Import. That round trip is tested on every build, because a log you cannot take somewhere else is not really yours.
Settings, then Data, then Wipe all data. It asks once and says plainly that it cannot be undone. Deleting the app removes the local copy; if iCloud sync is on, delete the data first or it comes back when you reinstall.
Sigma searches USDA FoodData Central and Open Food Facts, which are public databases rather than a catalog anyone curates for you. Homemade and local food is in neither, and that is expected. Add it once with Custom food and it lands in Your foods, where a tap logs it from then on.
Typed searches are the one thing that leaves the phone, and only the words you type go, straight to those two databases. Nothing comes back to the developer.
Both run on Apple Intelligence, on the device. They need an iPhone that supports it, with Apple Intelligence turned on in Settings, and the model downloaded. The app says which of those is missing rather than failing quietly. Everything else in Sigma works without it.
They are, on purpose. A day rounds to the nearest 100 calories and wears a tilde, because the inputs are estimates and showing 1,847 would claim a precision that portion sizes and database averages do not have. The stored numbers are exact; only the display rounds.
Mail support@sigmanutrition.app. Useful things to include: what you did, what happened, what you expected, and the build number from Settings. A screenshot helps. Do not send your CSV unless asked, and never send it if it holds anything you would not want in an inbox.
It does not set targets, predict your weight, score your day or tell you what to eat. That is a design decision rather than a missing feature, and the guide explains why.