I am currently deciding whether to use the USDA's Nutritional Database as the backend provider of nutritional information for my app. The other option I am considering is the FatSecret platform. My concern about the USDA API is there are no guarantees as it's not a business. Has anyone built real-time analytics/apps with the USDA API and can you tell me whether you've had good performance? Have there ever been gaps in service/etc?
In general, government APIs and databases have no SLAs (Service Level Agreements) associated with them. If performance is an issue, you may need to consider an alternate provider.
For cases where the data is freely available as dumps (and not just limited to queries), it's often straight forward to ingest the data into your system as is. If there's enough demand for the service with an SLA, it's possible that some commercial company might provide this (at some cost).
As for gaps in service ... against, without an SLA, it's difficult to say what qualifies as a 'gap'. I'm going to say that they're all going to be unreliable if we run into another government shutdown ... as for the last one, we were required to take all websites offline without being granted an exemption (such as them being required to protect property or human life).